Companion Biology XII - S. Dinesh & Co.

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��Each and every organism lives for only a certain period after which it meets a natural death. The

period between birth and natural death of an organism is called life span. Life span varies from lessthan one day to more than 4000 years. Life spans are not related to size or complexity of the organisms.Crows and parrots are of equal size. Crow has a life span of only 15 years, while parrot lives for about140 years. Similarly, Mango tree lives for about 200 years while Peepal (Ficus religiosa) has a life spanof about 2500 years. Banyan tree (Ficus bengalensis) spreads over a very large area but does not live beyond500 years. The largest living plant is a shrub called Lomantia tasmanica. It is 43,000 years old. The longestlife span amongst animals is that of an edible clam Arctica islandica. It is 410 years. Therefore, life spanis a specific trait of each organism. It depends upon the timing of natural death. Natural death is acertainity in every individual organism. No organism is immortal. However, some single-celled organismsdo not have a natural death. When they grow up, they undergo binary fission. A mother cell divides into twoequal daughter cells. No body part is left to die. Such organisms are immortal.

Reproduction is a characteristic feature of all organisms. It is the biological process of self perpetuationor continuation of species in which the grown up individuals give rise to young ones similar to them. Theadults who give rise to young ones are called parents. The young ones are called daughters or offspring (bothsingular and plural). The young ones grow, mature and repeat the process. There is thus a cycle of birth,growth, maturity and death. Reproduction ensures the continuity of species generation after generations.

�� 1. Continuity of Species. A species continues to live indefinitely because of the reproduction of its

individuals.2. Replacement. It replaces individuals dying due to senescence or ageing, predation and disease.3. Population Organisation. It maintains population organisation consisting of young, adults and aged

individuals.4. Life. Life can exist on earth only if there is reproduction of living organisms.5. Variations. Reproduction introduces variations in structure, function and behaviour. They produce

individuality of living beings.6. Useful Variations. Useful variations persist in the individuals. They are transferred to new

generations. Useful variations help in adaptations and evolution.

�� Reproduction is characterised by a number of basic features.1. Replication or formation of carbon copies of DNA.2. Formation of RNAs, proteins and other biochemicals for multiplication of cellular contents.3. Growth of cells.4. Division of cells. It is mode of reproduction in many unicellular organisms.5. Formation and separation of reproductive units.6. Development of new individuals from reproductive units.

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� Fig. 1.1. Approximate life span of some organisms.

�� Though basic principles of reproduction are similar in all organisms, the mechanism to multiply and

produce offspring shows large diversity. It is due to differences in their organisation, structure, physiology

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�� and habitat. Broadly speaking, there are two types of reproduction, asexual and sexual. Asexual reproductiondoes not involve gamete formation and gamete fusion. It is uniparental. Sexual reproduction consists offormation of gametes and fusion of gametes of opposite sexes. It is biparental with two types of parents ofdifferent sexes.

Differences Between Asexual and Sexual Reproduction

S. No. Asexual Reproduction Sexual Reproduction

1. It is uniparental. It is generally biparental but can be uniparental.

2. Asexual reproduction is somatogenic. It is germinal.

3. Sex organs do not participate. Sex organs participate during this type of reproduction.

4. Meiosis does not occur. Meiosis occurs once during life cycle.

5. Formation of new individual does not There is formation and fusion of gametes.involve fusion of gametes.

6. A new individual develops from specia- A new individual or offspring develops from fusionlised or unspecialised somatic part of the product of gametes, called zygote.parent.

7. The daughters are genetically similar The offspring have an admixture of the genetic make-upto the parent. of the two parents.

8. It does not introduce variability. It introduces variability.

9. It is a quick method of multiplication. It is a comparatively slower method of reproduction.

10. Adaptability and evolutionary signifi- It is important both for adaptability and evolution.cance are absent.

�� !�"�#��!$��%"�&��'It is a mode of multiplication in which new individuals develop from a single parent with or without

gamete formation which does not involve fusion of sex cells. Meiosis has no role in asexual reproduction.All divisions are generally mitotic. All the individuals formed through asexual reproduction from aparent are morphologically and genetically similar to one another as well as their parent. They are cloneof their parent as well as of one another. The term ramets is used for members of a clone.

Asexual reproduction is common among lowly organised living beings, viz, unicellular organisms,simple plants and simple animals. It is absent in higher invertebrates and vertebrates. Many higher plantsshow a type of asexual reproduction called vegetative reproduction.

Characteristics of Asexual Reproduction

(i) It is uniparental. i.e., the individual receives the whole set of chromosomes from one parent only.

(ii) Unit of reproduction or propagule is an unspecialised or specialised part of parent.

(iii) The propagule is commonly formed from somatic cells of the parent. Therefore, asexualreproduction is also called somatogenic reproduction.

(iv) There is no fusion of gametes. Because of it asexual reproduction is also known as agamogamyor agamogenesis.

(v) Meiosis is generally absent. All divisions are mitotic.(vi) The young individuals derived from the same parent are genetically similar to one another as

well as to the parent.(vii) Haploid-diploid alternation does not occur.(viii) It is a quick method of multiplication.(ix) A very large number of individuals can be produced by a parent.(x) The progeny produced through asexual reproduction is of uniform size, shape and other characteristics.

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�� Asexual reproduction occurs by fission, torulation, sporulation, fragmentation, regeneration,

parthenogenesis and vegetative reproduction.

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It is a mode of asexual reproduction in which body of a mature individual divides into two or moresimilar and equal sized daughters. In unicellular organisms, protists and monerans, cell division resultsin fission. Therefore, it is the mode of asexual reproduction in them. Fission can occur by binaryfission, multiple fission and plasmotomy.

1. Binary Fission (Fig. 1.2). It is the division of the body of an individual into two equal halves, each ofwhich functions as an independent daughter individual. In unicellular organisms, binary fission is accompaniedby mitotic division of nucleus followed by cytokinesis. In metazoans the multicellular individual divides intotwo daughters by a sort of constriction or cleavage. The organisms showing binary fission seldom die ofsenescence or old age because as soon as they mature, they divide into two daughters. They are, therefore,nearly immortal. Depending upon the plane of division, binary fission is of the following types :

(i) Simple Binary Fission (Irregular Binary Fission). Division can occur through any plane, e.g.,Amoeba.

(ii) Longitudinal Binary Fission. The plane of fission passes along the longitudinal axis of theanimal, e.g., Euglena, Vorticella.

(iii) Oblique Binary Fission. The plane of binary fission lies at an angle to the transverse axis, e.g.,Ceratium, Gonyaulax.

(iv) Transverse Binary Fission. The plane of binary fission runs along the transverse axis of theindividual, e.g., Paramoecium, diatoms, bacteria. In Paramoecium transverse binary fission is precededby amitotic division of meganucleus and mitotic division of micronucleus. Binary fission produces twodissimilar daughters, one proter (anterior) and the other opisthe (posterior). Both develop the deficientcomponents and become similar.

Planaria (Dugesia) also resorts to binary fission occasionally. It fixes its posterior part firmlyamongst stones and pulls the anterior part. The middle part constricts and breaks to form two individuals.Each new individual develops the missing parts.

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� Fig. 1.2. Binary fission in some animals.

�� *2. Multiple Fission. A number of daughters are

produced from a single parent. The nucleus of the parentdivides repeatedly to form a number of daughter nuclei.Cytoplasm cleaves in such a way that a small amount ofcytoplasm gathers around each nucleus. This divides theparent cell into a number of tiny but similar daughtercells, e.g., Plasmodium, Amoeba, Monocystis. InPlasmodium, multiple fission occurs during schizogony as

well as sporogony. In Monocystis, multiple fission occurs during gamete formation by each of the twogamonts present inside a gamontocyst. The resultant gametes fuse in pairs to produce zygotes. Thezygotes secrete an envelope and get changed into zygocysts, popularly called spores. Each zygocystproduces eight sporozoites.

Multiple fission of some Amoeba species occurs during unfavourable conditions. Amoeba withdraws itspseudopodia and secretes a 3-layered hard covering or cyst. The phenomenon is called encystation.Encystation is meant for perennation. On the approach of favourable conditions, multiple fission occurs inthe encysted Amoeba. It produces a number of minute amoebae (=amoebules) or pseudopodiospores. Cystwall bursts to release amoebae or pseudopodiospores in the surrounding medium. They grow to form matureamoebae. Sometimes, instead of forming a single cyst, Amoeba produces a number of encysted spores orensheathed amoebae. The phenomenon is called sporulation. Encysted spores take part in both dispersal andperennation. Under favourable conditions each spore gives rise to a small Amoeba.

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�Fig. 1.4. Sporulation and Encystment in Amoeba A—B, cyst and pseudopodiospores. C—E, sporulation.

3. Plasmotomy. It is modification of multiple fission. Plasmotomy occurs in multinucleate or syncytial

organisms. During reproductive phase, the cytoplasm cleaves with or without simultaneous divisions of

nuclei. As a result, a number of daughters are formed each with one to a few nuclei, e.g., Opalina,

Pelomyxa (=Chaos, Giant Amoeba).

�Fig. 1.3. Multiple fission in Plasmodium.

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Differences Between Binary Fission and Multiple Fission

S.No. Binary Fission Multiple Fission

1. It produces two daughters. It forms a number of daughters.

2. Nucleus divides only once. Nucleus divides repeatedly.3. Cytoplasm cleaves to produce two daughters. Cytoplasm collects around each nucleus to form

several daughters.4. No residue is left in binary fission. A residue is left behind.5. It makes the organism immortal. Immortality is absent.6. Binary fission takes place under favourable Multiple fission can occur under favourable

conditions. conditions in some (e.g., Plasmodium) as well asunfavourable conditions (e.g., Amoeba).

Examples. Amoeba, Paramoecium, bacteria, Examples. Plasmodium, Monocystis, Amoeba.diatoms.

�� Torulation is budding in unicellular organisms, e.g., Yeast, oidia of Rhizopus and other fungi. The

unicellular structure develops an outgrowth on one side. Nucleus divides. One daughter nucleus shifts into theprotuberance. The protuberance or bud grows, constricts at the base and separates. Sometimes a cell may beartwo or more buds, each of which grows more buds. The complex budded condition is called torula stage.

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�Fig 1.5. Torulation or budding in Yeast.

Differences Between Binary Fission and Budding in Unicellular Organisms

S.No. Binary Fission

1. Division is equal.

2. A protuberance is not formed.

3. Nucleus divides first followed by divisionof the cytoplasm.

4. Parent cell disappears.

Budding or Torulation

Division is unequal.

A protuberance or bud is formed.

Cytoplasm gives out an outgrowth prior todivision of nucleus.

Parent cell remains intact.

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�� Spores are minute single-celled thin-walled propagules which have dual function of dispersal and

formation of new individuals. Sporulation or spore formation is common in members of monera,protista, fungi and algae. Motile spores are called zoospores. They occur in aquatic organisms, e.g.,Chlamydomonas, Ulothrix. The nonmotile spores are named variously, e.g. aplanospores, hypnospores,akinetes, conidia, etc. Some spores are produced exogenously (e.g., conidia in Penicillium) while othersare formed inside sporangia (e.g., sporangiospores in Rhizopus).

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�Fig 1.6. Sporulation. A, Zoospores of Chlamydomonas. B, Conidia of Penicillium.

�� (L. fragmere—to break)

It is breaking of the body of theparent into two or more pieces, each ofwhich becomes an as independentindividual. Fragmentation occurs bynatural death and decay of older partsreaching the area of branching inMarchantia, Riccia and other bryophytes.It takes place by mechanical injury or emptying of intervening cells in Spirogyra and other algae. It alsooccurs in fungi, Hydra, sponges, some annelids and echinoderms (sea stars). Each fragment undergoes mitosisand grows into adult capable of producing offspring.

� � � ��(L. re—again, generere—to beget)

It is a type of asexual reproduction as well as method of repair of injured or missing parts, e.g., Hydra, Planaria(Dugesia), sponges, echinoderms. Regeneration is the process of renewal, restoration and growth which can occurat the level of cells, tissues and organs. If the organism has lost a part or is cut into two or more pieces, reservecells of the body proliferate and form the missing parts. Regeneration of the whole body from a fragment,however, a method of reproduction in only lowly organised individuals (morphallaxis). In higher forms, it is used forlimited repair (epimorphosis) either of certain damaged tissues (reparative regeneration) or development of

severed body part (restorative regeneration), e.g., broken tail in Lizard, partially damaged liver in humans.

��-� �� It is a mode of asexual reproduction in which a new individual develops from a specialised internal or

external part or bud of the individual having one or more totipotent cells. Budding is of two types,exogenous and endogenous.

�Fig 1.7. Fragmentation in Spirogyra.

�. �� 1. Exogenous or External Budding. An outgrowth of proliferating cells or bud develops from the body

surface of the parent individual. The bud grows in size and forms a young individual. The bud and the youngindividual grow at the expense of nutrients provided by the parent. Soon the growing young individualbecomes nutritionally independent. It may separate from the parent to lead a free life (e.g., Hydra, Fig. 1.8)or remain attached to the parent to form a colony, e.g., Scypha (=Sycon, Fig. 1.9).

�Fig. 1.8. External budding in Hydra.

A colony may have two or more than two individuals called zooids, e.g., Obelia.

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�Fig. 1.9. Budding and colony formation in Scypha (=Sycon).

2. Endogeneous or Internal Budding.Specialised structures capable of forming newindividuals develop inside the body of the parent.They are internal buds. Internal buds of spongesare called gemmules, e.g., Spongilla (fresh watersponge). A gemmule consists of a mass of totipotentcells called archaeocytes. It is surrounded by anopaque envelope with or without spicules. Amicropyle is present on one side for the liberationof archaeocyte mass during germination ofgemmule. Gemmules take part both in perennationand dispersal. Similar internal buds calledstatoblasts occur in bryozoans.

3. Strobilation (Strobilization). It ismultiplication by body segmentation as formation ofproglottids in Taenia or ephyra larvae in Aurelia.

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�Fig. 1.10. Structure of a gemmule.

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�� (i) It is uniparental. Thus there is no need to search for a mate.

(ii) It is a rapid mode of reproduction.(iii) It helps in quicker establishment of young ones.(iv) The young ones are exact replicas of their parent.(v) Asexual reproduction is simpler than sexual reproduction.(vi) Consumption of resources is lower.

�� (i) As there is rapid multiplication, a large number of young ones are formed. It causes overcrowding.

(ii) There is no mixing of genetic material. So no new combination or variation takes place.(iii) There is no crossing over. New linkages are not formed.(iv) It has no role in evolution.(v) Adaptability to changes in environment is low due to absence of new variations.

��Vegetative propagation is the formation of new plants from somatic parts like roots, stem, leaf or

bud. It is a method of asexual reproduction as it is uniparental in nature and does not involve formationof sex cells. Vegetative propagation occurs naturally in many plants. A number of techniques have beendeveloped by farmers and gardeners to propagate useful plants vegetatively for both quicker multiplicationand uniform progeny.

�� They are methods of plant multiplication occurring naturally in which a somatic part of the plant detaches

from the body of the mother and develops into a new independent plant under suitable environmental

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�Fig. 1.11. Natural propagation. A, eyes of Potato, B, rhizome pieces of Ginger. C, bulbil of Agave. D, leaf

buds of Bryophyllum. E, offset of Water Hyacinth.

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conditions. The detachable somatic part that functions in vegetative propagation is called vegetativepropagule. It carries one or more buds. Natural buds occur over the nodes of the stem. When placed incontact with damp soil, the buds sprout, producing roots and new plants. The potential is exploited byfarmers, e.g., tubers of Potato, rhizome of Banana and Ginger, suckers, bulbs, runners, offsets, stolons,aerial stems, etc. Some propagules carry adventitious buds, e.g., normal and storage roots, leaves. Bulbilsand turions are buds which take part in natural propagation.

� Parthenospore. A spore is formed directly from a gamete. It is also called azygospore.

� Parthenogamy. It is the union of two incompatible gametes like two female gametes.

� Parthenoapogamy. It is the fusion of vegetative nuclei.

� Parthenocarpy (Noll, 1902). It is the formation of fruits without fertilization. It is uselessin case of plants where seeds provide the economic produce, e.g., Almond, Walnut,Coconut, Pomegranate.

� Pseudogamy. Embryo develops without fertilization but pollination is required.

� Monoecy. Monoecious condition.

� Dioecy. Dioecious condition.

1. Roots. Roots of some plants develop adventitious buds and take part in vegetative propagation.Tap roots taking part in vegetative reproduction are found in Dalbergia (Sheesham), Albizzia, Guava,Populus (Poplar), Murraya, etc. Fleshy adventitious roots which help in vegetative propagation are metwith in Sweet Potato, Dahlia, Asparagus and Tapioca.

2. Underground Stems. All types of underground stem structures can take part in vegetativepropagation.

(i) Stem Tubers. They possess buds over their nodes or eyes. The buds sprout to produce newplantlets when a stem tuber or a part of it having an eye is placed in the soil e.g., Artichoke, Potato.

(ii) Bulbs. They are underground condensed shoots having fleshy scales and internal buds. Whensown in soil, buds present inside the bulbs sprout to from new plants, e.g., Garlic, Narcissus, Onion.

(iii) Corms. They are vertically oriented unbranched swollen underground stems with circularnodes having scale leaves and buds. The buds give rise to new plants, e.g., Freesia, Colocasia, Crocus,Amorphophallus (Zamikand).

(iv) Rhizomes. They are perennial underground fleshy main stems which possess buds for growthof new aerial shoots during favourable season and storage of food for perennation during unfavourableseason. Parts of rhizome separated by natural decay and other reasons give rise to new plants, e.g.,Ginger, Turmeric, Banana, Dryopteris, Adiantum.

(v) Suckers. They are stem branches which develop from underground base of an aerial shoot andgrow out to form new aerial shoots. When the suckers break due to decay or mechanical injury, anumber of daughter plants are formed from one, e.g., Chrysanthemurn, Mint.

3. Subaerial or Creeping Stems. There are three types of subaerial or creeping stems which takepart in vegetative propagation —runners, stolons, offsets.

(i) Runners. They are special, narrow, green, horizontal creeping branches which grow from thebase of an aerial shoot, strike roots at intervals and form new aerial shoots. Breaking of runners formnew plants, e.g.,Cynodon (Lawn Grass), Oxalis, Centella.

(ii) Stolons. They are special arched subaerial prostrate branches which grow from the base of anaerial shoot. They develop new aerial shoots from their tips. Stolons help in formation of new plants,e.g., Wild Strawberry, Jasmine.

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(iii) Offsets. They are one internode long prostrate brnaches found in some aquatic plants like Pistia(Water Lettuce) and Eichhornia. Breaking of offsets help in vegetative reproduction.

Terror of Bengal. It is the title given to aquatic plant, Water Hyacinth (Eichhornia crassipes).The plant was introduced in water bodies of Bengal for its beautiful flowers and shape of leaves.However, it turned out to be highly invasive water weed and scourge of water bodies that notonly spread to all standing water bodies of Bengal but also throughout India due to its rapidvegetative multiplication through offsets. It is very difficult to get rid off. The plant drains outoxygen from water. It results in asphyxiation and hence death of the fishes and other animals. Byits dense growth, Water Hyacinth also kills other plants.

4. Aerial Shoots. Buds present on certainstems can directly give rise to new plants whenstem segments fall on the soil, e.g., phyllocladesof Opuntia. Sugarcane is multiplied vegetativelyby planting segments of basal part of stemhaving at least one node.

5. Leaves. Leaves of some plants developadventitious buds for vegetative propagation.In Bryophyllum, such buds develop in themarginal notches of the leaves. The buds growinto plantlets in the intact leaves of Bryophyllumdiagremontium. In other species the buds sproutonly when the leaf falls on the soil. In Begonia,only the injured parts of leaves develop buds.In walking fern, Adiantum caudatum, the leaftips develop buds and form new plants whenthey happen to come in contact with soil. Leavesof Kalanchoe, Streptocarpus and Saintpauliaalso take part in vegetative propagation.

�� !�� Artificial methods are man-made special techniques in which part of somatic body of a plant is made to

develop into new independent plant. Artificial methods are used to propagate desired varieties according tohuman requirements. Rainy and spring seasons are the best periods for vegetative propagation. The varioushorticultural methods of vegetative propagation are as follows :

1. Use of Special Vegetative Organs. They are used in vegetative propagation through techniqueswhich are refined forms of the ones found in nature.

(i) Rhizomes. Rhizomes are cut into smaller pieces, each having a few to many buds. On placing inthe moist soil, each rhizome piece gives rise to one or more plants.

(ii) Tubers. Artichoke and Potato tubers are cut into smaller pieces, each having one or more eyes.They are used as seeds for development of new plants.

(iii) Corms. Both corms and cormels (larger buds) are used for vegetative propagation, e.g.,Colocasia, Crocus, Gladiolus.

(iv) Bulbs and Bulblets. Onion is not propagated vegetatively by bulbs but can be done so with the helpof bulbils formed amongst the flowers. Bulblets are used in case of Garlic and some lilies. Bulb is cut intopieces for vegetative propagation in Narcissus.

(v) Suckers. They are helpful in propagation of Mint and Chrysanthemum.

�Fig. 1.12. Propagation from stem cutting

in Sugarcane.

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�� (vi) Stolons. A number of young plants are formed in nurseries from a single plant of Strawberry by

means of stolons.

(vii) Fleshy Roots. Sweet Potato and Dahlia have fleshy roots, each of which can give rise to one ormore daughter plants.

(viii) Bulbils. Fleshy buds or bulbils develop in a number of plants. They are plucked and planted. Eachbulbil gives rise to a new plant, e.g., Pineapple, Cycas, Agave.

2. Cuttings. Cuttings are segment of root, stem and leaves which are planted in their natural polarisedposition. Rooting is hastened by root promoting chemicals e.g., NAA, IBA. The best season for cutting isearly spring or rainy season.

(i) Leaf Cuttings. Sansevieria (Snake Plant) is multiplied vegetatively by leaf cuttings. A leaf is cuttransversely into two or more pieces. The leaf cuttings are planted vertically in their natural polarity. Rootpromoting hormone may be used for quickening development of adventitious roots.

(ii) Root Cuttings. In some plants root cuttings of 20—30 cm length are used for propagation of plants,e.g., Blackberry, Raspberry, Boysenberry, Lemon, Tamarind.

(iii) Stem Cuttings. They are used in horticulture for vegetatitive propagation of a number of plants,e.g., Bougainvilea, Duranta, China Rose, Clerodendron, Cirus, Rose, Tea, Coffee, Grape. 20—30 cm longpieces of one year old stems with intact buds are first treated with root inducing hormone in the basalregion and then planted in the soil in their natural position. Roots develop at the base. New shoots developfrom the buds.

3. Layering. It is horticultural technique of vegetative propagation in which a soft one year old shootis first induced to develop roots and then cut off to form new plant. It is also, therefore, called rooting-cutting (Hartmann et al, 1997). The timing is early spring or rainy season. A middle part of the shoot isdefoliated and given a small injury in the form of ringing (removal of bark in the form of a narrow ring),notching (a narrow V-like cut) or tongueing (tongue-like cut). It is then buried and pegged down in the soilwith the foliage bearing apical part remaining above ground in near vertical position. The injured peggeddown shoot is called layer. As the roots develop in the injured region, the layer is cut off and planted as anew plant. Layering is of several types :

(i) Simple Layering. A basal branch is inujured and pegged down at one place to form a layer, e.g.,Jasmine (Fig. 1.13), Grape vine.

(ii) Serpentine Layering. A long pliable basalbranch is injured at intervals. Then injured parts areburied and pegged in soil forming a serpentine layer.As the injured parts develop roots, a number of newplants are cut off from a single layer, e.g., Clematis.

(iii) Mound (or Stool) Layering. The shoot systemis pruned. The basal part develops a number of shoots.Their lower parts are buried in a mound of soil andsaw dust. After some time roots develop from thebasal parts of the new shoots. They are then separatedand planted, e.g., Currant, Quince, Cherry.

(iv) Trench Layering. A shallow narrow trenchis dug along a plant. A branch is pegged horizontallyin the trench and then covered with soil. A number

of vertical shoots grow from the trench layer. They

are separated and planted, e.g., Mulberry, Walnut.

�Fig. 1.13. Simple layering in Jasmine.

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4. Gootee (Air Layering, Fig. 1.14). A healthy woodyaerial shoot well above the ground level is selected. A3—5 cm long ring of bark is removed from near its base. Itis plastered with grafting clay. Grafting clay consists ofhay, cowdung, clay (1 : 1 : 2) made into paste with water.Small quantity of IBA or NAA may be added to enhancerooting. Polythene is wrapped over plastered area to preventdrying out of grafting clay. Roots develop from above thegirdled area. The shoot is now cut below the plastered areaand planted e.g., Pomegranate, Litchi, Lemon.

5. Grafting. It is a technique of forming a superiorcomposite plant by joining a shoot system of a superiorhigh yielding variety with the stronger and efficient rootssystem of generally a local variety. Grafting can be undertaken only in those plants which possess cambium,i.e., woody dicots and gymnosperms. The selected shoot is called scion (or graft) while the selected rootsystem is known as stock. Shoot system of the stock is cut down some 10–30 cm above the base of the root.All the buds and the leaves present on the stump are removed. Complementary cuts are given to both stockand scion. The scion is inserted over the stock in such a way that the cambia of the two come together. Theunion is covered by grafting wax and bandaged. Grafting is successful if the scion starts bearing new leavesand branches. Some common examples of plants on which the grafting is used are Mango, Guava, Pine,Peach, Apple and Pear. Depending upon the type of union between scion and stock, grafting is of severaltypes.

(i) Tongue (Slice or Whip) Grafting. Scion and stock are of the same diameter. The two are givencomplementary oblique sloping cuts.

(ii) Wedge Grafting. Scion and stock are of the same diameter. Scion is given wedge shaped cut whilestock is given V-shaped cut.

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�Fig. 1.15. Some types of stem grafting.

(iii) Crown Grafting. Scions is narrow while the stock has a large diameter. Scions are given wedgeshaped cuts. Stock is given slit-like cuts on the sides. Two or more scions are fitted into stock andbandaged.

(iv) Side Grafting. Scion is narrow while stock is broader. Stock is given a V-shaped notch on oneside. Scion is given an elongated oblique wedge-shaped cut for fitting into side notch of the stock.

�Fig. 1.14. Gootee.

�� (v) Approach Grafting. It is carried out between two independently growing plants. The shoots of the

two plants are sliced for a distance of 2·5—5·0 cm at the same level (splice approach grafting). They canalso be given complementary oblique sloping cuts (tongue approach grafting) or vertical cuts (inlay approachgrafting) in case the stock is broader. The two are attached and bandaged in the region of cuts. When thegraft is established, the stock is cut above the region of union while scion is cut below the same.

6. Bud Grafting. Here scion is a bud taken from thesuperior variety. It has both cambium and a small piece of bark.The stem of the stock is given a T-shaped cut a few centimetresabove the soil so as to reach upto its cambium. The bark islifted from the sides of the T-shapted cut. The bud scion isinserted in the lifted part of the bark and the latter is allowed tocover the sides of the bud. Grafting wax is applied to the joint.The joint is then bandaged. Bud sprouts after 3—5 weeks whenorganic union has been established. Upper part of the stock iscut. The buds and leaves of the stock present below the joint areremoved. Bud grafting is commonly practised in Rose. Evenbuds of more than one variety can be grafted on the same stock but on different branches to produce flowersof different types on the same plant. Bud grafting is also carried out in Apple and Peach.

7. Micropropagation or Tissue Culture. It is the practice of rapidly multiplying stock plant material,dividing it into many parts and producing a large progeny of plants. This is carried out with the help oftissue culture technique in a germ free environment. The plants formed through micropropagation are virusfree and clone of the plant from which explant was obtained.

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1. There are some plants which multiply only through vegetative means. Such plants lack sexual reproductionso that seeds are not formed, e.g., Banana, Sugarcane, Pineapple, Seedless Orange, Seedless Grape.

2. Plants with reduced power of sexual reproduction are commonly multiplied vegetatively, e.g.,Cynodon dactylon (Lawn or Bermuda Grass).

3. Plants with long seed dormancy or poor seed viability are multiplied easily through this method.

4. It helps in covering a denuded area quickly.

5. It overcomes difficulty of establishment of plants in new areas where propagation through seeds oftenfails.

6. It is a quicker method of multiplication requiring far less time than the one taken through sexualreproduction. Potato crop is ready after three months if grown through tubers while it takes 13—15 monthsif raised through seeds. Similarly, lilies mature after 1—2 years if grown vegetatively and 4—7 years ifgrown through seeds.

7. Survival rate of plants is nearly 100% as compared to less than 1% through seeds.

8. It can preserve good qualities of a variety, race and species indefinitely.

9. Superior varieties with poor root system can be propagated through grafting.

10. Grafting helps in combining good traits of two or more varieties into a single composite plant.

11. It reduces the period required for flowering and fruiting of plants.

12. Some common infections can be rectifed through pruning and micrografting.

13. The yield is of uniform quality as variations do not develop in the absence of gene recombination.

��1. Dispersal is nearly absent.

�Fig. 1.16. Bud Grafting.

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�� "2. Vegetative propagation causes overcrowding. It results in severe competition amongst the daughters.

3. Vegetative propagules cannot be stored for long.

4. Vegetative propagules are prone to infections, desiccation and decay as they are not protected anddehydrated like seeds.

5. Variability and adaptability are absent.

6. Repeated vegetative propagation brings about degeneration of the variety and race.

7. There is no mechanism to introduce good traits or eliminate bad traits.

8. A disease present in the parent plant spreads to all the daughters.

�#�# $�%&' �$(��)%�*��+It is the phenomenon of formation of young ones or offspring through the process of formation of haploid

gametes, their fusion and the growth of resultant diploid zygotes. Sexual reproduction is also calledsyngenesis (Gk. syn—together, genesis—origin), amphimixis (Gk. amphi— both, mixis—union) or amphigony.As compared to asexual reproduction, it is more elaborate, complex but slow process.

"�� #!�� $�� 1. Parents. In most animals and some plants, sexual reproduction is biparental with two types of

sexually mature individuals, male parent and female parent. Most plants and some lower animals arehermaphrodite. They, however, avoid self fertilization in most of the cases.

2. Sex Organs. There are two types of sex organs, male and female.

3. Meiosis. It occurs once in the life cycle of all sexually reproducing organisms. Meiosis is a means ofmaintaining the fixed chromosome number of the species. Chromosome number gets doubled at the time offertilization. In the absence of meiosis, chromosome number would become unmanageable within a fewgenerations. Meiosis is, therefore, necessary.

However, it may occur at the time of gamete formation (gametic meiosis), germination of zygote(zygotic meiosis) and formation of haploid spores (sporic meiosis). Except for gametic meiosis (e.g., mostanimals), gamete formation involves mitotic division (e.g., Ulothrix, Fern).

4. Gametes. Gametes are the sex cells which take part is sexual reproduction. They are alwayshaploid. Gametes are structurally similar in lower organisms. They are, however, functionally different inmost cases. Gametes are differentiated into male and female in animals and plants. Male gametes areproduced in larger number as compared to the female gametes. The male gametes are motile. They arecalled sperms or spermatozoids. Female gametes are often large and non-motile. They are called eggs orova. Differentiation of gametes is also related to differentiation of sex organs and the differences in thebodies of males and females.

5. Fertilization. The two types of haploid gametes fuse. The act is called fertilization. The place offertilization depends upon the type of organism and its habitat. Fertilization produces diploid zygote.

6. Zygote. It is a single-celled diploid structure from which new individual develops through repeatedcell division and differentiation.

7. Juvenile Phase. The new individual formed from a zygote does not develop the power of gameteformation immediately. It passes through a non-reproductive phase called juvenile phase.

8. Specializations. A number of specializations develop in the individual during sexual maturation. Thisconsumes a lot of resources of the individual.

9. Slower Process. Sexual reproduction is a slower process as compared to asexual reproduction. Thenumber of offspring is also smaller.

10. Alternation of Phases. The life cycle consists of alternation of haploid and diploid phases.

11. Variations. A number of variations appear in the offspring. Variations develop due to (i) Crossing over duringmeiosis. (ii) Chance separation of chromosomes during meiosis. (iii) Chance combination of chromosomes duringfertilization. (iv) Mutations. Despite variations the offspring broadly resemble the parents.

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Organisms spend a lot of their resources and energy in the formation of sex organs, sex cells, theirfertilization and development of young ones in order to provide some benefits for their race.

1. Flow of Genes in Population. There is flow of genes amongst individuals of a population duringsexual reproduction. New mutations or variations do not remain restricted to a few individuals. Theyultimately pass into the whole population through sexual reproduction.

2. Vigour and Vitality. Mixing of genes during sexual reproduction maintains the vigour andvitality of the entire population.

3. Variations. Because of sexual reproduction, no two individuals are exactly similar. The differenceshelp in recognition of the individuals. Variations developed during sexual reproduction providecompetitiveness to individuals. They have adaptability to changes in environment.

4. Evolution. Variations produced in sexual reproduction form the basis of evolution.5. Caring of Young Ones. By instinct or by natural evolution, the young ones produced during sexual

reproduction are protected during their vulnerable stages. It is carried out by parental care in most animals.Protection is also provided during early growth in most plants prior to their establishment as new individuals.

�� (i) It is a very slow process.

(ii) It requires a lot of resources.(iii) Sexual reproduction is commonly biparental.(iv) Fertilisation has a chance factor.(v) A large number of young ones die due to poor genetic make up in face of high level of

competition.

Differences in Progeny of Asexual and Sexual Reproduction

S.No. Progeny of Asexual Reproduction Progeny of Sexual Reproduction

1. It is genetically uniform. Variability occurs amongst the offspring.2. The progeny is the clone of the parent. The progeny is different from either of the two parents3. There is a single parent. Generally, two parents are involved.4. Daughters are formed from a special- Sexual reproduction involves the formation and

ised or unspecialised part of the parent fusion of gametes.Gametes are not involved.

5. There is little adaptability to changes Adaptability to changes in environment is present.in environment.

6. The young ones get established quickly. The young ones take longer time to establish.

�� $�Sex originated in protistans and simple algae (e.g., Chlamydomonas, Ulothrix). These organisms

multiply asexually during favourable conditions. The gametes are formed towards the approach ofunfavourable conditions. The gametes fuse and form zygote which often develops a thick wall to becomeperennating zygospore. Zygospore germinates under favourable conditions to form the protist/alga thatrepeats the cycle. In Chlamydomonas and Ulothrix the zoospores and gametes are structurally similar.Single gametes, if provided with favourable conditions can sometimes grow to form new individuals.The only difference between gametes and zoospores is in size and environmental conditions. Underunfavourable conditions the propagules are unable to grow and produce new individuals. They are sluggishand tend to remain together. Circumstances in the remote past helped them to fuse. Fusion in pairs provedhighly beneficial as it pooled their resources, genetic potentialities and allowed them to perennate. The act

�� -of formation and fusion of weak propagules stayed and established in the life cycle permanently in allsubsequently evolved organisms. It is called hunger theory of sex.

Early gametes were similar or isogametes. Sexual reproduction was isogamous (homogamety). Later onevolution occurred giving rise to anisogamy and oogamy (heterogamety). Similarly, sex organs evolvedwhich differentiated into male and female paving way for differentiation of male and female individuals.While early evolution of sex depended upon environment, later on hormones began to play the role ofdeveloping various phases in the life cycle of individuals.

�!�� '� � #&��In relation to reproduction, life cycle of an individual is divisible into three phases—juvenile, reproductive

and senescent. The transition from one phase to the other is controlled by hormones. Interaction ofhormones and certain environmental factors regulate reproduction and associated behaviour changes.

1. Juvenile Phase (Juvenility)

It is prereproductive period in the life cycle of an individual. The period is characterised by rapidgrowth. All the resources are used up in growth and development of the body. The juvenile phase mayhave different structures, e.g., different shapes of leaves, different plumage (in birds), different protectionsof the body. Juvenile phase is called vegetative phase in plants. The duration of juvenile phase variesfrom organism to organism.

2. Reproductive Phase (Maturity)

It is the phase of life cycle wherein individuals have the potential to reproduce. The early period ofreproductive phase is called puberty. Sex organs develop and mature during puberty. Growth is sloweddown. In higher plants, appearance of flowers is indication of sexual maturity. Sexually, there are twotypes of flowering plants, monocarpic and polycarpic.

Differences Between Juvenile and Reproductive Phases

S.No. Juvenile Phase Reproductive Phase

1. It is early phase of life cycle It is the middle phase of the life cycle.

2. It is period of rapid growth. Growth is either slow or absent.

3. Juvenile phase is often the phase It has attained a permanent shape and size.

of changing shape and size.

4. The phase is devoid of functional The phase is characterised by presence of functional

sex organs. sex organs.

5. Individuals in the juvenile phase Individuals of the reproductive phase are sexually

are not active sexually. active.

Neoteny and Paedogenesis. Retention of larval characters even in the sexually mature individual or

development of adult characters by a larval form is called neoteny (Gk. neos—young, temein—to

stretch), e.g., axolotl larva of Salamander Ambystoma. Paedogenesis (Gk. pais—child, genesis—

descent) is reproduction in the young or larval stage, e.g. axolotl.

Monocarpic Plants. They flower only once in their life after which they bear fruits and die. Both

annual (e.g., Sunflower, Rice, Wheat) and biennial (e.g., Henbane, Radish) are monocarpic in nature.

Some perennial plants are also monocarpic. Bamboos (e.g., Bambusa tulda, Melocanna bambusoides)

remain vegetative for 50–100 years. They, then flower, fruit and die. Monocarpic plant of Strobilanthes

kunthiana (vern. Neelakuranji) has a life span of 12 years. In the twelfth year, it flowers, fruits and dies. The plant

came to flower in September-October 2006 and now in August to October in 2018. The flowering converts large

hilly tracts of Kerala, Karnataka and Tamil Nadu into blue stretches that attract a large number of tourists.

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Biennial Plants

The plants complete their life cycle in twogrowing seasons.

The plants remain vegetative in the first growingseason. They become reproductive in the secondgrowing season.

Ex. Henbane.

Differences Between Annual and Biennial Plants

S.No. Annual Plants

1. The plants complete their life cycle inone growing season.

2. Vegetative phase is immediately followedby reproductive phase.

Ex. Sunflower.

Polycarpic Plants. They are perennial plants which after reaching maturity flower every year in

particular seasons, e.g., Mango, Apple, Jackfruit, Grape vine, Orange. Very few perennial plants bear

flowers throughout the year, e.g. China Rose (Shoe Flower). Interflowering period of polycarpic plants is

used for building up resources and is therefore a recovery phase. It is not juvenile phase but is part of the

mature phase.

Differences Between Monocarpic and Polycarpic Plants

S.No. Monocarpic Plants Polycarpic Plants

1. The plants flower only once. The plants flower repeatedly at intervals.

2. Monocarpic plants die after flowering They are not killed after flowering and fruiting.and fruiting.

3. Plants are generally annual or biennial. The plants are perennial.

Very few monocarpic fruits are perennial.

4. The reproductive phase is short but continuous. The reproductive phase is prolonged and interruptedby interflowering or recovery phases.

Animal Breeding. On the basis of periodicity of breeding, animals are of two types, seasonal and

continuous breeders. Seasonal breeders reproduce only at particular period of the year, e.g. frog, lizards,

most birds, deer. Continuous breeders continue to breed throughout their span of sexual maturity, e.g.

cattle, poultry, mice, rabbit, honey bee queen. Birds are commonly seasonal breeders. However, in

captivity some of them have become continuous breeders, e.g., poultry birds. In poultry farms, hens continueto lay unfertilised or vegetative eggs throughout the year. It is a commercial exploitation of faculty ofreproduction for human welfare.

In placental mammals, the females show cyclic changes in the activities of ovaries, accessory ducts andhormones throughout their reproductive phase. There are two types of cycles, menstrual and oestrus.

Menstrual Cycle. It is a series of cyclic changes that occur in ovaries, reproductive tract and hormonesecretions of female primates (monkeys, apes and humans) from puberty to menopause. There is a regularsloughing off of inner lining of reproductive tract-uterus which is passed alongwith some blood as menstruation.An excessive sex urge is absent in any part of menstrual cycle. The periodicity of cycle is a lunar month.

Oestrus Cycle (= Estrus Cycle). It is a series of cyclic changes that are found in the ovaries,reproductive tract and hormones of female nonprimate mammals, e.g., cows, dogs, cats, horse, buffalo. Thereis period called oestrus (= estrus, Gk oistros - maddening desire) when the female has a very high blood titreof oestrogens and develops a strong sex heat. During this period the female receives the male. Oestrus lastsfor 18 hours in Cow, about a week in dog and cat. At the end of oestrus, the lining of reproductive tract issloughed off. However, there is no menstruation. The sloughed off tissues are absorbed. Oestrus is followed bya passive period called anoestrus. It may vary from a few months to more than a year. Deer is called

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Menstrual Cycle

The interval between two successive cycles isabout four weeks.

Menstrual cycle has three phases-menstruation,proliferative and secretory.

There is no such irresistible sex urge.

Female does not permit sex duringmenstruation.Blood loss occurs during menstruation.

It is expelled during menstruation.

It occurs in female primates.

monoestrous because it experiences oestrus once a year. Dogs are bioestrous as they experience twooestruses in a year. The term polyoestrous is used for a succession of periods of oestrus in one year or onebreeding season, e.g., cat, cow, pig, horse, sheep, goat. Polyoestrous Mouse has many oestruses in a year.

Deer and dogs are seasonal breeders as they develop the urge for sexual reproduction only during particular

favourable periods. Mouse is a continuous breeder as it remains reproductively active throughout the year.

Differences Between Oestrus and Menstrual Cycles

S.No. Oestrus Cycle

1. The interval between two successivecycles varies between a few months toover a year.

2. Oestrus cycle has two phases, oestrusand nonestrus.

3. The female develops a strong irresistibleurge for sex during oestrus.

4. The female does not permit sex outsidethe oestrus.

5. There is no blood loss.

6. The sloughed off lining of reproductivetract is reabsorbed.

7. It occurs in female nonprimates.

3. Senescent Phase ( Senescence, Ageing)

End of reproductive phase or beginning of the post reproductive phase is accompanied by deteriorationof structure and physiology of the body. The phenomenon is called ageing or senescence. The efficiencyof all body organs and tissues (e.g., kidneys, lungs, heart, brain, eyes, blood volume, muscles)decreases. Chances of catching diseases and developing deformities increase so that natural death may

occur due to defunctioning of any vital organ.

��$� ��$�()�'��)#��Structures associated with sexual reproduction are different in different types of organisms. Events in

sexual reproduction are also elaborate and complex. However, they have a fundamental similarity in thatsexual reproduction involves formation of gametes, transfer of gametes, fusion of male and female gametesand embryogenesis. The sequential events have been grouped into three stages – prefertilization, fertilizationand post-fertilization events.�#�#�# (��/0��1�� $2��

They are the events in sexual reproduction which occur prior to the process of fertilization. Mainprefertilization events are two, gametogenesis and gamete transfer.�#�#�#�# 3��(Gk. gametos—gamete, genesis—production)

Gametogenesis is the process of formation and differentiation of haploid sex cells or gametes. Insexually reproducing lower organisms like simple algae, the gametes are structurally and functionallysimilar. They are called isogametes or homogametes, e.g., Cladophora, Ulothrix. Such gametes arenormally flagellate or planogametes. In Spirogyra the isogametes are nonflagellate or aplanogametes. Theyare also structurally similar but are physiologically different and are called physiological anisogametes. InChlamydomonas braunii the gametes are morphologically similar but differ in size. They are known asanisogametes. In most of the sexually reproducing organisms, the gametes are of two morphological distincttypes, female egg or ovum and male sperm or antherozoid (= spermatozoid) e.g., Volvox, Fucus (a brownalga), bryophytes, pteridophytes, humans. Such morphologically distinct gametes are called heterogametes.The phenomenon of having morphologically and physiologically different gametes is called heterogamety.

�� The male gamete, sperm or antherozoid is motile. It generally possesses one or two flagella for swimmingupto the female gamete. In seed plants, male gametes are devoid of flagella because they are carried to femalegametes by pollen tubes. The female gamete, egg or ovum, is generally large food laden and nonmotile. Theunion between a large nonmotile egg and a small motile gamete is called oogamy. As the male gametes areto search for and reach the female gametes, they are always produced in very large number.

Differences Between Homogamety and Heterogamety

S.No. Homogamety/Isogamy Heterogamety/Anisogamy

1. The fusing gametes are similar. The fusing gametes are dissimilar.

2. The compatible gametes cannot be differen- The compatible gametes differ in their structure,tiated morphologically or physiologically. function or both.

3. The gametes cannot be categorised into male The gametes can be categorised into male andand female. female.

4. Both the gametes are equally active. The male gametes are more active.5. There is no difference in content of stored The female gametes are richer in stored nutrients.

material (nutrients).6. Homogametes commonly occur in primitive It occurs in more advanced aquatic as well as

aquatic organisms. terrestrial organisms.

7. Both the gametes are produced in equal number. The male gametes are produced in very largenumber as compared to female gametes.

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�Fig. 1.17. Types of gametes. A, isogametes of Cladophora. B, anisogametes of Chlamydomonas braunii.C, heterogametes of Fucus. D, heterogametes of humans.

Sexuality in Organisms. In most primitive sexually reproducing organisms, the functional gametesbelong to the same or single parent. There is no morphological or physiological difference. These organismsare called homothallic, e.g., Mucor mucedo. The functional gametes belong to genetically different parents inRhizopus stolonifer, though there is no morphological or physiological difference. Such organisms are calledheterothallic. In higher organisms, sex organs developed and got differentiated into male and female. In mostflowering plants, both the types of sex organs (stamens and carpels) occur in the same flower. They are calledhermaphrodite or bisexual. In some flowering plants, there are distinct male or staminate flowers andfemale or pistillate flowers. In Cycas (a gymnosperm), Vallisneria, Date Palm and Papaya (angiosperms) themale and female flowers are borne on different plants. They are called dioecious plants. Cucurbits, Coconutand Maize possess both male and female flowers on the same plants. They are called monoecious plants. Thecondition of monoecious and dioecious nature is also found in lower plants. Chara often bears both male(antheridium) and female (oogonium) sex organs on the same plant. It is, therefore, monoecious. Marchantia, aliverwort, is dioecious. Here, the male plant bears antheridia over a special structure called antheridiophore.The female plant similarly possesses archegonia over a special structure known as archegoniophore.

All higher animals are unisexual with distinct male and female individuals showing exogamy or crossfertilization. However, in some lower animals, both the types of sex organs are present in the sameindividual. These animals are called hermaphrodite or bisexual, e.g., Sponge, Tapeworm, Leech, Earthworm.

�� Some of them show endogamy or self-fertilization (e.g., Taenia) while others show exogamy or crossfertilization (e.g. Earthworm) due to reproductive organs maturing at different times.

Differences Between Monoecious and Dioecious Plants

S.No. Monoecious Plants Dioecious Plants

1. Both the types of flowers occur in the same The two types of flowers are found in different

individual. plants.

2. It prevents autogamy but not geitonogamy. It prevents both autogamy and geitonogamy.

Example : Castor, Maize Example : Papaya.

Cell Division During Gamete Formation. Gametes are always haploid whether the cells or structuresproducing them are haploid or diploid. The fusion product of gametes is always diploid whether the matureindividual developed from the fusion product is haploid or diploid. It is because meiosis occurs in the life ofall sexually reproducing organisms that reduces the chromosome number to half. The cells which undergomeiosis to produce haploid structures are called meiocytes. They are always diploid. Crossing-over occursduring meiosis. It introduces recombinations or variations. Depending upon the stage at which meiosisoccurs, the latter is of three types.

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�Fig. 1.18. Diversity in sexuality of organisms. A, bisexual or hermaphrodite animal Earthworm.B, unisexual animal Cockroach. C, monoecious plant Chara. D, dioecious plant Marchantia.

E, bisexual flower of Sweet Potato.

(i) Zygotic Meiosis. Meiosis occurs during the development of zygote, i.e., zygote functions asmeiocyte. It produces haploid organism, e.g. Ulothrix, Chlamydomonas. Here only mitotic divisions occurduring the differentiation of gametes.

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(ii) Sporic Meiosis. It occurs in most plants. Here meiosis takes place inside sporangia. In seed plantssporangia are of two types, microsporangia and megasporangia. In seedless plants, sporangia are ofgenerally one type. Meiocytes occur inside sporangia. Their meiosis produces haploid spores. On germination,haploid spores or meiospores produce haploid bodies called gametophytes. Gametes develop in them onlythrough mitotic divisions.

(iii) Gametic Meiosis. It occurs in animals. Their bodies and sex organs are diploid. The germinalcells which give rise to gametes are also diploid. They functions as meiocytes (gamete mother cells),undergo meiosis and produce haploid gametes.

Whether the parent is haploid or diploid, gametes are always haploid, i.e., they possess only one set ofchromosomes or genome.

Table 1.1. Chromosome Number in Meiocytes (diploid, 2N) and Gametes (haploid, N) of some Organisms

S.No. Name of Organism Meiocyte (2N) Gamete (N)

1. Humans 46 23

2. Housefly 12 6

3. Rat 42 21

4. Dog 78 39

5. Cat 38 19

6. Fruitfly 8 4

7. Ophioglossum (a fern) 1260 630

8. Apple 34 17

9. Rice 24 12

10. Maize 20 10

11. Potato 48 24

12. Butterfly 380 190

13. Onion 16 8

�#�#�#�# 3�� *��!��It is the bringing of compatible gametes near each other. Aquatic organisms shed their gametes in

water. In case of isogametes as found in some algae and fungi, both the types of gametes are motile andattract each other. In case of heterogametes, there are stationary non-motile female gametes and motilemale gametes. In bryophytes and pteridophytes ova occur inside archegonia. The sperms are motile. Theyrequire a thin film of water to swim upto open archegonia where an attractant is being released. However,a number of male gametes fail to reach the ova. Therefore, the number of male gametes is always severalthousand times the number of female gametes. For a single ovum in humans, the number of male gametes is100-400 millions.

In flowering plants, pollen grains carry the male gametes. They are formed in large number. They aretransferred to stigma of the female organ or carpel through the process of pollination. Pollination precedesfertilization. It is of two types, self pollination and cross pollination. In self pollination, the pollen grains of ananther are transferred to the stigma of the same bisexual flower. It occurs through mechanical movement inthe bud condition of Pea and Wheat. In cross pollination, that occurs in both bisexual and unisexual flowers,the pollen grains are carried to the stigma of other flowers through the agency of wind, water or insects.Pollen grains germinate over the stigma and produce pollen tubes. Pollen tubes carry the male gametes to theovules and burst open to release male gametes near the female gamete or egg.

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�Fig. 1.19. A, homogametic contact in alga. B, pollen grains germinating over stigma.

Most animals are dioecious or unisexual. They perform cross fertilization (exogamy) or union ofgametes belonging to different parents (biparental). In aquatic habitats, they commonly shed the gametesnearby to increase the chances of fusion. In terrestrial habitats, the animals have evolved varioustechniques for gamete transfer. Even many monoecious or bisexual animals prefer cross fertilization(exogamy) and have developed mechanism for gamete transfer. Self fertilization (endogamy) is thefusion of gametes belonging to the same parent (uniparental). In Taenia, where self-fertilization orendogamy occurs, male gametes are transferred from one proglottid to another. Successful transfer andcoming together of the two types of gametes is essential for fertilisation.

Differences Between Self Fertilization and Cross Fertilization

S.No. Self Fertilization (Endogamy) Cross Fertilization (Exogamy)

1. The fusing gametes belong to the same parent. The fusing gametes belong to different parents.2. It occurs in hermaphrodite individuals. It can occur in both hermaphrodite and

unisexual individuals.3. It increases homozygosity. It maintains heterozygosity.4. Self fertilization does not introduce new traits It introduces new traits.

or variations.5. It is rare amongst animals. It is very common amongst animals.

Examples. Taenia, Fasciola Examples. Frog, Cockroach.

�#�#�# 0$�*�'� &*��+Events leading to coming together and fusion of two compatible gametes to form diploid zygote is

called fertilization. The process of fusion of gametes is called syngamy (Gk. syn– together, gamos–marriage). The two terms of syngamy and fertilization are, however, often used interchangeably.

Differences Between Syngamy and Fertilization

S.No. Syngamy Fertilization

1. It is part of the process of fertilization. It is an act comprising syngamy as a component.

2. It is fusion of two compatiable gametes It is a set of events that leads to syngamy.

forming a diploid zygote.

Where does Syngamy Occur ? Depending upon the place of syngamy; fertilization is of two types,external and internal.

External Fertilization. It is syngamy that occurs outside the body of organisms. It usually takes place inaquatic medium. External fertilization is common in most algae, some fungi, several invertebrates, bony fishesand amphibians. The organisms performing external fertilization show great synchrony in the release ofcompatible gametes into the external medium for enhancing the chances of syngamy. Since it involves achance factor, the number of gametes of both the types is generally large. As a result, the number of offspringis also very high. They are, however, extremely vulnerable to predators for their survival upto adulthood.

�� Internal Fertilization. It is syngamy or fertilization that occurs inside the body of the organisms. It is

common in terrestrial organisms but some aquatic and semiaquatic organisms also perform internalfertilization, e.g., fungi, reptiles, birds, mammals, sharks (cartilaginons fishes), bryophytes, pteridophytes,gymnosperms and angiosperms. Egg remains in the body of the female. The male gamete reaches thereto fertilize the same. In animals and seedless embryophytes, the male gametes are motile. They swim upto the female gamete to fertilize it. In seed plants, the male gametes are nonmotile. They are carried tothe female gamete by means of pollen tube. Since internal fertilization is a sure method, the number offemale gametes and hence the number of offspring remains small.

Differences Between External and Internal Fertilization

S.No. External Fertilization Internal Fertilization

1. Syngamy occurs in the outside medium. Syngamy occurs inside the body of an organism.2. Both the types of gametes are discharged. Only the male gametes are discharged.3. It is not a very sure method of fertilization. It is a comparatively surer method.4. The young ones develop unprotected in the out-. The young ones are well protected during

side medium.They are vulnerable to predators. their early development.5. The number of young ones is very high. The number of young ones is small.6. Both the types of gametes are produced is large The female gametes are produced in small

number. number.

��!�� (Gk. parthenos—virgin, genesis—production)

It is uniparental sexual reproduction in which a new individual develops from a single unfused gamete,commonly the female or egg in animals. The young ones resemble the mother in all inherited characters.Parthenogenesis was discovered in animals by Charles Bonnet (1745) when he found that unfertilised eggs ofaphid could develop into young ones which resembled the mother in all aspects. The term was coined byRichard Owen (1848). Parthenogenesis occurs in rotifers, many arthropod crustaceans, arachnids, insects (e.g.,Honey Bees), gastropod molluscs, some lizards and birds (e.g., Turkey). Parthenogenesis can be natural orartificial. On the basis of sex of the new individuals, parthenogenesis is of three types. (i) Arrhenotoky (Gk.arrhen—male, tokos—birth). This type of parthenogenesis produces male individuals. The same aregenerally haploid. Arrhenotoky occurs in rotifers, some spiders, Tick, Mite, Wasp and HoneyBee. (ii) Thelytoky (Gk. thelys—female, tokos—birth). Parthenogenesis produces female individuals. Itoccurs in Typhlina brahmina and Lacerta saxicola-armeniaca. (iii) Amphitoky (Gk. amphi—both, tokos—birth). Both male and female individuals are produced parthenogenetically. Amphitoky occurs in aphids after afew cycles of thelytoky.

�� !��It is parthenogenesis which occur naturally in certain animals due to innate or internal reasons. Natural

parthenogenesis is of three types—obligatory, cyclic and paedogenetic.

1. Obligatory or Complete Parthenogenesis. Parthenogenesis is the only mode of reproduction asmales are absent in the population. Due to absence of males, sexual cycle cannot be completed. Youngones are also females. They develop directly or parthenogenetically from the eggs, e.g., Rotifer(a Wheel Animal), Typhlina brahmina (a small lizard, about 15 cm in length), Lacerta saxicola-armeniaca (Caucasian Rocklizard), Cnemidophorus species (Whiptail Lizards of America).

2. Periodic, Cyclic or Incomplete Parthenogenesis. Parthenogenesis occurs alongwith sexualreproduction. Fertilised eggs and parthenogenetically developed eggs give rise to different castes. (i) InHoney Bee, fertilised eggs form females (one fertile queen and other sterile workers) whileparthenogenetically eggs form males or drones. (ii) During spring-summer period aphids produce anumber of generations of females through parthenogenesis. Towards the end of summer both males and

�� "females are formed which mate and produce fertilised eggs for maturation into females during next spring.(iii) Some wasps show alternate parthenogenetic and sexual generations. (iv) In Turkey, the males candevelop parthenogenetically due to chromosome doubling in egg.

3. Paedogenetic Parthenogenesis. In Gall Fly, the larvae may lay eggs which develop parthenogeneticallyto form more larvae. In liver fluke, sporocyst larva forms redia, redia forms more rediae which then giverise to cercariae.

Advantages. (i) Parthenogenesis determines sex in some cases, e.g., Honey Bee (male or drone)(ii) It allows multiplication and perpetuation of those populations in which the males are absent, e.g.,Typhlina brahmina. (iii) It allows multiplication of those genetic systems where haploid-diploid alternationis not possible, e.g., aneuploid, triploid. (iv) Parthenogenesis is a method of rapid multiplication, e.g.,aphids. (v) It is simpler and economical than sexual reproduction. (vi) The progeny resembles theparents in all aspects.

Disadvantages. (i) Meiotic crossing over is absent. Therefore, new linkages are not established.(ii) Recombination of alleles as found in sexual reproduction, is absent. (iii) There is little variation andhence adaptability in the population ; always posing a danger of extinction.

�#�#�# (� */0$�*�'� &*��+ $4$+* They are the events that occur after syngamy or formation of zygote.

�#�#�#�# *5� 6��It is universally the first cell of the new generation in all sexually reproducing organisms. Zygote is

always diploid. It is formed in the external aquatic medium in those organisms which perform externalfertilization. Zygote is produced in the body of the female in cases where fertilization is internal.

(i) In many algae and fungi, the zygote secretes a thick wall and gives rise to perennating sporecalled zygospore. Zygospore germinates during next growing season. It undergoes meiosis. The productsof meiosis form haploid individuals. This leads to haplontic life cycle.

Differences Between Zoospore and Zygote

S.No. Zoospore Zygote

1. It is a motile structure. It may be motile or non-motile.2. Zoospore takes part in dispersal. Zygote has little role in dispersal.3. It helps in asexual reproduction. Zygote is a product of sexual reproduction.4. It may be haploid or diploid. It is always diploid.5. It is formed through mitosis. It develops through fusion of two gametes.6. It does not cause variations. It brings about a lot of variations.

(ii) In most animals, diploid zygote does not take rest. It continues growth and division, firstforming an embryo and then the whole individual which is diploid. It leads to diplontic life cycle.

(ii) In most plants, zygote first forms an embryo and then the diploid sporophyte. The sporophytebears sporangia where meiosis occurs to form haploid spores. The latter produce haploid gametophytes.Gametes are borne in the specialised structures or gametangia of the gametophytes. The life cycle ishaplodiplontic or diplohaplontic.

�*��1. Zygote is a vital link between two successive generations.

2. It ensures the continuity of race from generation to generation.

3. The body of all multicellular organisms develops from the single–celled zygote. All the cells of thebody, therefore, contain the same genetic traits as are present in the zygote.

4. It carries genomes from two different organisms and is, therefore, always hybrid in nature and full ofvariations.

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�#�#�#�# $�7��Embryogenesis (Gk. embryon—embryo, genesis—descent) is the process of development of embryo

from zygote. The term blastogenesis is used for development of new individuals from buds, fragments andother asexual propagules. Embryo is a multicellular stage in the life cycle of a plant or animal prior toformation of an independent individual. In embryogenesis, the zygote undergoes repeated cell divisionsthrough mitosis. The divisions help in growth of the embryo. Cells undergo differentiation attainingspecific shape, size and function. Cell differentiation occurs at specific locations resulting in production ofdifferent tissues, organs and organ systems. Development of different external and internal structures iscalled morphogenesis.

Differences between Gametogenesis and Embryogenesis

S.No. Gametogenesis Embryogenesis

1. Gametogenesis is formation of It is formation of a young individual from zygote.gametes.

2. It is a pre-fertilization event. It is a post fertilization event.

3. It produces haploid gametes. It gives rise to diploid embryo.

4. Gametogenesis occurs inside sex organs. It occurs outside or inside the body of the female.

5. Meiosis occurs during or prior to Meiosis does not occur during embryogenesis.

gametogenesis.

��&��&Depending upon the site of development of embryo, animals are of three types—oviparous, ovoviviparous

and viviparous. Their habits are respectively called ovipary, ovovivipary and vivipary. (i) Ovipary is thedevelopment of embryo inside the egg but outside the body of the female. The phenomenon occurs in egglaying animals, e.g., Frog, birds, reptiles, prototherians, several fishes, arthropods. The eggs are generallycovered by hard calcareous shell and laid in a safe place. They are often incubated. However, the eggs andtheir contained embryos are exposed to harsh external environment and predators. Parental care andprotection of young ones are less efficient. (ii) Ovovivipary is the phenomenon of female retaining the eggsafter fertilisation and allowing the development of embryo inside the body but without providing any otherextra nourishement as the placenta is absent. The female animals, however, give birth to the young ones,e.g., Sharks, Rattle Snake. (iii) Vivipary is both fertilisation and development of embryo inside the body offemale with ensured nourishement for growing embryo by forming placenta. The animals give birth to theyoung ones. Vivipary occurs in most mammals including human beings. It ensures proper embryonic careand protection to the embryo. The chances of survival of young ones are greater in viviparous animals thanin oviparous ones. In metatherians where the young ones are delivered without completion of proper growth,a protective and nourishing mechanism is present in the form of a marsupium.

Differences Between Ovipary and Vivipary

S. No. Ovipary Vivipary

1. The development of the embryo occurs outside The development of the embryo occurs inside the body

the body of female. of female.2. The embryo develops inside egg. The embryo develops inside uterus of the female.3. The food required for development of embryo is The food required for growth of embryo is provided

already stored in the egg. by the mother through placenta. It is not stored.4. The young one is never delivered. It hatches out The young one is delivered by the mother.

of the egg.5. Ovipary occurs in egg laying animals. Vivipary occurs in metatherians and eutherian mammals.

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$��+��+��*��In flowering plants, zygote develops into embryo. The food for development of embryo comes from a

special tissue known as endosperm. Endosperm receives food from nucellus and the plant. Ultimately, thefertilized ovule matures into a seed. A number of seeds develop in an ovary depending upon the number ofovules. Meanwhile wall of the ovary also proliferates. It produces pericarp. The pericarp can be dry orfleshy. The ripened ovary with pericarp and seeds is called fruit. As the fruit begins to develop, sepalspetals, stamens, style and stigma are shed. Sepals persist in some cases, e.g,. Pea, Withania. The fruit ismeant for protecting the young seeds. In many cases, it helps in dispersal of the mature seeds. After dispersal, theseeds which reach suitable substratum germinate and form new plants.

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�Fig 1.20. A few kinds of fruits showing seeds and protective pericarps.

1. Mention the sites where syngamy occurs in amphibians and reptiles respectively. (C.B.S.E. 2010)2. Offspring derived by asexual reproduction are called clones. Justify giving two reasons.

(C.B.S.E. 2010)3. Mention the characteristic features and a function of zoospores in some algae. (C.B.S.E. 2010)4. Name an organism where cell division is itself a mode of reproduction. (C.B.S.E. 2010)5. In Yeast and Amoeba, the parent cell divides to give rise to two new individual cells. How does the

cell division differ in these two organisms ? (C.B.S.E. 2010)

6. Name the type of cell division that takes place in the zygote of an organism exhibiting haplonticlife cycle. (C.B.S.E. 2011)

7. How does Penicillium reproduce asexually ? (C.B.S.E. 2011)

8. Name the phase all organisms have to pass through before they can reproduce sexually.

(C.B.S.E. 2011)

9. Name the group of organisms that produces non-motile male gametes. How do they reach thefemale gamete for fertilization ? (C.B.S.E. 2011)

10. Mention the unique flowering phenomenon exhibited by Strobilanthes kunthiana. (C.B.S.E. 2012)

11. Cucurbits and Papaya plants bear staminate and pistillate flowers. Mention the categories they areput separately on the basis of type of flowers they bear. (C.B.S.E. 2012)

12. Mention the unique feature with respect to flowering and fruiting in bamboo species.

(C.B.S.E. 2012)

13. Give reason : Some organisms like honeybees are called parthenogenetic animals. (C.B.S.E. 2012)

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14. Name an organism where cell division in itself is a mode of reproduction. (C.B.S.E. 2013)

15. Name an alga that reproduces asexually through zoospores. Why are these reproductive units socalled ? (C.B.S.E. 2013)

16. Name the phenomenon and one bird where the female gamete directly develops into a new organism.

(C.B.S.E. 2013)

17. Name the vegetative propagules of (a) Agave (b) Bryophyllum. (C.B.S.E. 2014)

18. Meiosis is an essential event in the sexual life cycle of an organism. Give two reasons.

(C.B.S.E. 2015)

(Hint. (i) Formation of haploid gametes. (ii) Maintenance of chromosome number and recombinations).

19. Name two animals that exhibit oestrous cycle. (C.B.S.E. 2016)

20. Name the vegetative propagules in (i) Potato and (ii) Pistia. (C.B.S.E. 2017)

21. At what state does meiosis occur in an organism exhibiting haplodiplontic life cycle and mentionthe fate of the products thus produced. (C.B.S.E. 2019)

22. Why are no variations seen in clones ? State two reasons. (C.B.S.E. 2019)

23. Why are cucurbit plants said to be monoecious ? (C.B.S.E. 2019)

24. Why are papaya plants said to be dioecious ? (C.B.S.E. 2019)

1. A moss plant produces a large number of antherozoids but relatively only a few egg cells. Why ?(C.B.S.E. 2010)

2. Why are Papaya and Date Palm plants said to be dioecious whereas cucurbits and coconut palmsare monoecious, inspite of all of them bearing unisexual flowers ? (C.B.S.E. 2008, 2010, 2014)

3. The cell division involved in gamete formation is not of the same type in different organisms.Justify. (C.B.S.E. 2011)

4. A list of three flowering plants is given below. Which ones out of them are (i) monoecious and(ii) bearing pistillate flowers.Date Palm, Cucurbits, Pea. (C.B.S.E. 2011)

5. (a) State the difference between meiocyte and gamete with respect to chromosome number.(b) Why is whiptail lizard referred to as parthenogenetic ? (C.B.S.E. 2012)

6. Why do algae and fungi shift to sexual mode of reproduction just before the onset of adverseconditions ? (C.B.S.E. 2014)

7. Why do moss plants produce very large number of male gametes ? Provide one reason. What arethese gametes called ? (C.B.S.E. 2015)(Hints. Some are able to reach archegonia, antherozoids).

8. A liverwort/moss plant is unable to complete its life cycle in a dry environment. State two reasons.(C.B.S.E. 2015)

(Hint. Water required for transport of male gametes, germination of spores and protection againstdesiccation).

9. Explain the significance of meiocytes in a diploid organism. (C.B.S.E. 2016)(Hint. Meiocytes undergo meiosis, produce haploid gametes with recombinations due to crossingover, create scope for fertilization to restore diploid condition in sexual reproduction).

10. Explain the importance of syngamy and meiosis in the sexual life cycle of an organism.(C.B.S.E. 2016)

11. (a) List the three stages, the annual and biennial angiosperms have to pass through during their lifecycle. (b) List and describe any two vegetative propagules in flowering plants. (C.B.S.E. 2017)

12. Differentiate between annual and biennial plants. Provide one example of each. (C.B.S.E. 2017)

�� 13. Mosses and frogs both need water as a medium for fertilisation. Where does syngamy occur and

how is it ensured in both these organisms ? (C.B.S.E. 2019)

14. Write the basis of categorising animals as oviparous or viviparous, giving one example of each.

(C.B.S.E. 2019)

1. Describe the various modes of asexual reproduction. 2. Write down the various natural methods of vegetative reproduction. 3. Describe the horticultural methods of vegetative propagation. 4. Describe the various phases of life cycle.5. Describe the events in sexual reproduction.

1. Why is reproduction essential for organisms ?Ans. (i) For continuity of species.

(ii) For introducing variations.(iii) For inheritance of genetic constitution.

2. Which is a better mode of reproduction, sexual or asexual ? Why ?Ans. Sexual mode because it enhances gene pool, introduces variations and number of offspring are

more.3. Why is the offspring formed by asexual reproduction referred to as clone ?

Ans. Offspring formed by asexual reproduction is morphologically and genetically identical to parent. Soit is referred as clone.

4. Offspring formed due to sexual reproduction have better chances of survival. Why ? Is thisstatement always true ?

Ans. (i) Sexual reproduction keeps the vigour and vitality of the race. It introduces genetic varia-tions, many of which are helpful to the individuals in better adaptations to the environment.

(ii) In lower organisms, sexual reproduction occurs towards the approach of unfavourableperiods. It produces a perennating zygospore. Therefore, sexual reproduction results inbetter chances of survival.However, sexual reproduction does not always lead to better chances of survival. The youngones produced through sexual reproduction are in very delicate and helpless stage so thatmost of them fall prey to predators.

5. How does the progeny formed from asexual reproduction different from those formed bysexual reproduction ?

Ans. See text.

6. Distinguish between asexual and sexual reproduction. Why is vegetative reproduction alsoconsidered as a type of asexual reproduction ?

Ans. (a) Differences Between Asexual and Sexual Reproduction. See text.

(b) Vegetative Reproduction as Type of Asexual Reproduction. Asexual reproduction is ameans of uniparental multiplication in which gametes or sex cells are not formed. Meiosisis absent and all the divisions are mitotic. The cells taking part in asexual reproduction aresomatic in nature. Vegetative reproduction is uniparental and the propagule is somatic innature. Sex cells are neither formed nor meiosis occurs. Therefore, vegetative reproduction isconsidered to be type of asexual reproduction.

7. What is vegetative propagation ? Give two suitable examples.Ans. Definition. Vegetative propagation is means of multiplication found in plants in which somatic

parts can function as propagules and form new plants.Examples. (i) Potato – pieces of tuber, each having atleast one eye.(ii) Sugarcane – basal parts of stems, each having atleast one node.

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8. Define : (i) Juvenile phase (ii) Reproductive phase (iii) Senescence phase.Ans. (i) Juvenile Phase. It is pre-reproductive phase in the life cycle of an organism which

occurs between its birth and sexual maturity and is characterised by rapid growth.(ii) Reproductive Phase. It is the phase of life cycle wherein the individuals possess the

potential to produce young ones.(iii) Senescence Phase. It is the post-reproductive phase in the life cycle that is characterised by

slowing down of metabolism, slow deterioration of function and structure of body parts.9. Higher organisms have resorted to sexual reproduction inspite of its complexity. Why ?

Ans. (i) Variations. Introduction of variations that provide competitive edge and ability to adapt.(ii) Gene Pool. Dispersal of variations and distribution of mutations in the population.(iii) Vigour and Vitality. Sexual reproduction maintains vigour and vitality of the race.(iv) Parental Care. In many cases, the young ones are protected by the parents in their

vulnerable stages.10. Explain why meiosis and gametogenesis are always interlinked ?

Ans. In sexually reproduced organisms, fertilization or fusing of two gametes forms a zygote which isdiploid in nature, i.e., it has two sets of chromosomes. The gametes are always haploid or having asingle set of chromosomes. Gamete formation or gametogenesis, therefore, involves the reductionof chromosome number from two sets to one set. It occurs through meiosis. Therefore, gametogenesisor gamete formation is linked to meiosis or reduction in chromosome number.

11. Identify each part and write whether it is haploid (n) or diploid (2n). (i) Sepal ............ (ii) branch ............ (iii) style ............ (iv) egg ............ (v) pollen ............ (vi) male gamete ............ (vii) petal ............(viii) uterus ............ (ix) ovum ............ (x) zygote ............

Ans. (i) 2n (ii) 2n (iii) 2n (iv) n (v) n (vi) n (vii) 2n (viii) 2n (ix) n (x) 2n.12. Define external fertilization. Mention its disadvantages.

Ans. Definition. External fertilization is fusion of compatible gametes outside the body of organisms,e.g., Frog.Disadvantages. (i) It occurs only in aquatic medium.(ii) A chance factor is involved requiring synchronous release of gametes nearby and absence

of turbulence of water.(iii) There is no protection to young ones. They are vulnerable to a number of predators.

13. Differentiate between a zoospore and a zygote.Ans. See text.

14. Differentiate between gametogenesis and embryogenesis.

Ans. See text.

15. Describe the post fertilization changes in a flower.

Ans. Post Fertilization Changes. Two structures are formed in a flower at the time of fertilization.They are zygote and primary endosperm cell. Zygote develops into embryo. Primary endospermcell forms a special nutritive tissue called endosperm. It provides nourishment to embryo for itsgrowth and development. Ultimately the fertilised ovule matures into seed. A number of seeds maydevelop in an ovary depending upon the number of fertilied ovules. The wall of ovary grows andproduces wall of the fruit called pericarp. Pericarp can be dry or fleshy. The ripened ovary withpericarp and seeds is called fruit. As the fruit begins to grow, sepals, petals, stamens, style andstigma are shed. Sepals persist in some cases, e.g., Pea.

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16. What is a bisexual flower ? Collect 5 bisexual flowers from your neighbourhood and with thehelp of your teacher find out their common and scientific names.

Ans. A survey to be done.

17. Examine a few flowers of any cucurbit plant and try to identify the staminate and pistillate flowers.

Ans. Observation to be done.

18. Why are offspring of oviparous animals at a greater risk as compared to offspring of viviparousanimals ?

Ans. In oviparous animals, the young ones develop inside calcareous shells outside the body of thefemale. In viviparous animals, the young ones develop inside the body of the female. They arebetter protected with ensured continued nourishment for optimum development. It is not so in caseof oviparous animals. The young ones are less efficiently protected and nourished. They are at agreater risk than the young ones of viviparous animals.

��SAMPLE PAPERSAMPLE PAPERSAMPLE PAPERSAMPLE PAPERSAMPLE PAPER—20092009200920092009

1. Why do internodal segments of Sugarcane fail to propagate vegetatively even when they are incontact with damp soil ?

Ans. A growing point or bud is required for vegetative propagation which is absent in internodal segments.

2. In Whiptail lizards only females are born generation after generation. There are no males.How is this possible ?

Ans. In Whiptail lizards (Cnemidophorus species), the young ones develop parthenogenetically from eggs.

3. In the following figure of a fruit, label the part which is protectivein function and that which is responsible for producing new plants.

Ans. See the text figure 1.19. Protective part is pericarp. New plants developfrom seeds.

SAMPLE PAPERSAMPLE PAPERSAMPLE PAPERSAMPLE PAPERSAMPLE PAPER—201020102010201020101. The Turkey usually produces females for several generations. How is this possible ?

Ans. In Turkey, the female gamete or egg can grow parthenogenetically or without fertilization directlyinto female individual.

SAMPLE PAPERSSAMPLE PAPERSSAMPLE PAPERSSAMPLE PAPERSSAMPLE PAPERS—2014-15, 2016-172014-15, 2016-172014-15, 2016-172014-15, 2016-172014-15, 2016-17

1.

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Ans. (a) Isogametes / homogametes.(b) Fertilization, zygote/zygospore.(c) Cladophora/Ulothrix/Chlamydomonas.

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��"�� Ans. (a) A layer of external water is essential for the passage of sperms to the archegonia.

(b) Formation of a large number of male gametes ensures that at least some are able to reach thefemale gametes. (c) Synchrony in the release of male and female gametes in external fertilizationensures that at least a few compatible gametes are able to meet each other and fuse.

SAMPLE PAPERSAMPLE PAPERSAMPLE PAPERSAMPLE PAPERSAMPLE PAPER—2019-202019-202019-202019-202019-201. How does an encysted Amoeba reproduce on return of favourable conditions ?

Ans. On approach of favourable conditions

(i) Encysted Amoeba first undergoes multiple fission. It produces a number of minute amoebae(= amoebules) or pseudopodiospores. The cyst wall bursts and amoebae orpseudopodiospores are released in the surrounding medium. They grow to form the matureamoebae.

(ii) In case Amoeba had formed encysted spores, each encysted spore releases a single smallamoeba directly.

2. What are gemmules and conidia ? Name an organism each in which these are formed.

Ans. Gemmules. They are perennating structures, which help in both dispersal and asexualrepoduction. Gemmules are found in sponges, e.g., Spongilla.

Conidia. Conidia are exogenously produced nonmotile spores which take part in bothdispersal and asexual reproduction. In Penicillium and Aspergillus conidia are formed in chains.

�� 1. Observe the figure of sporulation of Chlamydomonas, and answer the following questions :

(a) (i) What is sporulation ? (ii) What is its importance ?(b) Which type of nuclear division occurs during this type of sporulation ?

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(c) What type of spores are shown in the figure ? What type of habitat does it indicate ?

�� Ans. (a) (i) Sporulation. It is the formation of minute single-celled propagules or spores by a mature individual.

(ii) Sporulation is meant for dispersal and asexual reproduction.(b) Mitosis.(c) Zoospores or motile spores having flagella for locomotion in an aquatic medium. Chlamydomonas is

an aquatic organism.

1. Fill in the blanks :Plant bearing both male and female flowers is called .......... . (C.B.S.E. Main 2006)

Ans. Monoecious. 2. Fill in the blanks with appropriate examples :

Cycas, Nymphaea, Cucurbita, Candytuft, Guava, Peach, VallisneriaDioecious plants are ........ gymnosperm and ........ an angiosperm. (C.B.S.E. Main 2008)

Ans. Cycas, Vallisneria.

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1. Process of fusion of haploid cells is

(A) Cell cycle (B) Meiosis

(C) Mitosis (D) Syngamy.(H.P.P.M.T. 2001)

2. Maximum life span of Dog is

(A) 20 years (B) 15 years

(C) 10 years (D) 5 years.

(A.F.M.C. 2004)

3. Which one is vegetatively propagated by leaf

segments ?

(A) Agave and Kalanchoe

(B) Bryophyllum and Kalanchoe

(C) Asparagus and Bryophyllum

(D) Chrysanthemum and Agave.

(C.B.S.E. 2005)

4. Scion is grafted on stock. Quality of fruitsproducted will depend upon genotype of

(A) Scion (B) Stock

(C) Both A and B (D) None of the above.

(A.I.I.M.S. 2006)

5. Which one undergoes longitudinal binary fission ?

(A) Euglena (B) Plasmodium

(C) Planaria (D) Paramoecium.

(Kerala 2007)

6. Fusion of male gamete with a female gametes

is

(A) Syngamy (B) Porogamy

(C) Double fertilization

(D) Triple fusion. (Manipur 2007)

7. Sweet Potato multiples vegetatively through

(A) Leaves (B) Parthenogenesis

(C) Roots (D) Buds.

(M.H.C.E.T. 2008)

8. Plants with poor root system are propagatedthrough

(A) Layering (B) Leaf cuttings

(C) Stem cuttings (D) Grafting.

(M.H.C.E.T. 2008)

9. How is diploid offspring produced throughparthenogenesis

(A) From haploid egg cell without fertilization

(B) From diploid egg cell without fertilization

(C) From fertilization of haploid egg cell

(D) From fertilization of diploid egg cell.

(Guj. C.E.T. 2008)

10. Vegetative propagation occurs in Mint through

(A) Runners (B) Suckers

(C) Offsets (D) Rhizome.

(C.B.S.E. 2009)

11. The term parthenogenesis was coined by :

(A) Boveri (B) Balfour

(C) Grobber (D) Owen. (C.E.T. Chd. 2010)

�� 12. In grafting, stock is

(A) Stem of desired variety

(B) Bud of desired variety

(C) Part of rooted plant

(D) Part to be grafted. (M.H.C.E.T. 2010)

13. If stock contains 58 chromosomes and scioncontains 30 chromosomes, then how manychromosomes are present in root and egg cellof resultant plant respectively.

(A) 30 and 29 (B) 15 and 58

(C) 58 and 15 (D) 29 and 30.

(Guj. C.E.T. 2011)

14. Asexual reproductive structure of Hydra is

(A) Gemmule (B) Bud

(C) Conidia (D) None of the above(H.P.P.M.T. 2011)

15. Which one is common to multicellular fungi,filamentous algae and moss protonema

(A) Mode of nutrition

(B) Diplontic life cycle

(C) Members of kingdom plantae

(D) Multiplication by fragmentation.

(C.B.S.E. 2012)

16. Find out correct order of vegetative propagulesof plants like Potato, Ginger, Agave,Bryophyllum and Water Hyacinth

(A) Offset, bulbil, leaf bud, rhizome and eyes

(B) Leaf bud, bulbil, offset, rhizome and eyes

(C) Eyes, rhizome, bulbil, leaf bud and offset

(D) Rhizome, bulbil, leaf bud, eyes and offset

(E) Offset, bulbil, leaf bud, rhizome and eyes.(Kerala 2012)

17. Meiosis takes place in

(A) Megaspore (B) Meiocyte

(C) Conidia (D) Gemmule.(N.E.E.T. 2013)

18. In Water Hyacinth, vegetative propagationoccurs by

(A) Offset (B) Rhizome

(C) Leaf bud (D) Bulbil.

(A.M.U. 2013)

19. Chromosome number of Apple meiocytes is

(A) 46 (B) 34

(C) 78 (D) 12.

(J.K.C.E.T. 2014)

20. Which one shows isogamy with nonflagellatedgametes.

(A) Ulothrix (B) Ectocarpus

(C) Spirogyra (D) Sargassum.

(C.B.S.E. 2014)

21. Stock and scion are used in

(A) Cutting (B) Grafting

(C) Layering (D) Micropropagation.

(W.B. 2015)

22. Flowers are unisexual in

(A) Pea (B) Cucumber

(C) China Rose (D) Onion.

(C.B.S.E. 2015)

23. Asexual reproduction through formation ofgemmule occurs in

(A) Ascidia (B) Hydra

(C) Planaria (D) Spongilla.

(M.H.C.E.T. 2016)

24. Which one of the following generates newgenetic combination leading to variation

(A) Nucellar polyembryony

(B) Vegetative reproduction

(C) Parthenogenesis

(D) Sexual reproduction. (N.E.E.T.-II 2016)

25. Which is used to maintain genetic traits of agreen plant

(A) Treating seeds with gamma radiations

(B) Building hybrids through intergenericpollination

(C) Propagation through vegetative multipli-cation

(D) Propagation through seed germination. (A.I.I.M.S. 2017)

26. Which of the following flowers only once inthe life time

(A) Mango (B) Jackfruit

(C) Bamboo species (D) Papaya.

(N.E.E.T. 2018)

27. Offsets are produced by

(A) Parthenocarpy (B) Mitotic divisions

(C) Meiotic divisions (D) Parthenogenesis.

(N.E.E.T. 2018)

28. In some plants, the female gamete developsinto embryo without fertilisation. Thephenomenon is known as

(A) Autogamy (B) Parthenocarpy

(C) Syngamy (D) Parthenogenesis.

(N.E.E.T. 2019)

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1. (D) 2. (A) 3. (B) 4. (A) 5. (A) 6. (A) 7. (C) 8. (D) 9. (B) 10. (B)11. (D) 12. (C) 13. (C) 14. (B) 15. (D) 16. (C) 17. (B) 18. (A) 19. (B) 20. (C)21. (B) 22. (B) 23. (D) 24. (D) 25. (C) 26. (C) 27. (B) 28. (D)

1. A few statements describing certain featuresof reproduction are given below :(i) Gametic fusion takes place.(ii) Transfer of genetic material takes place.(iii) Reduction division takes place.(iv) Progeny have some resemblances with

parents.Select the options that are true for both asexualand sexual reproduction from the options givenbelow :(A) (i) and (ii) (B) (ii) and (iii)(C) (ii) and (iv) (D) (i) and (iii).

2. The term clone cannot be applied to offspringformed by sexual reproduction because :(A) Offspring do not possess exact copies of

parental DNA.(B) DNA of only one parent is copied and

passed on to the offspring.(C) Offspring are formed at different times.(D) DNA of parent and offspring are com-

pletely different.3. Amoeba and Yeast reproduce asexually by fis-

sion and budding respectively because theyare :(A) Microscopic organisms(B) Heterotrophic organisms

(C) Unicellular organisms

(D) Uninucleate organisms.

4. A few statements with regard to sexual repro-duction are given below

(i) Sexual reproduction does not always re-quire two individuals.

(ii) Sexual reproduction generally involves ga-metic fusion

(iii) Meiosis never occurs during sexual repro-duction.

(iv) External fertilization is a rule duringsexual reproduction.Choose the correct statements from the op-tions below :

(A) (i) and (iv) (B) (i) and (ii)(C) (ii) and (iii) (D) (i) and (iv).

�� 5. A multicellular filamentous alga exhibits a type

of sexual life cycle in which the meioticdivision occurs after the formation of zygote.The adult filament of this alga has :(A) Haploid vegetative cells and diploid ga-

metangia(B) Diploid vegetative cells and diploid ga-

metangia

(C) Diploid vegetative cells and haploidgametangia

(D) Haploid vegetative cells and haploidgametangia.

6. The male gametes of rice plant have 12chromosomes in their nucleus. The chromosomenumber in the female gamete, zygote and thecells of the seedling will be respectively.(A) 12, 24, 12 (B) 24, 12, 12(C) 12, 24, 24 (D) 24, 12, 24.

7. Given below are a few statements related toexternal fertilization. Choose the correct state-ments

(i) The male and female gametes are formedand released simultaneously.

(ii) Only a few gametes are released into themedium

(iii) Water is the medium in a majority of or-ganisms exhibiting external fertilization.

(iv) Offspring formed as a result of externalfertilization have better chance of survivalthan those formed inside an organism

(A) (iii) and (iv) (B) (i) and (iii)(C) (ii) and (iv) (D) (i) and (iv).

8. The statements given below describe certainfeatures that are observed in the pistils of flow-ers(i) Pistil may have many carpels(ii) Each carpel may have more than one

ovule(iii) Each carpel has only one ovule(iv) Pistil has only one carpel. Choose the

statements that are true from the optionsbelow

�, �� (A) (i) and (ii) (B) (i) and (iii)(C) (ii) and (iv) (D) (iii) and (iv).

9. Which of the following situations correctly de-scribe the similarity between an anogiospermegg and a human egg ?(i) Eggs of both are formed only once in a

lifetime(ii) Both the angiosperm egg and human egg

are stationary(iii) Both the angiosperm egg and human egg

are motile and transported(iv) Syngamy in both results in the formation

of zygoteChoose the correct answer from the optionsgiven below(A) (ii) and (iv) (B) (iv) only(C) (iii) and (iv) (D) (i) and (iv).

10. Appearance of vegetative propagules from thenodes of plants such as Sugarcane and Gingeris mainly because(A) Nodes are shorter than internodes(B) Nodes have meristematic cells(C) Nodes are located near the soil(D) Nodes have non-photosynthetic cells.

11. Which of the following statements, support theview that elaborate sexual reproductive processappeared much later in the organic evolution(i) Lower groups of organisms have simpler

body design(ii) Asexual reproduction is common in lower

groups of organisms(iii) Asexual reproduction is common in higher

groups of organisms(iv) The high incidence of sexual reproduction

in angiosperms and vertebrates. Choose thecorrect answer from the options givenbelow :

(A) (i) and (iii) (B) (i) and (ii)(C) (ii) and (iv) (D) (ii) and (iii).

12. Offspring formed by sexual reproduction exhibitmore variation than those formed by asexualreproduction because(A) Sexual reproduction is a lengthy process.(B) Gametes of parents have qualitatively dif-

ferent genetic composition.(C) Gametic material comes from parents of

two different species.(D) Greater amount of DNA is involved in

sexual reproduction.

13. Choose the correct statement from amongst thefollowing(A) Dioecious organisms are seen only in

animals(B) Dioecious organisms are seen only in plants(C) Dioecious organisms are seen in both plants

and animals(D) Dioecious organisms are seen only in

vertebrates.14. There is no natural death in single celled

organisms like Amoeba and bacteria because(A) They cannot reproduce sexually(B) They reproduce by binary fission(C) Parental body is distributed amongst the

daughters(D) They are microscopic.

15. There are various types of reproduction. Thetype of reproduction adopted by an organismdepends upon(A) The habitat and morphology of the

organism(B) Morphology of the organism(C) Morphology and physiology of the

organism(D) The organism’s habitat, physiology and

genetic makeup.16. Identify the incorrect statement

(A) In asexual reproduction, the offspring pro-duced are morphologically and geneticallyidentical to the parent

(B) Zoospores are sexual reproductive struc-tures

(C) In asexual reproduction, a single parentproduces offspring with or without the for-mation of gametes.

(D) Conidia are asexual structures inPenicillium.

17. Which of the following is a post-fertilizationevent in flowing plants ?(A) Transfer of pollen grains(B) Embryo development(C) Formation of flower(D) Formation of pollen grains.

18. The number of chromosomes in the shoot tipcells of Maize plant is 20. The number of chro-mosomes in the microspore mother cells of thesame plant shall be(A) 20 (B) 10

(C) 40 (D) 15.

1. (C) 2. (A) 3. (C) 4. (B) 5. (D) 6. (C) 7. (B) 8. (A) 9. (B) 10. (B)11. (C) 12. (B) 13. (C) 14. (C) 15. (D) 16. (B) 17. (B) 18. (A).

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1. Mention two inherent characteristics of Amoeba and Yeast that enable them to reproduceasexually.

Ans. (i) Unicellular nature. (ii) Simple body structure.

2. Why do we refer to offspring formed by asexual method of reproduction as clones ?

Ans. They resemble both morphologically and genetically to one another as well as their parents.

3. Although potato tuber is an underground part, it is considered as stem. Give two reasons.

Ans. (i) Presence of nodes and internodes.

(ii) Formation of plantlets from buds present over the nodes.

4. Between an annual and a perennial plant, which one has a shorter juvenile phase ? Give onereason.

Ans. Annual plant has a shorter juvenile phase as it has to complete its life cycle within one season.

5. Rearrange the following events of sexual reproduction in the sequence in which they occur ina flowering plant :

embryogenesis, fertilisation, gametogenesis, pollination.

Ans. Gametogenesis, pollination, fertilisation and embryogenesis.

6. The probability of fruit set in a self-pollinated bisexual flower of a plant is far greater than adioecious plant. Explain.

Ans. In self pollinated bisexual flower fertilization and hence fruit set is ensured. This is not so in dioe-cious cross pollinated plants where 50% of the plants are male and hence unable to bear fruits.

7. Is the presence of large number of chromsomes in an organism a hindrance to sexual reproduction ?Justify your answer by giving suitable reasons.

Ans. Yes. Large number of chromosomes are very difficult to get accomodated in paired state over theequator in metaphase I. Crossing over and disjunction are also disturbed resulting in unequal distri-bution of chromosomes and non-functioning of gametes.

8. Is there a relationship between the size of an organism and its life span ? Give two examplesin support of your answer.

Ans. Life span is not related to size of the organisms. Crow and parrot are of equal size. Crow has lifespan of only 15 years while parrot lives for 140 years. Mango and peepal trees are similarly ofnearly equal size with mango living for 200 years and peepal living for 2500 years.

9. Give reasons as to why cell division cannot be a type of reproduction in multicellular organ-isms.

Ans. Cell division adds new cells to the body of a multicellular organism but does not divide the sameso that it is not a method of reproduction (as in case of unicellular organisms).

10. In the given figure, mark the ovule and pericarp.

Ans. See Fig. 1.19 (Pea)

11. Why are gametes produced in large number in organisms that exhibit external fertilization ?

Ans. External fertilization occurs in aquatic habitat where male and female individuals pass out theirgametes in large number so that at least a few compatible gametes come in contact and fuse inpairs.

12. Which of the following are monoecious and dioecious organsims ?

(a) Earthworm ________________ (b) Chara ________________

(c) Marchantia ________________ (d) Cockroach ________________

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Ans. (a) Monoecious (b) Monoecious (c) Dioecious (d) Dioecious.

13. Match the organisms given in column A with the vegetative propagules given in column B

Column A Column B

(i) Bryophyllum (a) Offset

(ii) Agave (b) Eyes

(iii) Potato (c) Leaf buds

(iv) Water Hyacinth (d) Bulbils.

Ans. (i)—(c), (ii)—(d), (iii)—(b), (iv)—offset.

14. What do the following parts of a flower develop into after fertilisation ?

(a) Ovary _____ (b) Ovules ______.

Ans. (a) Fruit

(b) Seeds.

1. In haploid organisms that undergo sexual reproduction, name the stage in the life cycle when

meiosis occurs. Give reasons for your answers.

Ans. Stage of Meiosis. Germination of zygote (zygotic meiosis).

Reason. Haploid nature of organisms.

2. The number of taxa exhibiting asexual reproduction is drastically reduced in higher plants

(angiosperms) and higher animals (vertebrates) as compared to lower groups of plants and ani-

mals. Analyse the possible reasons for this situation.

Ans. Asexual reproduction does not produce variations. Sexual reproduction produces a lot of variations

due to random separation of homologous chromosomes, crossing over and chance recombination.

Angiosperms and vertebrates have complex structural organisation and longer life span. They have

adopted sexual reproduction for increased adaptability and high competitiveness.

3. Honeybees produce their young ones only by sexual reproducton. Inspite of this, in a colony of

bees we find both haploid and diploid individuals. Name the haploid and diploid individuals in

the colony and analyse the reasons behind their formation.

Ans. Honey bees have three types of individuals in their colony : (i) Sterile diploid females as workers.

(ii) One fertile diploid female as queen and (iii) Fertile haploid males as drones. Haploid drones

develop from unfertilised eggs. Queen and workers develop from fertilised eggs. The difference

between the two is diet which makes the queen fertile while workers remain sterile.4. With which type of reproduction do we associate the reduction division ? Analyse the reasons

for it.Ans. Meiosis or reduction division is associated with sexual reproduction due to following reasons :

(i) Gametes, which fuse in pairs during sexual reproduction, must be haploid.(ii) Germ cells which produce gametes are diploid. Only meiosis or reduction division can bring

down the chromosome number to haploid state.

(iii) Reduction division maintains the chromosome number generation after generation.

5. Is it possible to consider vegetative propagation observed in certain plants like Bryophyllum,Water Hyacinth, Ginger, etc as a type of asexual reproduction ? Give two/three reasons.

Ans. Vegetative reproduction is asexual reproduction because

(i) It is uniparental. (ii) Unit of reproduction is a propagule formed from somatic cells of the parent.(iii) There is no meiosis nor formation of gametes. (iv) The progeny is clone of the parent.

6. ‘Fertilization is not an obligatory event for fruit formation in certain plants ! Explain the state-ment.

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Ans. Fertilization is not obligatory in parthenocarpic fruits which are seedless in nature. Partheno-carpy is natural in Banana, seedless grapes and seedless oranges. In others it is induced by sprayinggrowth hormone over their flowers. The ovules of such fruits do not develop into seeds.

7. In developing embryo, analyse the consequences if cell divisions are not followed by cell dif-ferentiation.

Ans. Cell Divisions Not followed by Cell Differentiation. Only a cellular mass will be produced wherethere is no differentiation of embryo axis, plumule, radicle and cotyledons (in case of floweringplants) or other organs. A new individual cannot develop from such an embryo.

8. List the changes observed in an angiosperm flower subsequent to pollination and fertilization.

Ans. (i) Zygote develops into embryo. (ii) Primary endosperm cell gives rise to endosperm.(iii) Integuments develop into seed coats. (iv) Ovary grows to form a fruit having one or moreseeds. (v) Some floral parts may fuse with fruit but mostly they wither and fall down (calyx, corolla,

stamens, style, stigma).

9. Suggest a possible explanation why seeds in a pea pod are arranged in a row whereas those intomato are scattered in the juicy pulp.

Ans. Number, type and growth of placentae determine the arrangement of seeds in the fruit. In Pea,there is marginal placentation. The placenta does not grow during fruit formation so that the seedsremain distinct and free. In tomato, the placentation is axile. The placentae grow and form a pulpymass that fills the fruit interior. Therefore, the seeds are scattered and embedded in a juicy pulp.

10. Draw the sketches of a zoospore and a conidium. Mention two dissimilarities between themand at least one feature common to both structures.

Ans. (a) Draw Figure 1.6.

(b) Common Feature. Both take part in dispersal and asexual reproduction.

(c) Dissimilarities

Zoospore Conidium

1. It is a flagellate spore. 1. It is a non-flagellate spore.

2. The spore develops endogenously 2. The spore develops exogenously at the tip

inside a sporangium. of conidiophore branch called sterigma.

11. Justify the statement ‘vegetative reproduction is also a type of asexual reproduction.’

Ans. See SAQ 5 above.

12. Vivipary automatically limits the number of offspring in a litter. How ?

Ans. In vivipary, the embryos develop into young ones inside the womb or uterus of the mother. There islimitation of space and nourishment that the mother can provide. Therefore, the number of off-spring become limited from one to a few only.

1. Enumerate the differences between asexual and sexual reproduction. Describe the type of the

asexual reproduction exhibited by unicellular organisms.

Ans. (a) Differences between Asexual and Sexual Reproduction. See text.

(b) Asexual Reproduction in Unicellular Organisms.

(i) Binary Fission. See text.

(ii) Multiple Fission. See text.

(iii) Torulation or Budding. See text.

(iv) Sporulation (e.g., Chlamydomonas). See text

2. Do all the gametes formed from a parent organism have the same genetic composition (identi-cal DNA copies of the parental genome) ? Analyse the situation with the background of game-togenesis and provide or give suitable explanation.

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Ans. (i) No. (ii) Gametes do not have the same genetic composition. A lot of variations develop in them.The two main factors are

(a) Recombinations due to crossing over during pachytene-diplotene stage of meiosis I. Here non-sister chromatids exchange segments. This results in several new combinations of DNA sequences.

(b) Change separation of homologous chromosomes at anaphase I.

(c) Chance distribution of recombined chromosomes during formation of gametes.

3. Although sexual reproduction is a long drawn, energy-intensive complex form of reproduction,many groups of organisms in kingdoms Animalia and Plantae prefer this mode of reproduc-tion. Give at least three reasons for this.

Ans. It is because sexual reproduction is highly beneficial.

1. It pools the genetic resources of two different individuals that gives a sort of hybrid vigour.

2. Genetic recombinations occur during gametogenesis due to (a) crossing over (b) chance separationof homologous chromosomes dusting meiosis-I. (c) Chance separation of recombined chromosomesduring meiosis-II

3. Sexually reproduced individuals have a lot of variations which give them a better chance ofsurvival in changing environment and better fitness in the struggle for existence.

4. Differentiate between (a) Oestrus and menstrual cycles (b) Ovipary and vivipary. Cite an ex-ample for each type.

Ans. (a) Oestrus and Menstrual Cycles. See text.

(b) Ovipary and Vivipary. See text.

5. Rose plants produce large, attractive bisexual flowers but they seldom produce fruits. On theother hand a tomato plant produces plenty of fruits but they have small flowers. Analyse thereasons for failure of fruit formation in Rose.

Ans. Both Rose and Tomato are domesticated plants which have been artificially selected by humans fordifferent purposes : (i) Rose for colourful and scented flowers and (ii) Tomato for larger pulpyfruits.

The reasons for failure of fruit formation in Rose are (a) Most of the Rose varieties are hybrids.(b) They are vegetatively propagated for quicker multiplication and growth. (c) With continuedselection and vegetative propagation, the sexual apparatus has degenerated. The failure of Rose toform fruits can be due to

1. Self incompatibility.

2. Non-viability of pollen grains.

3. Abortive ovules.

4. Non-functional egg.

5. Abnormal meiosis.

6. Inability of pollen tubes to grow and reach the ovules.

�� Flower has myriads of forms, scents, perfumes, nectar and colours. Since times immemorial, flower

has been object of admiration, aesthetic, ornamental, social, religious and cultural value. It has been usedas a symbol of conveying human feelings of love, affection, happiness, grief and mourning. For angiosperms,flower is the site of sexual reproduction. All the diversity of structure, colour, scent, nectar, etc. offlowers, are devices to ensure sexual reproduction, form seeds and fruits. Sexual reproduction is theprocess of formation and fusion of haploid gametes resulting in the production of a diploid zygote that growsto produce a new individual or offspring. Flower has two types of sex organs, male stamens and femalecarpels or pistils. They are exposed after anthesis or opening of floral bud. Meiosis occurs resulting information of microspores or pollen grains in anther part of stamens and megaspores in ovule part of carpels.The phenomenon is called sporogenesis. Pollen grain produces male gametophyte having two male gametes.Megaspore produces female gametophyte or embryo sac having one female gamete or oosphere. Colour, scentand nectar are devices to attract insects and other animals for transferring pollen grains from anthers to thereceptive part of carpels or pistils.

�� Camerarius (1694). First to study sexual reproduction in plants. He found that Mulberry,

Mercurialis, Ricinus and Zea have two types of plants, male and female. The female plantscould bear fruits only if male plants occurred nearby. He also distinguished stamens to bemale reproductive organs and carpels to be female organs.

� Amici (1824). Discovered pollen tube in Portulaca.� Strasburger (1884). Observed fusion of male and female gametes in Monotropa and other

plants.� Nawaschin (1898). Discovered double fertilization and triple fusion in Fritillaria and Lilium.� Anthesis. Opening of floral bud to form flower.� Floriculture. Growing of ornamental flowers.� Horticulture. The art of cultivation and management of gardens.� Eusporangiate. Development of sporangium with multi-layered wall from several initial

cells.� Leptosporangiate. Development of a stalked sporangium from a single initial cell.

�� A number of hormonal, meristematic, embryological and structural transformations occur prior to

initiation of flowering. Shoot apical meristem is transformed into reproductive meristem. It grows to forminflorescence axis over which floral primordia develop. They grow into floral buds and then flowers. In theflowers differentiate androecium or whorl of stamens and gynoecium or carpels (= pistils).�� !"#$%#"��& '��(��#))��"� �

Male reproductive organs of a flower are stamens. They are collectively called androecium. Thenumber, length and form of stamens are varied and specific for various types of flowers. Each stamen hastwo parts, filament and anther.

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� Fig. 2.1. L.S. flower.

1. Filament. It is sterile, long thread like structure or stalk. At its proximal end, it is attached tothalamus or petals (in epipetalous forms).

2. Anther. It is knob like, terminal, fertile and generally bilobed part of a stamen which is attachedvariously at the tip of filament.

�� The broader terminal fertile part of the stamen is

called anther. It has two parallel, similar, nearly cylindricalparts called anther lobes. The two anther lobes areseparated in front by a deep groove. They are attached toeach other on the back by a band of vasculated steriletissue called connective. Elongation of connective tissuemakes the anther lobes divergent. In family Malvaceae(Cotton, Shoe Flower) anthers are single lobed. Singlelobed anthers are c alled monothecous while two-lobedanthers are known as bithecous or dithecous*.

Each anther lobe has two long parallel cylindricalmicrosporangia. Haploid microspores are formed in themthrough the process of microsporogenesis. Microsporangiaare then transformed into pollen sacs or pollen chambers.However, the terms microsporangia and pollen sacs areused interchangeably. As each anther lobe has twomicrosporangia, the whole anther comes to have fourmicrosporangia. It is, therefore, tetrasporangiate. Theymake the anther four sided or tetragonal with onemicrosporangium being present at each corner. The twomicrosporangia or pollen sacs of an anther lobe are separatedinternally by a strip of sterile tissue. They are distinguishedexternally by a shallow groove. The whole anther is coveredexternally by a common epidermis. Pollen sacs or

*NCERT mentions that each anther lobe has two theca (thecae, thecas) and is, therefore, dithecous.

�Fig. 2.2. A, parts of a stamen. B, three dimensional cut section of an anther.

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��/'�)��%"#('!� #�� )#0�" �&��)��$ *1microsporangia develop hypodermally as four strips of archesporium, one at each corner of anther. Such adevelopment is called eusporangiate. Cells of archesporium divide periclinically into parietal cells on the outerside and sporogenous cells on the inner side. The outer parietal cells divide two to three times to formmicrosporangial wall.

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�Fig. 2.3. A, stamen. B, section of a young tetrasporangiate anther.

�� Microsporangium is cylindrical structure that runs on either side of each anther lobe. It appears circular

in transverse section. Microsporangium consists of two parts, microsporangial wall and sporogenous tissue.

1. Microsporangial Wall. Including the common epidermis of anther, each microsporangium has fourtypes of wall layers – epidermis, endothecium, middle layers and tapetum. The outer three layers are mainlyprotective in nature while the fourth layer of tapetum provides nourishment to sporogenous tissue.

(i) Epidermis. It is a common covering layer of the anther. The cells are small and thin walled. In themature anther, the epidermal cells get stretched and shrivel.

(ii) Endothecium. It is the hypodermal wall layer of microsporangium or pollen sac. The cells are large-sized. They often develop fibrous thickenings of cellulose on inner and radial walls. The mature cells becomedead. Endothecium is also called fibrous layer due to presence of fibrous thickenings. In such anthers, thehypodermal (as well as epidermal) cells present in the region of shallow groove between the microsporangia ofan anther lobe remain thin-walled to function as stomium or line of dehiscence.

(iii) Middle Layers. They are 1-3 layers of thin-walled cells present in the wall of each microsporangiumbelow the layer of endothecium. The cells of middle layers are ephemeral. However, they may containstarch grains and even develop some fibrous thickenings.

(iv) Tapetum. It is the inner specialised nourishing layer of microsporangial wall. The cells have densecytoplasm. They become large, multinucleate and polyploid through endomitosis and endopolyploidy. Tapetumis of two types.

(a) Amoeboid (Invasive). Tapetal cells grow and fuse to form a periplasmodium that passes in between the sporemother cells, for providing them nourishment and other materials, e.g., Alisma, Typha, Tradescantia, Lily.

(b) Secretory or Glandular. Tapetal cells remain in situ in parietal position. They secrete nourishmentthat passes into sporogenous cells, e.g., Symphoricarpus. Ultimately both types of tapetum will degenerate.

Functions of Tapetum. (i) It provides nourishment to growing sporogenous cells, microspore mothercells as well as young microspores. (ii) Tapetum provides enzyme callase (Mepham and Lane, 1969) fordissolution of callose binding the microspores. (iii) It secretes hormones (e.g., IAA) that are stored in pollengrains for their early growth. (iv) Tapetum secretes Ubisch granules which provide most of thesporopollenin and other materials for exine part of pollen grain covering (early part of exine is formed bymicrospores themselves). (v) It provides pollenkitt covering around the entomophilous pollen grains. (vi)Tapetum provides compatibility-incompatibility proteins to pollen grains.

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�Fig. 2.4. Development of Pollen Sacs. A, anther primordium, B, differentiation of archesporium. C,first division of archesporium. D, differentiation of parietal and sporogenous cells. E, partof anther with pollen sac.

2. Sporogenous Tissue. It fillsthe interior of microsporangium. Allthe cells are similar and calledsporogenous cells. Sporogenous cellsdivide regularly to form diploidmicrospore mother cells or pollengrain mother cells (MMC or PMC).They are initially connected byplasmodesmata. Plasmodesmata arebroken by formation of callose layersinner to cell wall. Microsporemother cells separate.

Microsporogenesis. The separated mother cells round off and undergo meiosis to form four haploidmicrospores. This phenomenon of formation of haploid microspores from a microspore or pollen mother cellthrough meiosis is known as microsporogenesis (Fig. 2.5). Microspores grow and differentiate into pollengrains. Several thousands microspores or pollen grains develop in each microsporangium. The arrangementsof 4 pollen grains in the pollen grain tetrad (Fig. 2.6) can be tetrahedral (dicots), isobilateral (monocots),linear, T–shaped and decussate.

As the anthers mature and dehydrate, the wall of the microspore mother cell degenerates. Themicrospores separate and develop into pollen grains. However, in some cases they do not separate but

remain united in tetrads called compound pollengrains, e.g., Cryptostegia, Juncus, Typha. InOrchids and Milkweeds (Asclepias, Calotropis)all the pollen grains of an anther lobe remainunited in a sac called pollinium.

�Fig. 2.6. Different types of Microspore Tetrads.

�Fig. 2.5. Microsporogenesis.

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�Fig. 2.7. A, microspore tetrad. B, growth of a microspore into a pollen grain.

In Milkweeds, 2 adjacent pollinia are connected to a sticky centre or corpusculum by means of a

small stalks called caudicles. The whole structure is known as translator. It is transferred to stigma by

insects.

�Fig. 2.8. T.S. mature anther at the time of dehiscence.

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Dehiscence. Mature anther dries up. The sterile tissue between the two pollen sacs of each anther lobedisintegrates to form a single cavity having a large number of pollen. The mature anther comes to have twopollen filled cavities, one in each anther lobe. The covering of each cavity now consists of only endotheciumand epidermis. The dead endothecial cells contract in the region of their outer thin walls and become nearlyconcave. Endothecium shortens and ruptures the thin-walled cells of stomium. It produces two longitudinal slits,one in each anther lobe. The slits expose the pollen grains for pollination. In some cases, endothecium does notbecome fibrous. Here dehiscence occurs by local degeneration of wall to form apical slits, valves, etc.

��It represents the male reproductive propagule or young male gametophyte which is formed inside the

anther and is meant for reaching the female reproductive organ through a pollinating agency. Pollen grain isgenerally rounded in outline but can be oval or pyramidal. The size varies from 25—50 �m. The colour islight yellow but other colours also occur. The surface designs vary from species to species. Pollen grains orpollens can be easily observed as yellow powdery mass when you touch the ripe anthers of Hibiscus or otherplant. They can be sprinkled over a drop of dilute glycerine and observed under the microscope.

When first formed, the pollen grain is unicellular with dense uninuclear cytoplasm. Later on, pollengrain becomes 2-3 celled. In 60% of the cases, the mature pollen grains contain 2 cells, a large vegetativeor tube cell and a small spindle shaped generative cell. In remaining cases, the generative cell dividesfurther to form two male gametes. Generative cell or male gametes float in the cytoplasm of vegetativecell. Vegetative cell has its own plasma membrane. During development the cytoplasm of vegetative ortube cell becomes vacuolate. It comes to have good amount of starch and unsaturated oils. The unsaturatedoils are believed to protect the pollen grains from radiation damage. The pollen grain is covered by a2-layered wall called sporoderm. The two layers of sporoderm are inner intine and outer exine(Fritsch, 1837).

1. Intine. It is inner layer of pollen grain wall which is made of cellulose and pectin. Some enzymaticproteins also occur in the intine (Knox and Heslop-Harrison, 1971). Intine is normally thin. However, inmembers of Lauraceae and Scitamineae (Erdtman, 1971 ; Stone et al, 1980), intine is quite thick (exine iscorrespondingly thin).

2. Exine. It is the outer layer of pollen grain wall which is made of a highly resistant biochemicalcalled sporopollenin (Zelisch, 1932). Sporopollenin is related to cutin and suberin. It is formed by oxidativepolymerisation of carotenoids. Sporopollenin is one of the most resistant organic substances. It is notaffected by high temperature, strong acid or alkali. No enzyme is known to degrade it. Because of thepresence of sporopollenin, pollen grains of the past plants are well preserved as microfossils.

Exine surface may be smooth, pitted, reticulate, spiny, warty, etc. Exine sculpturing are specific foreach type of pollen grain. Exine and hence sporopollenin is absent over certain specific regions called germpores (rounded and oval areas) or germinal furrows (elongated areas). On the basis of number of germpores or germinal furrows, pollen grains are called monocolpate, bicolpate, tricolpate, multicolpate, etc. Inmonocots, the pollen grains are generally monocolpate with a single germinal furrow. In dicots, pollengrains are commonly tricolpate with three germ pores. The study of characteristics of pollen grains, sporesand other similar structures is called palynology.

Smooth pollen occur in anemophilous plants. In entomophilous pollen grains, exine is spiny as well ascovered by a yellowish sticky fatty substance known as pollenkitt (tryphine in brassicaceae). It helps inadhering to the body of insect pollinator as well as to the stigma. Other substances associated with exine areproteins for enzymatic and compatibility-incompatibility reactions. Exine is made of two layers, outerektexine and inner endexine.

(i) Ektexine. It is outer part of exine which is further differentiated into three layers—foot layer,baculate layer and tectum.

Foot Layer. It is innermost continuous layer of ektexine over which sculptured part is attached.

��/'�)��%"#('!� #�� )#0�" �&��)��$ *5Baculate Layer. It is middle layer of ektexine which is made of rod-like elements called bacula or

columellae.Tectum. Tectum is the outer layer of ektexine which forms a sort of roof over the baculate layer. It

can be smooth or variously sculptured. Both baculate layer and tectum produce design over the surface ofpollen grains. The designs help the palynologists to identify the pollen grains as to its class, family, genusand species.

(ii) Endexine. It is inner smooth layer of exine which is differentiable from foot layer of ektexine onthe outer side and cellulose rich intine on the inner side.

Some workers differentiate exine into sexine and nexine. Sexine has two sublayers of tectum andbaculate layer while nexine has two sublayers of foot layer and endexine.

�� 1. Pollen Food Supplements. Pollen grains possess abundant nutrients including proteins, carbohydrates

and unsaturated fats. They are being used as food supplements in the form of tablets and syrups in westerncountries for enhancing vital body functions. Pollen consumption is believed to increase performance of racehorses and athletes.

2. Pollen Creams. Pollen grains possess unsaturated fats which protect the pollen grains from ultravioletrays. Because of them the grains are used in creams, emulsions and other cosmetics for providingsmoothness and protection to skin.

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�� !The period for which pollen grains remain functional is called pollen viability. It depends upon

prevailing temperature, humidity and genetic potentiality. Pollen grains of some cereals (e.g. Wheat, Rice)remain viable for only 30 minutes. Self pollination occurs in many such cases. Pollen grains of members ofRosaceae, Fabaceae (Leguminosae) and Solanaceae remain viable for several months. Pollen grains canalso be cryopreserved in liquid nitrogen (temperature –196°C) and used as pollen bank, similar to seedbank in crop breeding.

�� !Pollen grains of some plants produce severe allergy and bronchial afflictions leading to chronic

respiratory disorders. Since pollens are released in particular seasons, pollen allergy is seasonal in nature.It is also called hay fever. The common respiratory disorders are asthma, bronchitis and rhinitis. Carrotgrass (Parthenium hysterophorus) that came in India alongwith imported wheat has spread all over thecountry. It is now a major source of pollen allergy besides harming internal body organs. Some othercommon plants causing pollen allergy are Amaranthus, Chenopodium, Sorghum, Prosopis, Castor, Grass,etc.

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� Palynology. Study of pollen grain characteristics or pollen grain analysis and pollen distribution.

� Geopalynology. Study of fossilised pollen grains and spores.

� Latropalynology. Pollen grains and spores in criminology and medicines.

� Melitopalynology. Pollen grains in honey and its products.

� Mellivorous. Feeding on honey.

�� !��Development of male gametophyte is precocious, that is, it begins before the pollen grain is shed from

pollen sac. At the time of shedding for pollination, pollen grain is already an immature male gametophyte.Development of pollen grain occurs in two steps, prepollination development and post-pollination development.

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�Fig. 2.10. Pollen grain. A, external appearance of tricolpate pollen grain with spiny outgrowths.B, external appearance of a monocolpate pollen grain with surface reticulations.

C, internal structure of a mature pollen grain.

1. Pre-Pollination Development. In the newly differentiated pollen grain, nucleus is central andcytoplasm dense. Cytoplasm is surrounded by plasma membrane. It lies in contact with the wall. Pollengrain grows in size. The cytoplasm begins to become vacuolated. Formation of vacuoles pushes the nucleusto one side near the pollen grain wall. The protoplast undergoes mitosis. Due to peripheral position ofnucleus, the protoplast of pollen grain divides unequally into two cells—a large tube or vegetative cell andsmall generative cell. Tube cell or vegetative cell contains small vacuoles, cell organelles and reserve foodof all types–starch, proteins and lipids. Fatty acids are mostly unsaturated. Slowly, its nucleus becomeslarge and irregular. Generative cell is lenticular to spherical in outline. It has a thin layer of cytoplasmaround a compact nucleus. A layer of callose develops around the generative cell. It helps in separation ofgenerative cell from the wall of pollen grain. Later on, the callose covering of generative cell dissolves.The freed naked generative cell comes to lie freely in the cytoplasm of tube or vegetative cell. In over60% of flowering plants, the pollen grains are shed in 2-celled stage. In nearly 40% others, thegenerative cell divides further into two male gametes. In such cases pollen grains are shed in three-celledstage (1 tube cell +2 male gametes).

Differences Between Generative and Vegetative Cell

Generative Cell Vegetative Cell

1. It is the smaller cell of male gametophyte.

2. Generative cell consists of a compact nucleusand a thin layer of cytoplasm.

3. It forms two male gametes.

1. It is the larger cell of the male gametophyte.

2. Tube cell has an irregular nucleus and largevacuolated cytoplasm having reserve food.

3. It forms pollen tube that carries the malegametes for fertilization.

��/'�)��%"#('!� #�� )#0�" �&��)��$ 1�2. Post-Pollination Development. Further growth of pollen grain occurs on the stigma. In case of

compatible pollen, the tube cell absorbswater and nutrients from stigma throughgerm pores or germinal furrows. It swellsup and comes out from one of the germpores or germinal furrows as pollen tube.Pollen tube contains not only the contentsof tube cell but the generative cell alsodescends into it. However, it soon dividesto form two male gametes. Pollen tube iscovered by only intine. It secretespectinases and other hydrolytic enzymesfor making its passage through the style(if it is solid) and for getting nourishmentfor its growth. As the pollen tube grows,only the terminal part comes to have densecytoplasmic contents, degenerating tubenucleus and two male gametes. Theremaining part of the tube becomes highlyvacuolated and separated by calloseplugs. The male gametes are also calledsperm cells. They are lenticular to spherical in outline. Each male gamete has a large nucleus surroundedby a sheath of cytoplasm and covered over by a distinct plasmalemma.

The fully mature male gametophyte consists of three cells – two male gametes and a tube cell forminga long pollen tube. Usually, there is a single pollen tube and such a pollen grain is called monosiphonous.However, in the members of family Malvaceae (Althea, Malva) and Cucurbitaceae (Luffa), there are asmany as 14 pollen tubes per pollen grain. This condition is called polysiphonous.��" ��#�� $%�� &� �!��

Female reproductive organs of the flower are carpels, collectively called gynaecium or gynoecium. Itmay have a single carpel (monocarpellary), two carpels (bicarpellary), several carpels (multicarpellary orpolycarpellary). When more than one, the carpels may be free (apocarpous) or fused (syncarpous). Free unitof gynoecium is called pistil. Each pistil has 3 parts.

(i) Ovary. It is basal swollen ovule containing region. Ovary has an ovarian cavity which may haveone to many chambers called locules (= loculi). Ovule bearing cushions or placentae (singular placenta)occur in the ovarian cavity. Number of ovules in an ovary may be one (e.g., Wheat, Paddy, Mango,Sunflower) to many (e.g., Papaya, Water Melon, Orchids).

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�Fig 2.12. Pistils. A, multicarpellary, syncarpous pistil with free stigmas of Hibiscus. B, multicarpellary,syncarpous pistil of Papaver. C, multicarpellary apocarpous pistils of Michelia.

�Fig. 2.11. Formation of male gametophyte in angiosperms.

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Differences Between Apocarpous and Syncarpous Ovary

S.No. Apocarpous Ovary

1. The ovary is formed from a single free carpel.

2. The flower bears one to several free pistils.

3. Ovary is unilocular.

4. It occurs only in primitive families.

5. The fruit is simple in unicarpelled flowers oraggregate in polycarpelled flowers.

�� $%�� Ovule is an integumented, indehiscent, megasporangium which after fertilization is induced to develop

into seed. Ovules of angiospermic plants are stalked, oval and whitish structures. They are borne over aparenchymatous cushion or placenta present inside the ovary. The number of ovules present in an ovary maybe one (e.g., Wheat, Rice, Mango) to many (e.g., Papaya, Water Melon, Orchids). The attachment is bymeans of stalk of ovule called funiculus or funicle. The point of attachment of funiculus to the body ofovule is known as hilum. In typical inverted or anatropous ovule, funiculus is fused lengthwise beyondhilum to form a ridge called raphe. Funiculus is vascular (i.e., with xylem and phloem) to supplynourishment. Main body of ovule is composed of parenchymatous mass called nucellus (= megasporangium).It generally encloses a single embryo sac or female gametophyte. The cells of nucellus are rich in reservefood. Nucellus may be thin (tenuinucellate, e.g., Asteraceae or Compositae) or massive (crassinucellate,e.g., Casuarinaceae). Nucellus is surrounded by 1-2 multicellular cutinised coverings called integuments.Ovule is called unitegmic if it is covered by a single integument (higher dicots, e.g., Asteraceae) andbitegmic if there are two integuments (monocots and lower dicots like Malvaceae and Brassicaceae). Arare condition is tritegmic or presence of three integuments, e.g., Asphodelus. Ovules are naked or ategmicin members of parasitic families, e.g., Santalum, Loranthus. Inner region of integument may providenourishment to developing embryo sac when it is called as endothelium. Outer side of each integument aswell as nucellus is covered with cuticle (Fahn, 1967).

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�Fig. 2.13. L.S. of an ovule.

Syncarpous Ovary

The ovary is formed from fusion of two or morecarpels.

The flower bears a single pistil.

Ovary can be uni to multilocular.

It occurs in most of the families.

The fruit is generally simple.

��/'�)��%"#('!� #�� )#0�" �&��)��$ 1+Part of the ovule from which the integuments develop is called chalaza. Integuments do not cover the

ovule completely. A pore is left at one end. The pore or passage present at the tip of integuments is calledmicropyle. Area below the micropyle represents the micropylar pole. Ovule arises as a mound ofmeristematic primordium over the placenta. It produces a nucellus. Initials of integuments develop from itsbase. Integuments grow and cover the nucellus except for micropyle. Base of the mound elongates and formsthe funiculus. A hypodermal cell in the micropylar region of nucellus differentiates into primary archesporialcell. Primary archesporial cell divides periclinically into outer primary parietal cell and inner primarysporogenous cell. Usually the primary parietal cell does not divide further. It, however, forms a smallparietal tissue in primitive angiosperms like Casuarina. Primary sporogenous cell generally functionsdirectly as megaspore mother cell. In primitive angiosperms it may form a small sporogenous tissue.

Megasporogenesis. It is the process of formation of haploid megaspores from diploid megaspore mothercell or MMC. Generally a single megaspore mother cell differentiates in the micropylar region of nucellus.It is distinct from the rest of nucellar cells by its larger size, dense cytoplasm and prominent nucleus.Megaspore mother cell (MMC) undergoes meiosis and forms four haploid megaspores arranged generallyin the form of a linear tetrad. Commonly one megaspore is functional. It behaves as the first cell of femalegametophyte. The functional megaspore is generally chalazal one but is micropylar in Balanophora. Any ofthe four cells can be functional in Casuarina. The nonfunctional megaspores degenerate.

Differences Between Microsporogenesis and Megasporogenesis

S.No. Microsporogenesis

1. It is formation of haploid microspores or pollengrains from diploid microspore mother cell.

2. It occurs inside microsporangium or pollen sacof an anther.

3. There are numerous microspore mother cells ina microsporangium.

4. The four microspores formed from a singlemicrospore mother cell are generally arranged ina tetrahedral tetrad.

5. All the products of microsporogensis arefunctional.

6. The products of microsporogenesis or microsporesgive rise to male gametophytes.

Formation of Female Gametophyte or Embryo Sac. �� The functional megaspore grows in size. It undergoes three free nuclearmitotic divisions. Initially the megaspore nucleus divides mitotically into two. The two nuclei move toopposite poles forming two-nucleate stage of embryo sac. Both the nuclei undergo two sequential mitoticdivisions producing first a four nucleate stage and then an eight nucleate stage of embryo sac. Two groupsof four nuclei each develop in the two halves or ends. One nucleus from each group passes towards thecentre. They are called polar nuclei. Soon cell walls are laid down. Seven cells are formed, a largebinucleate central cell and three cells at each pole. The embryo sac is, therefore, seven celled and eightnucleate. It is surrounded by common membrane derived from megaspore wall. Maheshwari (1950) hasdescribed ten types of embryo sacs. They are of three categories—monosporic (from one functionalmegaspore), bisporic (from one dyad or a cell formed from first meiotic division) and tetrasporic (from allthe four nuclei formed after complete meiosis). The most common embryo sac is monosporic, polygonumtype. It is 8-nucleate but seven celled.

Embryo Sac (Female Gametophyte). It is an oval multicellular structure which is embedded in thenucellus. The embryo sac is covered by a thin pectocellulosic layered membrane (Chebotaru, 1975) derivedfrom the wall of functional megaspore. Embryo sac generally contains seven cells—one large central, threemicropylar and three chalazal. Micropylar cells form a complex called egg apparatus. The chalazal cellsare called antipodal cells. All the cells are interconnected through plasmodesmata.

Megasporogenesis

It is the formation of haploid megaspores fromdiploid megaspore mother cell.

It occurs inside megasporangium or ovule.

There is generally a single megaspore mother cellin a megasporangium.

The four megaspores formed from a megasporemother cell are commonly arranged in the form ofa linear tetrad.

Only one megaspore in functional. Othersdegenerate.

The functional product of megasporogenesis formsthe female gemetophyte or embryo sac.

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(i) Egg Apparatus. It is a grouping of three micropylar cells of embryo sac. The cells are arranged inthe form of a triangle with a middle oosphere and two lateral synergids. All the cells are pyriform inoutline. Synergids or help cells have lateral hooks, terminal filiform apparatus and a wall that is thintowards the chalazal end. The cytoplasm is vacuolated towards chalazal end. Nucleus lies in the middle.Synergids have a number of roles : (i) Absorption of nourishment from nucellus. (ii) Secreting chemotacticallyactive substances from its filiform apparatus for guiding pollen tube (Ishikawa, 1918). (iii) Acting as shockabsorber for ingrowing pollen tube. (iv) Forming seat for pollen tube discharge.

Egg or oosphere is larger than the synergids. It represents the female gamete. Wall is thick towardsthe micropylar end which gradually thins out towards the broad chalazal end. Filiform apparatus may ormay not be present. Vacuole is present in micropylar region. Nucleus is central. Cytoplasm is dense in thechalazal end.

(ii) Antipodal Cells. They are three cells present in the chalazal end of embryo sac. Antipodal cellsvary in shape and size. They may become multinucleate due to endopolyploidy and polyteny. The cellspossess a number of enzymes, starch, lipids and proteins. Antipodal cells are vegetative cells of embryo sacwhich seem to take an active part in absorbing nourishment from nucellus. The cells may develop haustoriafor obtaining nourishment. They ultimately degenerate.

�Fig. 2.14. Different stages of megasporogenesis and development of embryo sac.

(iii) Central Cell. It is the largest cell which is bounded bymembrane of embryo sac. Central cell has 2 polar nuclei, a vacuolated

cytoplasm rich in golgi bodies and reserve food. The two polarnuclei often fuse in centre to form a single diploid secondary orfusion nucleus (= definitive nucleus). It is the only diploid structure

in the embryo sac which later on gives rise to primary endospermcell.

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��/'�)��%"#('!� #�� )#0�" �&��)��$ 11Differences Between Male and Female Gametophytes

S.No. Male Gametophyte Female Gametophyte

1. It develops from microspore or pollen grain. It is formed from megaspore.

2. It is not retained inside the microsporangium. It is retained permanently inside the megasporangium.

3. Development occurs in two stages, pre-pollination Development is completed in a single stage prior to

and post-pollination. fertilization.

4. Male gametophyte comes out of the confines of It remains within the confines of the megaspore.

the microspore.

5. Growth of male gametophyte is completed over Growth is completed in situ.

the female reproductive organ and is meant for

sending the male gametes into the female gametophyte.

6. It has three cells (1 tube cell + 2 male gametes). It has seven cells (3 antipodals + 1 central cell +1 oosphere + 2 synergids)

7. All the cells are essential. The two male gametes take All the cells are not essential. Oosphere and central

part in double fertilization while tube cell is required cell are involved in double fertilization. Only one

to form pollen tube for carrying the male gametes. synergid receives the pollen tube. Antipodal cells

may be ephemeral or help in absorption of nourishment.

8. After fertilization, the remains of male gametophyte After fertilization, there is active growth of endosperm

degenerate. and embryo.

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Both the male gamete and female gamete are non-motile. Fertilisation can occur only when the twoare brought together. This is done through pollination. Pollination is the process of transfer of pollengrains from anther (or microsporophyll) and their deposition over the stigma (receptive region ofmegasporophyll) of a flower. Such a pollination is also called indirect pollination. In gymnosperms astigmatic surface is absent. Pollen grains reach the micropylar canals of the ovules. Such a mode ofpollination is called direct pollination. Pollination can occur through contact due to growth or gravityand an external agency like wind, water or animals. Depending upon genetic similarity and dissimilarity

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between anther and stigma, pollination is of two types, self pollination and cross pollination. Crosspollination is also known as xenogamy. Self pollination is of two types, autogamy and geitonogamy.Therefore, there are actually three types of pollination – autogamy, geitonogamy and xenogamy.��

It is the transfer of pollen grains from anthers to the stigma of same or genetically similar flower. It is

possible only when anthers and stigmas mature simultaneously. Self pollination is of two types, autogamy

and geitonogamy.

1. Autogamy (Gk. autos—self ; gamos—marriage). It is self pollination which occurs between anther

and stigma of the same flower. It occurs in all those intersexual or perfect flowers which either remain

closed or where anthers/pollen come in contact with stigma by gravity and mechanical means. Autogamy is

of the following types :

(i) Homogamy. The flowers are open or chasmogamous. Both anthers and stigmas are close together.

They mature simultaneously with synchrony in pollen release and stigma receptivity. (a) In Convolvulus,

Catharanthus (= Vinca) and Gardenia, the anthers occur in the neck of corolla tube. As the style grows, the

stigma comes in contact with ripe anthers and receives

the pollen grains. (b) In Lilac, the style does not grow

and the stigma remains below the level of anthers. As

the anthers dehisce, the pollen fall down due to gravity

over the surface of stigma.

(ii) Cleistogamy (Gk. kleisto—closed, gamos—

marriage). The flowers remain closed with anthers and

stigma lying close to each other. When the anthers

dehisce, the pollen grains come in contact with stigma

and pollination takes place. Cleistogamy ensures self

pollination as there are no chances of cross pollination.

It also ensures seed set even in the absence of

pollination. In Commelina bengalensis and Arachis

hypogea (Groundnut) cleistogamy is accompained by

geocarpy, i.e., formation of fruits inside the soil. Inothers, cleistogamous flower remains above ground, e.g.,Balsam, Oxalis, Viola (Common Pansy). In majority ofcases, flowers are chasmogamous in the beginning offlowering season but become cleistogamous later in orderto ensure fruit formation. Commelina bears bothchasmogamous and cleistogamous f lowerssimultaneously but in different positions (Fig. 2.17.)

Differences Between Chasmogamy and Cleistogamy

S.No. Chasmogamy Cleistogamy

1. It is a condition of opening of mature flowers. It is a condition of keeping the flowers closedthroughout.

2. The flowers are conspicuous. The flowers are small and inconspicuous.

3. Both self and cross pollination can occur. Only self pollination is possible.

4. Both external and internal factors are involved Only internal factors take part in pollination.

in effecting pollination.

5. It is a normal condition. It is a fail-safe device.

�Fig. 2.17. Chasmogamous and cleistogamousflowers of Commelina.

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(iii) Bud Pollination. Anthers and stigmas of an intersexual or perfect flower mature before theopening of a flower. If causes self pollination inthe bud condition, e.g., Pea, Jute, Rice, Linseed,Tomato, Tobacco, Wheat.

(iv) Fail-safe Device (Mechanical Device).In several plants, self pollination occurs whencross pollination fails. The phenomenon is calledfail-safe device. In Potato the stigma bends overthe anthers, whereas in Sunflower stigma cancurl back to receive pollen present on thebrushing hair. In Mirabilis (4 O’Clock) theanthers bend over the stigma for pollination.

2. Geitonogamy (Gk. geiton—neighbour,gamos—marriage). It is the transfer of pollengrains from anthers of one flower to stigma ofanother flower of either the same (endogamy)or genetically similar plant. Geitonogamyresembles cross pollination in the requirement of pollen transfer through a pollinating agency. Therefore, itis functionally cross pollination but genetically it is similar to autogamy, e.g., Cucurbita.

Differences Between Autogamy and Geitonogamy

S.No. Autogamy Geitonogamy

1. It is transfer of pollen grains from anther to It is transfer of pollen grains from anther of one

the stigma of the same flower. flower to the stigma of another flower of the sameplant.

2. The flowers are hermaphrodite. The flowers are generally unisexual.

3. No external agency is required for pollination. An external agency is required to performpollination.

'��Advantages

1. It is a sure and economical method of pollination.2. Self pollination is employed as fail-safe device.3. It produces homozygous progeny.4. Self pollination is used to maintain pure lines.5. It maintains superiority of the race indefinitely.6. The plants need not produce large number of pollen grains.7. Flowers do not develop attractants for favouring external agencies.8. Harmful and useless characters are eliminated naturally.

Disadvantages

1. No new traits are introduced.2. It decreases variability and adaptability to changes in environment.3. Disease resistance decreases with time.4. Recessive traits appear regularly as self pollination introduces homozygosity.5. There is no way to eliminate defective traits.

6. Yield decreases with time due to reduction in vigour and vitality.

�Fig. 2.18. Two devices for self pollination.A, Mirabilis. B, Potato.

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(��%�� (i) Bisexuality. Flowers are intersexual or hermaphrodite.

(ii) Homogamy. Anthers and stigma mature simultaneously.

(iii) Contact Pollination. The pollen grains of the mature anther fall over the receptive stigma eitherby gravity or direct contact due to mechanical disturbance and growth.

(iv) Cleistogamy. Flowers remain closed.

(v) Bud Pollination. Pollination occurs before the opening of flowers.(�� )��!

It is the transfer of pollens from anther of one flower to the stigma of another flower belonging togenetically different plant. Cross pollination is also called xenogamy (Gk. xenos—strange; gamos—marriage).Both xenogamy and geitonogamy are included under allogamy (Gk. allos—other; gamos—marriage) throughmany authors consider allogamy as synonym of xenogamy. Cross pollination can occur only with the help ofexternal agents called pollinating agents or agencies. The latter are of two types, abiotic and biotic.Abiotic agents are wind and water. Here it is mere a chance factor that pollen grains come in contact withreceptive stigma. Therefore, flowers produce enormous amount of pollen as compared to fewer number ofovules. Majority of the plants use biotic agents for pollination. Biotic agencies are animals like insects,birds, bats, snails, ants, etc. The type of cross pollination is named after the agent like anemophily (windpollination), hydrophily (water pollination), entomophily (insect pollination), malacophily (snail pollination),myrmecophily (ant pollination), chiropterophily (bat pollination) and ornithophily (bird pollination).

Differences Between Geitonogamy and Xenogamy (Allogamy)

S.No. Geitonogamy Xenogamy

1. It performs self pollination. It performs cross pollination.

2. Geitonogamy occurs between two flowers Xenogamy occurs between two flowers of different

of the same plant. plants.

3. Pollination occurs between genetically sim- Pollination occurs between genetically dissimilar

ilar flowers. flowers.

4. It produces fewer variations. It produces a lot of variations.

1. Anemophily (Gk. anemos—wind ; philein—to love). It is a mode of cross pollination performed

through the agency of wind. Anemophily is more common of the two abiotic pollinations. Air currents pickup pollen grains from the dehiscing anthers and carry the same to different places. Receptive stigmas pickup the pollen floating in the air.

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often numerous and packed in inflorescence.(ii) Non-essential floral parts are reduced or absent.

(iii) Flowers are usually colourless, nectarless andodourless.

(iv) Flowers are developed above the foliage, usuallyin hanging spikes or catkins.

(v) Male flowers are more abundant in case ofunisexual flowers. In bisexual flowers stamens aremore abundant.

(vi) Anthers are exserted and versatile.(vii) Anthers burst forcefully and suddenly to throw the

pollen grains in air as in case of Urtica. It is calledgunpowder mechanism.

�Fig. 2.19. Feathery Stigma andversatile anthers in Grass.

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��/'�)��%"#('!� #�� )#0�" �&��)��$ 15(viii) Pollen grains are small, smooth, nonsticky and light. They may have air sacs or wings. Such

pollens can float in air for long distances, upto 1300 km in Pine.(ix) Pollen grains are dry and unwettable. This protects the pollen from moisture present in the air.(x) Stigmas are exserted, hairy, feathery or branched to capture the pollen grains. The cob of Maize

has elongated stigmas and styles which sway in wind to trap pollen grains.(xi) A very large number of pollen grains are produced, e.g., 500000 per flower in Cannabis, 25

million by a tassel of Maize and 135 million by Mercurialis.(xii) Pistils commonly possess single ovules.Examples. Anemophily is common in grasses. Other examples are Amaranthus, Cannabis, Chenopodium,

Coconut, Date, Mulberry, Poplar, Willow, etc.� &� 8 !��!�

(i) It is a highly wasteful phenomenon because it is non-directional.(ii) Rate of successful pollination is low.

(iii) Air borne pollen of some plants cause hay fever and bronchial allergy.

� Bronchial Allergy. Inhalation of pollen grains which act as allergens, cause difficulty inbreathing by narrowing the respiratory tract.

� Poisonous Pollen. Serjania lethalis.

2. Hydrophily (Gk. hydor—water ; philein—to love). It is pollination brought about through theagency of water. It occurs in about 30 genera of mostly monocotyledonous aquatic plants, e.g., Lemna,Vallisneria, Ceratophylum, Zostera. Many aquatic plants use other modes of pollination (e.g. WaterHyacinth, Water Lily) because water is not a good transport medium for pollen grains. They emerge outof water and are pollinated by wind or insects. Many workers believe that distribution of bryophytes andpteridophytes is limited because of the dependence of their sperms on water for transport.

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�Fig. 2.20. Pollination in Vallisneria.

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�7�"�!��" $� !$�#8�9-("#%7 )#'$��)#0�"$(i) Flowers are small, inconspicuous and light.

(ii) Perianth is unwettable.(iii) Flowers are without nectar and odour.(iv) Light and unwettable pollen grains. They are generally surrounded by mucilaginous covering.(v) Long, sticky and unwettable stigma.

Types. Hydrophily is of two types—hypohydrophily and epihydrophily.

(i) Hypohydrophily. Pollination takes place below the surface of water. e.g., Ceratophyllum, Zostera(Sea Grass).

(a) Ceratophyllum. It is submerged fresh water plant having both male and female flowers. Maleflower has 30–45 stamens. On maturation anthers break, rise to the surface and release pollen grains.Pollen grains are small, rounded, thin walled and without exine. They slowly sink downwardly to effectpollination. Stigma is quite long and sticky.

(b) Zostera (Sea Grass). It is marine angiosperm. Pollen grains are long and ribbon-like, upto 2500 �min size. Exine is absent. The filamentous pollen grains float below the surface of water as they have aspecific gravity exactly similar to that of water. Stigmas are also quite long. The two have a fair chance tocome in contact for pollination.

(ii) Epihydrophily. Pollination takes place on surface of water e.g., Lemna, Vallisneria.

Vallisneria (Tape Grass or Eel Grass). It is submerged, dioecious, fresh water plant. Male plantproduces a large number of male flowers which after breaking, rise upward in closed state and open on thesurface of water. Each male flower has two functional stamens, two tepals forming boat like structure whilea third small upwardly bent tepal forms a sail. Female plant produces female flowers singly at the tip oflong pedicels that bring the flowers on the surface of water. Stigma is trifid. During floating, male flowersare drawn in the depression of female flower. Ripe anthers of open male flowers come in contact with largetrifid stigma of the female flower to effect pollination. After the pollination, female flower closes again. Itis brought down into water by coiling of stalk.

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�Fig. 2.21. Male and female flowers of Vallisneria.

Zoophily. It is a mode of pollination in which the biotic agency of animals is used for transfer ofpollens from anthers of one flower to the stigma of another flower. Zoophily has several subtypes—entomophily, malacophily, chiropterophily, ornithophily, myrmecophily and anthrophily. There are alsoreports of other animals carrying out pollination, e.g. Gecko Lizard, Garden Lizard (reptiles), arboreal(tree dwelling) rodents, lemurs (primates).

3. Entomophily. It is transfer of pollen grains from anthers of one flower to the stigma of anotherflower with the help of insects like moths, bees, wasps, butterflies, beetles, ants, flies, etc. Beetles werethe earliest insect pollinators. Bees are the most common pollinating insects. Insects visit flowers forobtaining food (pollen, nectar) or shelter. Some insects also use flowers for laying eggs, e.g., Amorphophallus.Amorphophallus has the largest inflorescence and the tallest flowers with a flower reaching about 1·8 m (6feet). While picking up food, the insect visitor deposits pollen grains brought from some other flower overthe stigma and gets dusted afresh with pollen grains from the present flower. However, all insect visitors

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are not pollinators. Some of them visit flowers only for pollen and nectar. They are called pollen/nectarrobbers.

( �� &�� *��(i) Flowers are coloured for attracting the insects. Moths are attracted towards the white flowers.

Reddish flowers attract butterflies and wasps. Honey bees are attracted towards the bluish-purplish-violet-yellow flowers which appear coloured in ultra-violet vision of bees. Honey bees rarely visit a red flowerbecause it appears black in ultra-violet radiations.

(ii) Both sepals and petals are well developed.

(iii) Petals are usually coloured. Where petals are not showy, other flower parts become conspicuous,e.g., coloured bract in Bougainvillea, involucre in Euphorbia and Poinsettia, coloured leaves in Euporbiapulcherrima, spathes in arioids, one sepal enlarged in Mussaenda, stamens in Callistemon (Bottle Brush),Acacia and Mimosa.

(iv) Flowers are generally large in size so that they become conspicuous from a distance. Whereflowers are small in size, they are aggregated to form conspicuous groups.

(v) Flowers commonly produce odour. It can be pleasant (Jasmine, Rose, Mustard, Chameli, Champa)or foul (Aristolochia, Arum, Rafflesia). Foul odour attracts flies and beetles. Foul smell of Rafflesia(largest flower) attracts carrion flies for pollination.

(vi) Majority of flowers have landing platform for insects.

(vii) Special markings are present on petals to guide the insects to nectar. They are called nectarguides or honey guides, e.g., Viola.

(viii) Visiting insects are fed by either nectar as in case of Adhatoda, Buttercup, Jasmine, Bottle Brushand Larkspur or edible pollen as in Magnolia, Papaver, Rosa and Clematis. Bees visit flowers forobtaining both nectar and edible pollen. They have special sacs for gathering pollen. The same are calledpollen baskets.

Some flowers provide shelter to pollinators. Others provide them safe place to deposit eggs, e.g.,Amorphophallus. Amorphophallus has the tallest flower, some six feet in height. Yucca and its pollinating

moth Pronuba cannot complete their life cycles without each other.

(ix) Pollen grains are covered by a yellow sticky substance called pollenkitt.

(x) Pollen grains are spiny and heavy.

(xi) Normally stamens are inserted except when they take part in insect attraction, e.g., Mimosa.

(xii) Stigma is inserted and sticky.

(xiii) Flowers and their petals are strong enough to bear the weight of visiting insects.

&�� +��(i) Calotropis (Ak). Pollinia of Calotropis form translators. They can be lifted and transferred to the

stigma of another flower only with the help of insects.

(ii) Salvia. It has turn pipe or lever mechanism for pollination by insects. Flower is protandrous withtwo functional stamens. Corolla is bilipped. The lower lip functions as a platform for visiting insects.Upper lip encloses essential organs. Each stamen bears long connective with fertile anther lobe at one endand flat sterile anther lobe at the other end. Flowers possess nectar at the base of ovary. When an insectvisits young flower, the plate like sterile anther lobe is pushed inwardly while the fertile anther lobe strikesthe back of insect to throw pollen there. In old flower the stamens wither. The style elongates and bends themature stigma to pick pollen grains from the back of the insect.

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�Fig. 2.22. Pollination in Salvia.

(iii) Fig (Ficus carica). Fig is totally dependent upon Blastophaga (Wasp) for pollination. The waspdepends upon fig for food and survival. Fig possesses hypanthodium inflorescence with female flowers atbase and male flowers near the pore while gall flowers occur between the two. An impregnated femalewasp visits a hypanthodium to lay eggs into the gall flowers. Simultaneously, it brings pollens from anotherhypanthodium for pollinating female flowers. Grubs coming out of the eggs feed on gall flowers, grow andcome out of the hypanthodia laden with pollen grains from male flowers.

(iv) Yucca. It is pollinated by a moth called Pronuba (= Tageticula) yuccasella. Both are dependentupon each other for survival. Insect deposits eggs in the ovary of yucca flower. On entering a flower, mothundergoes rotational movement. This deposits pollen grains over the hollow stigma of the same flower. Asthe seeds start developing, the larvae of the moth hatch out of eggs.

(v) Ophrys. The flowers of Mediterranean orchid Ophrys resemble in shape, colour and odour tofemale of wasp Colpa aurea, thus showing mimicry. The male wasps try to copulate with them(pseudocopulation) and in the processs pollinate the flowers.

Differences Between Anemophilous and Entomophilous Flowers

S.No. Anemophilous Flowers Entomophilous Flowers

1. Flowers are generally small. Flowers are generally large.

2. They are inconspicuous. They are conspicuous from a distance.

3. Bright colouration is absent. The flowers are brightly coloured to attract insects.

4. Flowers are without smell. Flowers have specific odour for attracting particular typeof insects.

5. They do not produce nectar. Most entomophilous flowers produce nectar for visitinginsects.

6. Pollen grains are not edible. Some flowers have edible pollen.

7. Sepals and petals are either small or absent. Sepals and petals are quite prominent.

8. Anthers are exserted. Anthers are generally inserted. Rarely they are exserted

and coloured to attract insects.

9. Anthers are versatile. Anthers have fixation other than versatile.

10. Stigma is exserted. Stigma is inserted.

11. Stigma is feathery or branched to entangle Stigma is commonly unbranched and sticky.

pollen grains.

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13. Pollen grains are small and light. They are larger and heavier.

14. Pollen grains are unwettable. Pollen grains are sticky.

15. Anemophily is non-directional. Entomophily is highly directional.

4. Ornithophily (Gk. ornis—bird ; philein—to love). It is cross pollination performed through theagency of birds. Pollinating birds have long beaks, larger than the length of the corolla tube. Two

specialised types of pollinating birds of tropics are sun birds and humming birds. Sun birds (e.g.,Nectarinia species) are found in Afro-Asian region. They rest over the flower bearing shoot while visitingthe flowers. Humming birds occur in American continents. They do not sit over the flowers or their

supporting shoots but instead hover over the flowers. Both sun birds and humming birds are small-sized. Afew birds of larger size also perform ornithophily, e.g., Myna, Parrot, Bulbul, Crow. Some commonornithophilous plants are Bignonia, Tecomaria (Honey Suckle), Butea monosperma (Flame of Forest),

Erythrina (Coral Tree), Grevillea (Silver Oak), Callistemon (Bottle Brush, also by bees), Bombax (Red SilkCotton), Agave (Century Plant), etc.

Characteristics of Ornithophilous Flowers. (i) Flowers are large sized. (ii) They are brightlycoloured with yellowish, orange, reddish or bluish colour. (iii) Odour is generally absent. (iv) Corolla isoften funnel shaped. (v) Floral parts are strong and leathery. (iv) Flowers secrete a lot of nectar so much so

that shaking of Erythrina and Grevillea shoots will result in falling of nectar drops. Nectar is watery withabundant sugar. A humming bird may suck nectar equivalent to half its body weight per day.

5. Chiropterophily or Cheiropterophily (Gk. cheir—hand, pterous—wing, philein—love). It is crosspollination performed through the agency of bats. Bats perform pollination during night as they are nocturnal

in habit. They visit flowers for nectar. In the process they carry pollen grains from one flower and depositthe same over the stigma of another flower. The distance travelled by pollinating bats may be 30 km ormore. Some common cheiropterophilous plants areAnthocephalus (Kadamb), Bauhinia megalandra, Adansonia

(Baobab tree), Kigelia pinnata (Sausage tree).

Characteristics of Cheiropterophilous Flowers. (i)Flowers are stout and large sized. (ii) They are dullcoloured with strong fruity odour. (iii) Flowers secreteabundant dilute nectar. (iv) Stamens arenumerous. Adansonia bears 1500-2000 stamens perflower. (v) Pollen grains are abundant.

6. Malacophily (Gk. malakos—soft, philein—to love).It is cross pollination performed through the agency ofsnails. Malacophily occurs in Arisaema (Snake or CobraPlant), Arum lilies and some other aroids. The spadicesprovide shelter to snails.

7. Myrmecophily. It is cross pollination carried outby ants.

8. Anthrophily (Controlled pollination). It is artificialpollination performed by human beings during breedingexperiments amongst selected varieties. Pollen grains arecollected in small pockets from the male parent. Thesame are dusted over the stigma of the female parent withthe help of an uncontaminated brush. Artifical pollinationor anthropophily has been carried out in case of DatePalm since prehistorical periods. �Fig. 2.23. Pollination by Humming Bird.

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$�� ,�%�� ,�%�� (�� The following six types of devices promote and ensure outbreeding through cross pollination :

1. Unisexuality (Dicliny). Flowers are unisexual or diclinous. Plants may show monoecy (monoeciouswith both male and female flowers occuring in single individual, e.g., Maize, Castor) or dioecy (dioeciouswith male and female flowers on different plants, e.g., Mulberry, Papaya, Date Palm). Monoecy preventsautogamy but not geitonogamy. Dioecy prevents both autogamy and geitonogamy. Usually cross pollinationis performed.

2. Dichogamy (Gk. dicha—in two, gamos—marriage). Here, in a bisexual flower, anthers and stigmasmature at different times, so that self pollination is inhibited. Dichogamy is of two types.

(a) Protandry. Anthers mature earlier than stigma, e.g., Clerodendron, Salvia, Sunflower, Rose.

(b) Protogyny. Stigma matures earlier than anthers, e.g., Gloriosa, Magnolia, Mirabilis, Plantago.

3. Self Sterility (= Self Incompatibility). Pollen grains of one flower are incapable of growing over thestigma of the same flower due to the genetic mechanism of presence of similar sterile genes, e.g., S1 or

S2 in pollen grains and S1 S2 in stigma. Self sterility occurs in Crucifers, Potato, Tobacco, Gramineae,Orchidaceae.

4. Prepotency. Pollen grains of one flower grow more rapidly over the stigma of another flower as

compared to the same flower, e.g., Apple, Grape.

5. Heterostyly. Flowers have different types of height of styles and stamens. Heterostyly is of followingtypes :

(i) Diheterostyly (Dimorphic Heterostyly). There are two types of flowers : (a) Pin Eyed. Long style,short stamens. (b) Thrum Eyed. Short style, long stamens, e.g., Jasmine, Primula (Primrose).

(ii) Triheterostyly (Trimorphic Heterostyly). There are three types of flowers : (a) Long style, stamensmedium and short height. (b) Style medium, stamens long and short height. (c) Style short, stamens long andmedium height, e.g. Lythrum, Oxalis.

In heterostyly, pollination occurs between anthers and stigmas of the same height, which condition isfound in different flowers so that cross pollination is effected.

6. Herkogamy. They are mechanical devices that prevent self pollination and favour cross pollinationeven in homogamous flowers, e.g.,

(i) Occurrence of extrorse anthers.

(ii) In Gloriosa and Clerodendron, the mature stigma and anthers occur in different positions.

(iii) In Pansy, anthers are exposed while stigma occurs inside a flap.

(iv) In Kalmia, the stigma is exposed but anthers occur inside corolla pockets.

(v) In Salvia, there is lever mechanism or turn pipe mechanism to shed pollen grain at the back ofvisiting insect.

(vi) In Calotropis and many orchids pollen grains occur in sacs called pollinia. Two adjacent polliniaare attached to a common sticky corpusculum to form a translator. Translator can be lifted by insectsonly.

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pit fall flowers as the attracted flies once inside the flowers cannot come out, till the anthers mature andthe deflexed hair present in the corolla tube wither. This ensures the carrying of pollen grains by the flies toother flowers.

'�� (��Advantages

1. It overcomes self-sterility and promotes prepotency found in many economically important plants.For this, orchardists grow two or more varieties of plants in order to ensure better yield.

2. Yield always remains above an average minimum.3. It eliminates defective traits. The harmful recessive traits remain unexpressed due to phenomenon

of heterozygosity.4. It introduces a number of alleles.5. Cross pollination introduces variations due to genetic recombinations.

6. It may produce better offspring than either of the parents due to phenomenon of hybrid vigour orheterosis.

7. Cross pollination is used to produce new varieties of plants.8. It increases resistance to diseases.9. Cross pollination enhances adaptability of the offspring to changes in the environment.

10. The offspring formed after cross pollination are better fitted in the struggle for existence.Disadvantages

1. It is highly wasteful process, because of the large number of contrivances required to ensure it.2. For cross pollination by any agency, a chance factor is always there.3. It is not an economical phenomenon for plant.4. Good characters of a race can be diluted.5. Undesirable characters will enter in the progeny.

(�� -��In nature, cross pollination is preferred over self pollination because (i) It keeps variability of race.

(ii) It makes offspring adaptable to changes in environment. (iii) Production of better offspring due tophenomenon of hybrid vigour. (iv) It does not allow harmful and lethal recessive alleles to becomehomozygous.

.��1. Pollination is a pre-requisite for fertilization in flowering plants. 2. It brings in male gametes for

fertilization. 3. It stimulates growth of ovary. 4. Premature abscission of ovary is prevented. 5. Pollengrains bring in hormones not only for their own growth but also growth of the ovary. 6. Pollination helps inproduction of seeds and fruits. 7. Seeds and fruits ensure continuity of the plant species. 8. Seeds and fruits area source of nutrition to several animals as well as human beings. 9. Pollination helps in gene recombinations.10. Cross pollination produces offspring with combination of characters from two types of varieties or races.It helps in development of hybrid seeds.

Differences Between Self and Cross Pollination

S. No. Self Pollination Cross Pollination

1. It does not require any external agency. An external agency is required for performingcross pollination.

2. There is transfer of pollen from anthers There is transfer of pollen grains from the anthersto the stigma of the same or genetically of one flower to the stigma of a geneticallydifferent similar flower. flower.

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3. It cannot produce a new race or variety. Cross pollination is used in the formation of newraces and varieties.

4. Flowers are intersexual or hermaphrodite. Flowers may be unisexual or intersexual. 5. Both anthers and stigmas mature at the Anthers and stigmas generally mature at different

same time. times. 6. Flowers can be open or closed. Flowers are always open. 7. It is used as fail-safe device. It is a normal process of pollination. 8. It does not require any special structure. It requires a number of special structures for

ensuring pollination. 9. Wastage is little. A lot of wastage occurs in cross pollination.10. It introduces homozygosity. It maintains heterozygosity.11. It forms pure lines. It produces variations.12. It cannot introduce new traits. It can introduce new traits.13. It cannot eliminate harmful traits It can eliminate harmful traits.

unless and until they become lethal.14. It preserves highly useful traits. Highly useful traits are often diluted.15. There is fall in adaptability. It enhances adaptability to changing environment.16. Immunity to diseases falls. Immunity to diseases is maintained.17. There is decrease in yield with time. Yield seldom falls below an average minimum.

��/�� '��Pollen grains of a number of plants descend over the stigma of a flower. All of them do not germinate

there. Only the compatible pollen of the same species are able to germinate. Germination is connected withcompatibility-incompatibility reaction between proteins present over the pollen grains and the stigma. Ifthe reaction is favourable, the pollen grains pick up water and nutrients from the stigma. It results in growthof pollen grains to form pollen tubes. In the style the pollen tube grows chemotropically and after enteringovary by obturator tissue. It is futher attracted to ovule and passes into it due to chemicals released byfiliform apparatus of the synergids. All the events from deposition of pollen over the stigma to the entry ofpollen tube in the ovule are together called pollen-pistil interaction.

In the absence of compatibility–incompatibility reaction, pollen grains will germinate invariably,provided water and nutrients are available. Place a drop of 10% sugar solution over a slide. Sprinkle pollengrains of 3–5 species (e.g., Vinca, Balsam, Crotalaria, Chick Pea, Pea) over it. Observe after 15-30minutes. You will be able to find pollen tubes coming out of the pollen grains. Therefore, understanding themechanism of compatibility-incompatibility between the pollen and the pistil is important. It can helpovercome incompatible reactions by supplying the chemicals that induce compatibility and allow the pollento grow. Plant breeders will then be able to obtain hybrids between different species.

��0! ��+��It is technique in plant breeding where crosses are made between different varieties, species and even

genera in order to combine their desirable characters in a single superior variety. Artificial hybridization isone of the major approaches in crop improvement. In this technique, it is important that only desired pollengrains are used in pollination and the stigma of the desired plant is protected from contamination fromunwanted pollen. This is carried out by the two processes of emasculation and bagging.

Emasculation is the practice of removing anthers in their bud condition from the bisexual flowers ofplants selected as female parents by means of a pair of fine forceps. Bagging is the covering of bothemasculated and nonemasculated flowers with butter paper or polythene in their bud condition to preventcontamination from unwanted pollen. When the stigmas of emasculated flowers mature, the bags areremoved for a while. The stigmas are dusted with pollen grains of desired male plants by means of a brush.The flowers are rebagged till fruits develop. Emasculation is not required in case of unisexual flowers.However, flowers are bagged to prevent contamination.

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��+�� It is the process of syngamy or fusion of compatible male and female gametes. In seed plants,

fertilization is also called siphonogamy as it is accomplished by pollen tube which brings male gamete incontact with female gamete. Siphonogamy was discovered by Strasburger (1884).

Germination of Pollen Grain onStigma. A large number of pollen grainsfall on the stigma. It sets in pollen-pistilinteraction. Only the compatable pollengrains germinate and grow. They absorbnourishment and swell up. The swollen tubecell grows out of the pollen grain throughone of the germ pores. It produces a pollentube. Pollen tube is covered by intine only.Generative cell divides into two malegametes, if it has not divided already.

Path taken up by Pollen Tube. Pollentube contains two male gametes, adegenerating tube nucleus and somecytoplasm. It secretes pectinases and otherhydrolysing enzymes to create anintercellular pathway for it through thestigma. It passes through the style along itscanal or conducting (transmitting) tissue incase of solid style. Advancing pollen tubeobtains nourishment from special cells (e.g.,transmitting or conducting tissue) in thestyle. Passage of pollen tube in the stigma

and style is determined chemotropically along the increasing concentration of calcium-boron-inositol sugarcomplex as well as copper containing chemocyanin. In the ovary, pollen tube is guided and nourished byanother tissue called obturator. Ultimately, a pollen tube reaches an ovule and enters it. Passage of pollentube into ovule can occur by any of the following three ways :

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�Fig. 2.25. Entry of male gametes into embryo sac.

�Fig. 2.24. Fertilization in an angiosperm through porogamy.

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24 ��#�%�� #��, #)#&-�.��(i) Porogamy. Entry of pollen tube into ovule through the micropyle. It is the most common way in

angiosperms, e.g., Lily.(ii) Chalozogamy. Entry of pollen tube into ovule through chalaza, e.g., Betula, Casuarina, Juglans

(Walnut).(iii) Mesogamy. Entry of pollen tube into ovule through integuments (Cucurbita, Populus) and funiculus

(e.g., Pistacia).

Entry of Pollen Tube into Embryo Sac. After entering the ovule, the pollen tube is attracted to themicropylar end of embyo sac by the secretion of synergids. It strikes and enters one of the two synergids.

A subterminal pore appears in the pollen tube. Pollentube contents come out of it. Both the male gametesor sperm cells are functional in flowering plants.They perform generative fertilization and vegetativefertilization.

(a) Generative Fertilization (Syngamy). It isfusion of one of the two male gametes with egg toproduce a diploid zygote (oospore). Generativefertilization or syngamy is also called truefertilization. Plasmodesmal connections of fertilizedegg degenerate. The oospore now begins to grow andform embryo.

(b) Vegetative Fertilization. It is the fusion ofsecond male gamete with two haploid polar nuclei ordiploid secondary nucleus of central cell to formtriploid primary endosperm nucleus or PEN. It isalso called triple fusion, as there is fusion of threenuclei. Triple fusion changes central cell into primaryendosperm cell or PEC. The latter gives rise tonutritive tissue called endosperm.

Double Fertilization. It is fusion of two male gametes brought by a pollen tube with two differentstructures (i.e., egg and diploid secondary nucleus) in the same female gametophyte to produce two differentstructures (zygote and primary endosperm cell). Double fertilization was discovered by Nawaschin, 1898 inFritillaria and Lilium. It was confirmed by Guignard (1899). Double fertilization is restricted to angiosperms.It is, however, absent in some families (e.g., Trapaceae, Podostemonaceae, Orchidaceae). The two componentsof double fertilization are generative fertilization and vegetative fertilization. In generative fertilizationone male gamete fuses with oosphere to form zygote that later gives rise to embryo. In vegetativefertilization, a male gamete fuses with diploid secondary nucleus or two haploid polar nuclei in triplefusion to form primary endosperm nucleus (PEN) while the central cell of embryo sac is changed intoprimary endosperm cell (PEC). Later on, it gives rise to endosperm.

Significance of Double Fertilization. (i) It provides characteristics of the male parent to endospermwhich are useful in storage of nutrients. (ii) It ensures formation of endosperm only when the egg has beenfertilised and embryo development is to start. (iii) Vegetative fertilization or triple fusion provides astimulus akin to hybrid vigour for growth and formation of endosperm by aggressive withdrawal ofnourishment from nucellus and parent plant.��*��:��

Flowers begin to fade after fertilization. Sepals, petals, stamens and style wither away and are shed.During this period there is spurt in ethylene production accompanied by increase in respiration. In manyflowers, sepals are not shed. They are called persistent sepals, e.g., Solanum, Petunia, Lycopersicum. InPhysalis, Dillenia and a few others, sepals grow with the growth of fruit. They are called accrescent sepals.Major post fertilization events include endosperm formation, embryo formation, maturation of ovule intoseed and ovary into fruit.

�Fig. 2.26. Fertilized embryo sac.

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Table 2.1. Post Fertilization Changes in Floral Parts

1. Sepals. Fall down, Persist in a few 9. Inner Integument. Tegmen (if present)2. Petals. Fall down 10. Micropyle. Micropyle3. Stamens. Fall down 11. Nucellus. Consumed. Perisperm if present4. Stigma, Style. Fall down 12. Oosphere. Zygote � Embryo5. Ovary. Fruit 13. Synergids. Degenerate6. Ovary Wall. Pericarp 14. Antipodal Cells. Degenerate7. Ovules. Seeds 15. Central Cell. Endosperm. May persist or get consumed.

8. Outer Integument. Testa

��1�2�� &��Endosperm is a special nutritive tissue. Its development precedes the development of embryo as it is to

nourish the same. It is gametophytic in gymnosperms and post-fertilization product in flowering plants. Inflowering plants, endosperm is generally triploid as it is formed from the product of triple fusion or fusion ofone male gamete with two polar nuclei (or diploid secondary nucleus). For its formation, endosperm obtainsfood from nucellus, endothelium and the parent plant. As a result, nucellus and endothelium degenerate. Onthe basis of its formation, endosperm is of three types—nuclear, cellular and helobial.

1. Nuclear Endosperm. It is the common type of endosperm. It develops in two phases, coenocytic andcellularisation. (i) Coenocytic Phase. Primary endosperm nucleus or PEN divides and redivides to form alarge number of free nuclei. It gives rise to a multinucleate endosperm. A central vacuole developstemporarily for quickening the growth of endosperm. (ii) Cellularisation Phase. Wall formation or cytokinesisbegins from periphery and proceeds towards the centre. It makes the endosperm a multicellular tissue, e.g.,Maize, Wheat, Rice, Sunflower, Capsella. Number of free nuclei formed prior to cellularisation variesgreatly. Cytokinesis may also stop prematurely. Coconut has white kernel of solid multicellular endospermon the outside and ‘‘milky’’ free nuclear liquid endosperm in the centre made of thousands of free nuclei.Tender coconut is highly nutritious as its milk is rich in vitamins, minerals, sugars, proteins and with littlesaturated fats. In Crotalaria cytokinesis is restricted to upper half while in Phaseolus it occurs in areaaround the embryo.

2. Cellular Endosperm. Cytokinesis occurs after every nuclear division so that endosperm is ofcellular form from the beginning e.g., Datura, Petunia, Impatiens, Magnolia.

3. Helobial Endosperm. First division of primary endosperm nucleus is followed by cytokinesis toproduce two unequal chambers, larger micropylar and smaller chalazal. Subsequent divisions are freenuclear in both the chambers. They are rapid in microphylar chamber. The chalazal chamber may degenerateor continue slow growth. In the latter case both the chambers ultimately become cellular, e.g., Asphodelus,Eremurus.

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�Fig. 2.27. Types of Endosperm.

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Fate of Endosperm. Endosperm is meant for nourishing the embryo. In many dicots, the food reservepresent in endosperm is completely consumed by the growing embryo so that in the seed the remains ofendosperm are hardly discernible. Such seeds are called non-endospermic or exalbuminous. Reserve foodfor future development of embryo into seedling is kept in either nucellus or cotyledons, e.g., Pea, Bean,Sunflower. In cereals, Coconut and many other plants, the endosperm enlarges and retains the reserve foodin the mature seeds. Such seeds are called endospermic or albuminous. Endosperm is quite hard inPhoenix (Date), Areca (Betal Nut) and Phytelepas (Vegetable Ivory). It is convoluted or ruminate in case ofAreca and Passiflora.

��1��&� �!��&� �!��!Embryo is the young future offspring which in seed plants develops inside mature fertilized ovule or

seed. It is formed from zygote. Formation of embryo from zygote is called embryogeny. It begins at themicropylar end of embryosac only when a certain amount of endosperm has been formed. This assuresproper food supply to the developing embryo. Early embryo development is similar in both dicots andmonocots. Embryo development is meroblastic (from a part of zygote) and endoscopic (towards interior dueto presence of suspensor). Early embryo has an axial symmetry and is called proembryo. Proembryo passesthrough globular form to heart shaped and then mature stages of embryo.

1. Dicot Embryogeny (Crucifer/Onagrad Type). Zygote completes the wall over the chalazal region.Plasmodesmal connections degenerate. The freed zygote elongates and becomes polarised. The basal parthas a large central vacuole while the terminal part contains dense cytoplasm. An unequal transversedivision produces a larger basal cell and a smaller terminal (apical) cell.

(i) Basal Cell. It is larger cell of two celled derivative of zygote which occurs towards the micropylarend. Basal cell enlarges further and undergoes transverse divisions to produce 6-10 celled filament calledsuspensor. Because of the formation of suspensor, the basal cell is also called suspensor cell. The first cellof suspensor that lies towards the micropyle is often quite large and vacuolate. It is called haustorium.Suspensor is meant for pushing the young embryo into food laden endosperm. The last cell of suspensor incontact with proembroyo is called hypophysis. It later on gives rise to part of root cap and radicle.

(ii) Terminal or Apical Cell. It is the smaller cell of two-celled derivative of zygote which liestowards the chalazal or antipodal end. Terminal cell is also called embryo cell as it is to form the majorparts of embryo. It undergoes one transverse and two vertical divisions to produce 2-tiered and 8-celledproembryo. The tier towards the suspensor forms hypocotyl and part of radicle. A root cap develops overthe radicle or root tip. The other apical tier gives rise to plumule, epicotyl and two cotyledons. The twoembryo tiers undergo periclinal divisions forming outer dermatogen (or protoderm), middle ground meristermand central procambium. Cotyledons grow very fast while plumule forms a small mound of meristematictissue in between the two cotyledons. With the growth of cotyledons, the embryo becomes heart-shaped andthen assumes the typical shape.

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�Fig. 2.28. Development of dicot embryo.

2. Monocot Embryogeny (Sagittaria Type). The fertilized egg completes wall towards the antipodal orchalazal side, breaks plasmodesmal connections and divides into two unequal cells, basal cell and terminalcell. The basal cell occurs towards the micropylar end. Generally it forms a vesicular suspensor cell. A fewcells are often added to suspensor by the terminal cell. The terminal cell undergoes divisions to produce twotiered embryo. The tier towards the suspensor forms radicle and root cap. The other tier produces a cotyledonand plumule. Growth of cotyledon is massive. It pushes the plumule to one side. The single cotyledon is calledscutellum. Remains of second cotyledon may be found in the form of epiblast in some grasses. Hypocotyl andepicotyl are short. Epicotyl ends in plumule having shoot apex and a few leaf primordia. Extensions ofscutellum form coverings, coleorhiza (around radicle and root cap) and coleoptile (around plumule).

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�Fig. 2.29. Embryonic Development in Monocotyledons (e.g., Grass).

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Endosperm

1. It is nutritive tissue that develops from femalegametophyte or a part of it.

2. Endosperm is triploid in angiosperms and haploid ingymnosperms.

3. It is fleshy in nature which becomes dry in mature

seed.

Example : Castor, Maize.

Testa

It is covering of the seed called seed coat.Testa consists of highly thick-walled cells.The cells are dead.Testa is quite thick.Testa is formed from integument through growth,division, thickening and death of cells.Testa is protective structure which helps the seed inpassing through dry, cold and hot environment.

Exalbuminous/Nonendospermic Seed

An endosperm is absent.

The food is stored in the cotyledons or some othertissue but not in endosperm.

The cotyledons are often thick.

Example. Bean.

��1�3��Seed is the final product of sexual reproduction. It is often called ripened ovule. The fruit is similarly

called ripened ovary. Seeds develop inside fruit. A typical seed consists of 1-2 seed coats, 1-2 cotyledons andan embryo axis. Stored food for later development of embryo is present either in cotyledons or endosperm.Where food is present in cotyledons, the latter are thick. Such seeds are called exalbuminous or non-endospermic, e.g. Pea, Gram, Bean, Groundnut. In exalbuminous seeds, the endosperm is consumed duringgrowth of the embryo and transfer of food to cotyledons. In albuminous or endospermic seeds, the whole ofendosperm is not consumed during development of embryo. Sufficient food is also kept stored in it for futuredevelopment of embryo, e.g., Wheat, Maize, Barley, Castor, Onion, Sunflower. Remnants of nucellus persistin some seeds. The residual, persistent nucellus is called perisperm, e.g., Black Pepper, Beet, Water lily.

Differences Between Albuminous and Exalbuminous Seeds

S. No. Albuminous/Endospermic Seed

1. The seed contains a special tissue called endosperm.

2. The food is stored in endosperm.

3. The cotyledons are thin.

Example. Castor, Maize.

With the growth of embryo and endosperm, the integuments enlarge. The outer integument becomesseveral cells in thickness. Later on thickenings develop in its cells. The cells also become empty and dead.This transforms outer integument into testa or outer seed coat. The inner integument, if present, maturesinto tegmen.

Differences Between Integument and Testa

S. No. Integument

1. It is covering of the ovule.2. Integument consists of thin-walled cells.3. The cells are living.4. Integument is thin.5. It is the original structure.

6. It has no role in perennation.

Micropyle present in the ovule persists in the seed as a small pore in the seed coat. It is meant for passageof oxygen and water in germinating seeds. With maturation of seed, metabolic activities of embryo slow down.Growth inhibitors develop. Moisture content of seed falls down and reaches 10-15%. Funiculus abscises. Hilumappears as a scar over the surface of the seed. The embryo enters a state of inactivity or dormancy. The seedwith dormant embryo can perennate through unfavourable season. It can germinate immediately afterwardsif favourable conditions (adequate moisture, oxygen and suitable temperature) are available.

Differences Between Perisperm and Endosperm

S. No. Perisperm

1. It is persistent nucellus.

2. Perisperm is diploid.

3. It is often papery.

Example : Black Pepper, Beet.

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Parthenocarpic Fruit

The fruit is devoid of seeds.

The fruit develops without fertilization.

It may or may not have additional parts.

Example. Banana.

False Fruit

Alongwith ovary some additional component ofthe flower or inflorescence grows to become thepart of the fruit.

Commonly the outer part of the fruit is formedby the thalamus.

Example. Apple.

Stimuli from pollination and growing seeds induce the ovary to grow many times its original size andform fruit. Wall of the ovary gives rise to the wall of the fruit, called pericarp. The mature pericarp maybe fleshy or dry. Accordingly, there are two types of fruits, fleshy (e.g. Guava, Orange, Mango) and dry(e.g., Groundnut, Mustard). In some cases, thalamus grows alongwith ovary wall to form part of the fruit.Such fruit are called false fruits, e.g., Apple, Strawberry, Cashewnut. In Strawberry, the actual fruits orachenes are embedded on the surface of fleshy thalamus. In Apple, the fleshy thalamus surrounds thepericarp (epicarp + mesocarp and endocarp) and centrally placed seeds. In Cashewnut, the enlargedthalamus forms the fleshy base of the fruit. No part of the flower, other than ovary, contributes to fruitformation in true fruits, e.g., Tomato, Grape. In a few species, fruits do not bear seeds. They developwithout fertilization. Such fruits are called parthenocarpic fruits, e.g., Banana. Parthenocarpy or formationof seedless fruits can also be induced by growth hormones. However, it is of no use to the plant. Seedsensure the continuity of the race and perennation during unfavourable seasons. Some fruits bear a very largenumber of tiny seeds for easy dispersal through wind and birds, e.g., Orchids, Orobanche, Striga, Ficus.

Differences Between True Fruit and False Fruit

S. No. True Fruit

1. The fruit develops from only the ovary part

of the flower.

2. Pericarp forms the outer part of the fruit.

Example. Tomato.

Differences Between False Fruit and Parthenocarpic Fruits

S. No. False Fruit

1. The fruit contains seeds.

2. Fertilization is essential for its development.

3. Additional parts of flower or inflorescence

grow alongwith growth of the fruit.

Example. Apple.

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�Fig. 2.30. False fruits. A, Apple B, Strawberry.

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Hypocotyl

It is area of embryo axis between radicle andcotyledonary node.

In epigeal germination, hypocotyl elongates to push theseed with contained plumule and cotyledons, above thesoil.

It is a component of embryonic root system.

Differences Between Perisperm and Pericarp

S. No. Perisperm

1. It is part of seed.

2. Perisperm represents remains of nucellus.

3. It is usually dry.

4. Perisperm has little functional importance.

5. It has a shrivelled appearance.

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1. Bean Seed. It is dicotyledonous, non-endospermic seed. The seed is kidney-shaped in outline. Colouris brown. Concave side is darker with a whitish scar or hilum. A micropyle occurs at one end of hilum.Raphe lies on the opposite side. Bulge indicating position of underlying radicle lies close to hilum. The seedis covered by a thick tough seed coat called testa. A thin inner transparent tegmen is also discernible.Embryo has a curved axis or tigellum. Two large thick cotyledons arise from the middle of embryo axiswhere a cotyledonary node is present. The cotyledons have become large and thick due to storage of food.One end of embryo axis (lying in between the cotyledons) is plumule (or future shoot). It has two smallfolded leaves. Part of embryo axis between the cotyledonary node and plumule is called epicotyl. The otherend of embryo axis (which protrudes partially from cotyledons is radicle (or future root). Part of axisbetween radicle and cotyledonary node is called hypocotyl.

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�Fig. 2.31. Bean seed. A, lateral view. B, ventral view. C, seed cut open.

Differences Between Epicotyl and Hypocotyl

S. No. Epicotyl

1. It is area of embryo axis between plumule andcotyledonary node.

2. In hypogeal germination epicotyl elongates to pushthe plumule above the soil. The seed remainsunderground.

3. It is a component of embryonic shoot system.

2. Castor Seed. It is a dicotyledonous endospermic seed. The seed is oblong in outline with mottledbrown shining surface, a flat ventral side, convex dorsal side, narrow proximal end and a broad distal end.The proximal narrow end bears a bilobed white spongy caruncle. It helps in bulk absorption of water duringgermination of the seed. Hilum and micropyle lie ventrally below the caruncle. Raphe runs ventrally fromhilum. The seed is covered by a thick hard but brittle testa. A thin tegmen (considered perisperm by some)lies below it. Endosperm is oily food storing tissue that lies between seed coats and embryo. Embryo lies

Pericarp

It is part of fruit.

It represents growth of ovarian wall.

It can be dry or fleshy.

Pericarp takes part in protection, dispersal and nutrition.

There is no shrivelling whether the pericarp is dry or

fleshy.

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centrally. It has a short embryo axis or tigellum, two large papery palmately veined whitish cotyledons, aknob-like radicle and a very small plumule. In germinating castor seed, the cotyledons turn green and formthe first leaves of the seedling.

�Fig. 2.32. Castor seed. A, external view. B, L.S. parallel to flat surface. C, L.S. at rightangles to flat surface.

3. Maize Grain. It is monocotyledonous endospermic, single-seeded fruit called caryopsis. The grain isflat and conical in outline with whitish to reddish-violet colour. The proximal narrow end has small loosehusk. Distal broader rounded end bears a conical papilla on the flat surface. It represents remains of style.Hilum and micropyle are absent (as the grain is a fruit and not a seed). A deltoid light coloured depressionoccurs on the flat surface. It indicates the position of underlying embryo. The outer hard covering of thegrain consists of fused testa (seed coat) and pericarp (fruit wall). Most of the grain interior on the broaderand lower sides contains endosperm while 1/3 area of grain (on upper and pointed sides) contains embryo.Endosperm has protein rich outer thick walled aleurone layer while the remaining starch rich part is calledstorage region. Embryo consists of an embryo axis and a large lateral single cotyledon called scutellum.End of embryo axis towards broader side has plumule with a few rudimentary leaves. End of the embryoaxis towards the pointed end is radicle covered with root cap. Special coverings, considered to beextensions of scutellum, are present over plumule and radicle-root cap. They are called coleoptile andcoleorhiza respectively. Coleoptile pierces the grain covering, turns green and comes out of the soil. Theepicotyl grows simultaneously and brings the plumule above the soil, protected inside the coleoptile.Coleorhiza is meant for piercing the grain covering to pave way for growth of radicle. It also forms a fewsmall roots called seminal roots. Surface of scutellum in contact with endosperm is called epithelial layer.It produces hormones (e.g., gibberellins) for development of enzymes from aleurone layer in order tomobilise food reserve of endosperm at the time of seed germination.

�Fig. 2.33. Grain of Maize. A, external view. B, L.S. grain.

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Differences Between Coleoptile and Coleorhiza

S. No. Coleoptile

1. It is covering of plumule in monocot grains.

2. Coleoptile pierces grain covering and elongates.

3. Coleoptile comes out of soil.

4. It turns green.

5. It protects the plumule during its emergence

from soil.

6. It is component of embryonal shoot.

4. Onion Seed. It is a monocotyledonousendospermic seed. The seed is small, black and

wrinkled. A tough seed coat is present on the outside.Internally there is a tough semitransparent endosperm.A curved embryo lies inside the endosperm. Embryo

has a large cotyledon or scutellum which isdifferentiated from the embryo axis by a notch. Radiclelies on the other side. Hypocotyl is present. Plumule

is, however, not differentiable. Instead shoot apicalmeristem is present close to the notch from wherethe cotyledon grows. Plumule develops later.

Differences Between Dicot and Monocot Seeds

S. No. Dicot Seed/Bean Seed Monocot Seed/Maize/Onion Seed

1. The seed possesses two cotyledons. The seed possesses a single cotyledon.

2. Plumule is terminal. Plumule appears lateral.

3. Plumule lies in between the two cotyledons. Plumule lies on one side of the large cotyledon.

4. The seed may be endospermic or non- The seed is generally endospermic.endospermic.

5. Special coverings do not occur over plumule In many cases the radicle and plumule are

and radicle. surrounded by special coverings like coleorhiza

and coleoptile.

Coleorhiza

It is covering of radicle-root cap complex in monocotgrains.

It pierces grain covering but stops further growth.

It remains inside soil.

Coleorhiza does not develop green colour.

It has no such role.

It is component of embryonal root.

�Fig. 2.34. L.S. Seed of Onion.

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To Plants

1. Dependable Process. Seed formation is connected with pollination and fertilization that are independentof water. It is, therefore, more dependable process.

2. Evolutionary Achievement. Seed is an evolutionary achievement. It provides protection to embryowhich is the most delicate stage in the life history of plants.

3. Perennation. Seed enables the future plant to pass through unfavourable periods without any harmbecause of the (i) Presence of tough covering. (ii) Dormant embryo. (iii) Dehydrated protoplasm.(iv) Inactive enzymes. With the arrival of next favourable season, the seeds germinate and form new plants.

��/'�)��%"#('!� #�� )#0�" �&��)��$ 334. Dispersal. Seeds have adaptive strategies for dispersal to new habitats through the agencies of wind,

water and animals. This helps in spread of species and colonisation of new areas.

5. Food Reserve. Seed has sufficient food reserve that nourishes the germinating embryo and growingseedling till it becomes photosynthetically independent.

6. Variations. Being products of sexual reproduction, seeds have a number of variations due to geneticrecombinations and crossing over. The variations are helpful in adaptations to varied environments andstruggle for existence.

7. Perpetuation. Seeds are a means of multiplication of higher plants. Being capable of perennation,seeds help in perpetuation of plants even in case of drought and famine for a few successive years.

To Mankind

8. Food. Seeds are a major article of human diet. They are also a source of oils, fibres, spices,beverages, etc. The major benefit of seeds is that they can be stored for a few years. Stored seeds functionas an insurance against drought and vagaries of nature.

9. Agriculture. Discovery of edible nature of some seeds, their germination and sowing by earlyhumans gave rise to agriculture. Agriculture liberated the early humans from the drudgery of gatheringfood. It helped in development of civilisation, progressive improvement in knowledge, development ofscience and technology.

�� !It is the period of time for which the seeds retain the ability to germinate. Seed viability is determined

genetically as well as environmentally. Environmental conditions which can alter viability are humidity andtemperature. Genetically seed viability ranges from a few days (e.g., Oxalis), one season (e.g., Birch), 2-5years (most crop plants) to 100 years (e.g., Trifolium).

Seed viability has been found out to be more than 1000 years in Lotus. 2000 years old seeds of Phoenixdactylifera excavated from King Herod's palace near Dead Sea have been found viable. Similarly, 10000 yearsold seeds of Lupinus arcticus (Lupine) excavated from Arctic Tundra not only germinated but also produced plantsthat flowered. Viability of a seed is tested by its (a) respiration (b) germination. A respiring seed turns colourlesstriphenyl tetrazolium chloride into pink triphenyl formazan.

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Apomixis (Gk. apo—without, mixis—marriage; Winkler, 1908) is the formation of new individuals byasexual methods which mimic sexual reproduction including seed formation but do not involve fusion ofgametes or sex cells. The organism reproducing through apomixis is called apomict. Apomixis is controlledby genes. In apomixis the new individuals are genetically similar to the parent producing them. They are,therefore, clone of their parent. Members of a clone are called ramets. Apomixis can be recurrent ornonrecurrent. It occurs by the following methods :

(i) Agamospermy (Gk. agamos—without marriage, sperma—seed). It is mode of apomixis in which seedsare formed but are asexual in nature as the embryo develops directly without gametic fusion. It is commonlyformed from a diploid nucellar cell (apospory) or megaspore mother cell (diplospory). The term apospory isalso used for development of embryo sac or gametophyte directly from sporophytic tissue.

The term sporophytic budding is used if the embryo develops adventitiously from diploid cells ofnucellus or integument, e.g., Mango, Orange, Opuntia, Onion. The embryo is pushed into the area ofembryo sac to replace the normal embryo.

(ii) Parthenogenesis (Gk. parthenos—virgin, genesis—descent; Owen, 1848). It is the development of a

new individual from a single gamete without fusion with another gamete. In lower plants both the types of

gametes can undergo parthenogenesis but in higher plants, usually the female gamete shows this faculty.

Depending upon the ploidy of the gamete, there are two types of parthenogenesis, diploid and haploid. In

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Such embryos do not survive in higher plants but in lower plants, the plant body is haploid so that haploid

embryo has survival value. In diploid parthenogenesis, the embryo sac as well as its contained egg is

diploid. It undergoes parthenogenesis and forms diploid embryo. Diploid parthenogenesis is generally

accompanied by failure of meiosis during megasporogenesis as well as direct formation of embryo sac from

a nucellar cell, e.g., Rubus, Poa, Apple. In Apple, self pollination promotes diploid parthenogenesis

(Campbell and Wilson, 1962).

(iii) Apogamy (Gk. apo—without, gamos—marriage). It is formation of sporophyte or embryo directly

from cells of gametophyte. In higher plants, only diploid apogamy is successful, that is, the gametophytic

cell forming the sporophyte is diploid. In lower plants, haploid apogamy is equally successful.

Polyembryony is the phenomenon of

formation of more than one embryo during

the development of seed. While polyembryony

generally occurs during seed development, Rao

(1965) has found polyembryony to develop

during seed germination in Vanda caused by

cleavage of apical promeristem of single

embryo. Polyembryony was discovered by

Leeuwenhoek (1719) in case of Citrus.

Polyembryony is of three types—simple,cleavage and adventitive.

(i) Simple Polyembryony. It is due tofertilization of more than one egg cell in anovule. The condition develops when an embryosac contains more than one egg cell or theovule possesses more than one embryo sac,e.g., Casuarina, Citrus, Poa.

(ii) Cleavage Polyembryony. Polyembryony iscaused by splitting of proembryo into two or more parts and branching of proembryo. Another reason ofcleavage is the splitting of suspensor. It is common in conifers (e.g., Pinus). Amongst angiosperms cleavagepolyembryony is recorded in orchids.

(iii) Adventitive Polyembryony. It is formation of additional embryos from different parts of ovule(other than egg of the embryo sac) like synergids, antipodal cells, nucellus, integuments, etc. (e.g., Citrus,

Opuntia, Mangifera, Trillium, Onion, Groundnut).

Differences Between Apomixis and Polyembryony

S.No. Apomixis Polyembryony

1. It is the formation of new individual by asexual It is the formation of more than one embryo during

method. the development of seed.

2. It occurs through agamospermy, parthenogenesis It occurs due to fertilization of more than one

and apogamy. oosphere, cleavage and adventitive budding.

��!�� !�!1. Adventitive embryos are fully viable.2. Apomictic embryos are free from infection.

�Fig. 2.35. Polyembryony in Citrus.

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Parthenocarpy

It is the formation of a seedless fruit.

It has no role in reproduction.

Apomixis

It produces a fruit containing seed.

It takes part in reproduction.

It is agriculturally important.

Ex. Occasional in Mango, Apple.

3. Adventitive embryos are true clones of their parents.

4. The phenomenon can be used to maintain hybrid varieties indefinitely. Hybrid varieties are preferredby agriculturists because of their higher yield, vigour and resistance to stresses. They have tremendouslyincreased crop productivity, e.g. Maize, Tomato, Cauliflower, Sorghum, Pearl Millet. However, there is onemajor defect in using hybrid varieties. Hybrid vigour is not maintained beyond single generation as segregationof genes begins to occur in second generation. In order to maintain higher yield, hybrid seeds have to bedeveloped every year. It is costly. Hybrid seeds are, therefore, quite expensive to the farmers. Therefore,agriculture scientists are searching for the methods to maintain hybrid traits indefinitely. One of the possiblemethods is the development of seeds through apomixis. Since the embryo in apomictic seeds often develops fromdiploid cells, segregation of traits will not occur and the new seeds will contain all the traits of the hybridvariety. Apomixis is controlled genetically. Genes controlling apomixis are being searched. As soon as theyare located, efforts will be made to transfer them into hybrid varieties.

�� !(Gk. parthenos—virgin, karpos— fruit, Noll, 1902).

It is the formation of fruit without fertilization (Nitsch, 1965). In some cases the stimulus of pollinationis required. The phenomenon is called stimulative parthenocarpy. In others parthenocarpy occurs inunpollinated flowers. It is vegetative parthenocarpy. Parthenocarpic fruits are generally seedless. However,technically fruits having seeds (pseudoseeds) with an asexual embryo are also parthenocarpic fruits.Parthenocarpy is of three types—genetic, environmental and chemically induced.

(i) Genetic Parthenocarpy. Parthenocarpy is due to genetic alteration caused by mutation or hybridisation.It is also called natural parthenocarpy, e.g., Navel Orange, Banana, Pineapple, varieties of Apple, Grapeand Pear.

(ii) Environmental Parthenocarpy. Low temperature, frost and fog have been known to induceparthenocarpy in a number of plants, e.g., Pear, Olive, Capsicum, Tomato.

(iii) Chemically Induced Parthenocarpy. Spray or paste of auxins and gibberellins in low concentrationof 10-6—10-7 M has been found to induce parthenocarphy in several plants, e.g., Tomato, Vitis, Cucurbits,Citrus, Strawberry, Blackberry, Fig, etc.

Differences Between Parthenocarpy and Apomixis

S.No. Parthenocarpy

1. It is formation of seedless fruit.

2. Parthenocarpy has no role in reproduction.

3. It is economically important.

Ex. Banana.

Formation of seedless parthenocarpic fruits is economically important as (i) They do not containirritant seeds which have to be removed before eating the fruits. (ii) Development of fruit plants insidegreen houses where natural pollinators are generally not available. (iii) Quicker food processing. However,parthenocarpy has no biological importance to the plants and is useless in fruits where seeds or seed partsare economically important, e.g., Pomegranate.

Differences Between Parthenogenesis and Parthenocarpy

S.No. Parthenogenesis

1. It is development of an embryo or new individual

from a single gamete without the process of

fertilization.

2. It can take part in reproduction.

46 ��#�%�� #��, #)#&-�.��

Polyembryony

It occurs in seeds.

It has more than one embryo.

Reproduction occurs through seeds.

It is produced through fertilization of more than

one egg, cleavage and adventive budding.

Parthenocarpy has no biological significance. It is,

however, economically important.

It does not produce new plants.

3. Parthenogenesis is biologically important as a single

gamete takes part in reproduction in the absence

of a second gamete.

4. It produces new plants which can be haploid or

diploid.

Differences Between Parthenocarpy and Polyembryony

S.No. Parthenocarpy

1. It occurs in seedless fruits.

2. An embryo is absent.

3. Reproduction occurs through asexual methods.

4. It is hormone induced development of ovary and

other parts.

Significance of Seed and Fruit Formation

Seed is an evolutionary development in which the future plant is packed in a dormant state withadequate food and protective covering. The device is useful to land plants for perennation during unfavourableperiod and production of new plants on favourable substratum in favourable season. For this there is amechanism for passage of air and water to the seeds when the latter are available.

Formation of fruit has provided added advantage to angiosperms (i) Fruit protects the seeds in theirdelicate developmental stage (ii) Many fruits help the seeds in their dispersal (iii) Seed germination isfacilitated by remains of the fruit. (iv) Fleshy edible parts of fruits are a source of food and energy to manyanimals. For this, soft fleshy pericarp encloses hard seeds (e.g., Guava). The opposite is also true, that is,soft seeds are enclosed by hard shell (e.g., Almond). (v) Fruits are a source of many chemicals like sugars,oil, protein, organic acids, vitamins and minerals.

Significance of Seed Dispersal

The scattering of seeds away from the parent plant is called seed dispersal. It occurs through forcefulbursting of fruits (autochory), wind (anemochory), water (hydrochory) and animals (zoochory). Seed dispersalis a must for plants because (i) Plants are fixed. All the seeds formed by them cannot germinate belowthem. They must be sent away. (ii) It helps in spreading the plants far and wide throughout the area offavourable climate. (iii) Dispersal forms a mixed population where competition for the same resources isless. (iv) Dispersed plants have higher chances of cross pollination. (v) It provides protection againstdrought, epidemic spread of a disease and pest in an area.

1. Define parthenocarpy. (C.B.S.E. 2007)

2. Mention the scientific term used for modified form of reproduction in which seeds are formedwithout fusion of gametes. (C.B.S.E. 2007)

3. Mention one application of pollen bank. How are pollens stored in a bank ?

(C.B.S.E. 2008 Comptt.)

4. The microscopic pollen grains of the past are obtained as fossils. Mention the characteristics of thepollen grains that makes it happen. (C.B.S.E. 2009)

5. Mention the pollinating agent of an inflorescence of small dull coloured flowers with well exposedstamens and large feathery stigma. Give any one characteristic of pollen grains produced by suchflowers. (C.B.S.E. 2009)

��/'�)��%"#('!� #�� )#0�" �&��)��$ 4�6. Name the type of flower which favours cross pollination. (C.B.S.E. 2009)

7. The meiocyte of Rice has 24 chromosomes. How many chromosomes are present in itsendosperm ? (C.B.S.E. 2009)

8. Which of the following is an incorrect about water pollinated submerged plants. (i) The flowers donot produce nectar. (ii) The pollen grains have mucilaginous covering. (iii) The brightly colouredfemale flowers have long stalks to reach the surface. (C.B.S.E. 2009)

9. Name the type of pollination as a result of which genetically different types of pollen grains of thesame species land on the stigma. (C.B.S.E. 2009)

10. Name the part of flower that contributes to fruit formation in Strawberry and Guava respectively.

(C.B.S.E. 2009 Comptt.)

11. Why are non-albuminous seeds so called ? (C.B.S.E. 2009 Comptt.)

12. A bilobed, dithecous anther has 100 microspore mother cells per microsporangium. How manymale gametophytes this anther can produce ? (C.B.S.E. 2010)

13. An anther with malfunctioning tapetum often fails to produce viable male gametophytes. Give onereason. (C.B.S.E. 2010)

14. Pea flowers produce assured seed sets. Give a reason. (C.B.S.E. 2010)

15. Banana is a true fruit but is also parthenocarpic fruit. Give reasons. (C.B.S.E. 2010)

16. Normally one embryo develops in one seed but when an orange seed is squeezed many embryos ofdifferent shapes and sizes are seen. Mention how it has happened ? (C.B.S.E. 2011)

17. Why is banana considered a good example of parthenocarpy ? (C.B.S.E. 2012)18. How do the pollen grains of Vallisneria protect themselves ? (C.B.S.E. 2012)19. How is it possible in Oxalis and Viola plants to produce assured seed sets even in the absence of

pollinators. (C.B.S.E. 2012)20. Papaver and Michelia have both multicarpellary ovaries. How do they differ from each other ?

(C.B.S.E. 2012)21. Banana produces fruits but is propagated only by vegetative means. Why is it so ?

(C.B.S.E. 2012)

22. Write the function of scutellum/tapetum (in anthers) (C.B.S.E. 2012)23. An anther with malfunctioning tapetum often fails to produce viable male gametophytes. Give any

one reason. (C.B.S.E. 2013)

24. Name the part of the plant which the tassels of corn cob represent. (C.B.S.E. 2014)

25. Give an example of a plant which came into India as a contaminant and the cause of pollen allergy.(C.B.S.E. 2014)

26. The diploid number of chromosomes in an angiospermic plant is 16. What will be the number ofchromosomes in its endosperm and antipodal cells ? (C.B.S.E. 2019)

27. State reason why pollen grains lose their viability when tapetum in the anther is malfunctioning.

(C.B.S.E. 2019)

28. Apospory produces .................... gametophytes.

29. Secretion of pollenkitt takes place in ...................... pollen grain.

30. Study of pollen grain is ................ .

31. In Vallisneria, pollination takes place by ................... .

32. Pollination in Cobra Plant occurs by ................ .

33. Double fertilization was first time discovered by .................. .

4� ��#�%�� #��, #)#&-�.��

34. Development of male gametophyte in angiosperms is precocious.

35. Anatropous ovule is present in members of piperaceae.

36. Vegetative fertilization in angiosperms is also called triple fusion.

37. Cellular endosperm is present in Datura.

38. Circinotropous type of ovule is present in Capsella.

39. Polyembryony was first reported by Leeuwenhoek (1719) in Citrus.

28. diploid 29. Entomophilous 30. Palynology 31. Water 32. Snail

33. Nawaschin, 1898 34. True 35. False 36. True 37. True

38. False 39. True

1. Define apomixis. Mention any two applications of apomicts in hybrid seed industry. How is itdifferent from polyembryony ? (C.B.S.E. 2008 Comptt., 2015)

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��

3. How does the floral pattern of Mediterranean orchid, Ophrys, guarantee cross pollination ?(C.B.S.E. 2010)

4. Draw a longitudinal section of a post pollinated pistil to show entry of pollen tube into a matureembryo sac. Label filiform apparatus, chalazal end, hilum, antipodals, male gametes and secondarynucleus. (C.B.S.E. 2010)

5. Where does triple fusion take place in a flowering plant ? Why is it so called ? Mention itssignificance. (C.B.S.E. 2010)

6. If you squeeze a seed of orange, you might observe many embryos of different sizes. How is itpossible ? Explain. (C.B.S.E. 2010)

7. (a) Write the characteristic features of anther, pollen and stigma of wind pollinated flowers.

(b) How do flowers reward their insect pollinators ? Explain. (C.B.S.E. 2010)

8. (a) Mention any four strategies adopted by flowering plants to prevent self pollination.

(b) Why is geitonogamy also referred to genetical autogamy ? (C.B.S.E. 2010)

9. Explain giving two reasons why pollen grains can be best measured as fossils. (C.B.S.E. 2010)

10. How many haploid cells are present in a mature female gametophyte of a flowering plant. Namethem. (C.B.S.E. 2010)

11. Differentiate between albuminous and non-albuminous seeds, giving one example each.

(C.B.S.E. 2011)

12. Draw a diagram of a male gametophyte of an angiosperm. Label any four parts. Why is sporolleninconsidered the most resistant organic material ? (C.B.S.E. 2011)

13. Differentiate between geitonogamy and xenogamy in plants. Which one between the two will lead toinbreeding depression and why ? (C.B.S.E. 2011, 2019)

14. Where is sporopollenin present in plants ? State its significance with reference to its chemical nature.

(C.B.S.E. 2012)

15. State one advantage and one disadvantage of cleistogamy. (C.B.S.E. 2012, 2019)

��/'�)��%"#('!� #�� )#0�" �&��)��$ 4+16. Explain the function each of (a) Coleorhiza (b) Germ pores. (C.B.S.E. 2012)

17. How does the study of different parts of a flower help in identifying wind as its pollinating agent ?(C.B.S.E. 2012)

18. Write the cellular contents carried by the pollen tube. How does the pollen tube gain entry into theembryo sac ? (C.B.S.E. 2012)

19. Name the product of fertilization that forms the kernel of coconut. How does the kernel differ fromcoconut water ? (C.B.S.E. 2012)

20. (a) Mention the similarity between autogamy and geitonogamy.

(b) How does geitonogamy differ from xenogamy ? (C.B.S.E. 2012)

21. Differentiate perisperm and endosperm giving one example of each. (C.B.S.E. 2012)

22. Geitonogamous flowering plants are genetically autogamous but functionally cross pollinated. Justify.(C.B.S.E. 2013)

23. (a) How does cleistogamy ensure autogamy ? (b) State one advantage and one disadvantage of cleistogamyto the plant. (C.B.S.E. 2013)

24. Explain the steps that ensure cross pollination in an autogamous flower. (C.B.S.E. 2013, 2019)

25. In angiosperms zygote is diploid but primary endosperm cell is triploid. Explain. (C.B.S.E. 2013)

26. Name all the haploid cells present in an unfertilized mature embryo sac of a flowering plant. Writethe total number of cells in it. (C.B.S.E. 2013)

27. Differentiate between the two cells enclosed in a mature male gametophyte of an angiosperm.(C.B.S.E. 2013)

28. Explain any three advantages the seeds offer to angiosperms. (C.B.S.E. 2014)

29. Name the organic materials the exine and intine of an angiospermic pollen grains are made up.Explain the role of exine. (C.B.S.E. 2014)

30. List the post-fertilization events in angiosperms. (C.B.S.E. 2014)

31. Make a list of any three outbreeding devices that flowering plants have developed and explain howthey help to encourage cross pollination. (C.B.S.E. 2014)

32. Why are angiosperm anthers called dithecous ? Discuss the structure of its microsporangium.

(C.B.S.E. 2014)

33. State what is apomixis. Comment on its significance. How can it be commercially used ?

(C.B.S.E. 2015, 2019)

34. Why are some seeds referred to as apomictic seeds ? Mention one advantage and one disadvantage toa farmer who uses them. (C.B.S.E. 2015)

(Hint. Seeds without fertilization. Advantage. Hybrid vigour maintained indefinitely. Disadvantage.No recombination, deleterious mutations may accumulate).

35. Double fertilization is reported in plants of both Castor and Groundnut. However, the mature seeds ofGroundnut are nonalbuminous and the mature seeds of Castor are albuminous. Explain the post-fertilization events that are responsible for it. (C.B.S.E. 2015)

(Hint. Endosperm is consumed by developing embryo in Groundnut. It persists in Castor as embryoconsumes only a small part of it.)

36. A nonbiology person is quite shocked to know that Apple is a false fruit, Mango is a true fruit andBanana is a seedless fruit. As a biology student how would you satisfy this person. (C.B.S.E. 2015)

(Hint. Depends upon development and place of stimulus for fruit formation. (i) Thalamus and ovaryafter fertilization in Apple. (ii) Ovary only after fertilization in Mango. (iii) Ovary without fertilizationin Banana.)

37. Describe the development of endosperm after double fertilization in an angiosperm. Why does endospermdevelopment precede that of zygote ? (C.B.S.E. 2015)

4* ��#�%�� #��, #)#&-�.��38. A single Pea plant in your kitchen garden produces pods with viable seeds but an individual Papaya

plant does not. Explain. (C.B.S.E. 2016)

(Hints. Pea flowers are bisexual and self pollinated. Papaya is unisexual. Male plant cannot producefruits. Female plant requires pollen from male plant).

39. Gynoecium of a flower may be apocarpous or syncarpous. Explain with the help of an example each.(C.B.S.E. 2016)

40. Out of many Papaya plants growing in your garden, only a few bear fruits. Give reason.

(C.B.S.E. 2016)

41. (a) Name the organic material exine of pollen grain is made up of. How is this material advantageousto pollen grains ?

(b) Still it is observed that it does not form a continuous layer around the pollen grain. Give reason.

(c) How are pollen banks useful ? (C.B.S.E. 2016)

42. (a) How does a farmer use the dormancy of seeds to his advantage ?

(b) What advantage a seed provides to a plant ? (C.B.S.E. 2016)

43. (a) How are parthenocarpic fruits produced by some plants and apomictic seeds by some others ?Explain.

(b) How do farmers prefer using apomictic seeds ? (C.B.S.E. 2016)

44. (a) Draw a labelled sketch of a mature 7-celled and 8-nucleate embryo sec.

(b) Which one of the cells in an embryo sac produces endosperm after double fertilization ?(C.B.S.E. 2016)

45. A pollen grain in angiosperm at the time of dehiscence from an anther could be 2-celled or 3-celled.Explain. How are the cells placed within the pollen grain when shed at a 2-celled stage ?

(C.B.S.E. 2017)

46. (a) Can a flowering plant in Mumbai be pollinated by the pollen grains of the same species growing inNew Delhi ? Provide explanation to your answer.

(b) Draw a diagram of a pistil where pollination has successfully occurred. Label the parts involvedin reaching the male gametes to their desired destination. (C.B.S.E. 2017, 2019)

47. "Pollen grains in wheat are shed at 3-celled stage while in peas, they are shed at 2-celled stage."Explain where are germ pores present in the pollen grain ? (C.B.S.E. 2017)

48. Explain the process of pollination in Vallisneria. How is it different in water lily which is also anaquatic plant ? (C.B.S.E. 2017, 2019)

49. How many cells are present in the pollen grains at the time of their release from anther ? Name thecells. (C.B.S.E. 2017)

50. (a) Trace the development of an endosperm after fertilisation with reference to coconut. Mention theimportance of endosperm development.

(b) Write the improtance of "pollen bank." (C.B.S.E. 2017)

51. A mature embryo sac in a flowering plant may possess 7-cells but 8 nuclei. Explain with the help ofa diagram only. (C.B.S.E. 2017)

52. In a flowering plant a microspore mother cell produces four male gametophytes while a megasporemother cell form only one female gametophyte. Explain. (C.B.S.E. 2017)

53. Mention the ploidy of the different types of cells present in the female gametophyte of an angiosperm.(C.B.S.E. 2017)

54. Parthenocarpy and apomixis have been observed in some plants. Give an example of each. State asimilarity and a difference observed between the two processes. (C.B.S.E. 2017)

55. Apomixis resembles asexual reproduction as well as mimics sexual reproduction in plants. Explainwith the help of a suitable example. (C.B.S.E. 2017)

��/'�)��%"#('!� #�� )#0�" �&��)��$ 4156. Draw a labelled schematic diagram of T.S. of an anther of an angiosperm. (C.B.S.E. 2017)

57. Draw a sectional view of an apple and label the different parts of an ovary in it. Fruits develop fromovary. Then why is apple referred to as a false fruit. (C.B.S.E. 2017)

58. Differentiate between parthenocarpy and parthenogenesis. Give one example of each. (C.B.S.E. 2018)

59. You are conducting artificial hybridisation on Papaya and Potato. Which one of them would require thesteps of emasculation and why ? However, for both you will use the process of bagging. Justify givingone reason. (C.B.S.E. 2019)

60. It is said that apomixis is a type of asexual reproduction. Justify. (C.B.S.E. 2019)

61. (a) You are given Castor and Bean seeds. Which one of the two would you select to observe theendosperm ?

(b) The development of endosperm precedes that of embnyo in plants. Justify. (C.B.S.E. 2019)

62. Name a distinguishing structure seen in a mature Black Pepper seed and not in Pea seed. State howdoes it develop. (C.B.S.E. 2019)

63. Where exactly is the filiform apparatus present in the embryo sac of an angiosperm ? State itsfunction. (C.B.S.E. 2019)

64. (a) List any two characterstic features of Wheat flowers that make it a good example of wind pollination.

(b) ‘‘It is observed that plant breeders carrying out Wheat hybridisation often take pollen grains fromthe pollen banks.’’ Do you agree ? Give one reason in support of your answer. (C.B.S.E. 2019)

65. When and where do tapetum and synergids develop in flowering plants ? Mention their functions.

(C.B.S.E. 2019)

66. Where are the following structures present in a male gametophyte of an angiosperm ? Mention thefunction of each one of the : (a) Germ pore (b) Sporopollenin (c) Generative cell. (C.B.S.E. 2019)

67. Draw L.S. of an embryo of grass and label its parts. (C.B.S.E. 2019)

68. Draw a diagram of L.S. of Maize grain and label its any six parts. (C.B.S.E. 2019)

1. Describe in sequence the events that lead to the development of a 3-celled pollen grain from microsporemother cell in angiosperms. (C.B.S.E. 2010.)

2. (a) Draw a labelled longisectional view of an albuminous seed ?

(b) How are seeds advantageous to flowering plants ? (C.B.S.E. 2010)

3. Explain double fertilization and trace the post fertilization events in sequential order leading to seedformation in a typical dicotyledonous plant. (C.B.S.E. 2010)

4. Give reasons why

(i) Most zygotes in angiosperms divide only after certain amount of endosperm is formed.

(ii) Groundnut seeds are exalbuminous and Castor seeds are albuminous.

(iii) Micropyle remains as a small pore in the seed coat of a seed.

(iv) Integuments of an ovule harden and the water content is highly reduced as the seed matures.

(v) Apple and Cashew are not called true fruits. (C.B.S.E. 2011)

5. (a) Draw a labelled diagram of L.S. of an embryo of grass (any six labels).

(b) Give reasons for each of the following

(i) Anthers of angiosperm flowers are described as dithecous. (ii) Hybrid seeds have to be produced year after year. (C.B.S.E. 2011)

6. (a) Draw a diagram of an enlarged view of T.S. of one microsporangium of an angiosperm and labelthe following parts : (i) Tapetum (ii) Middle layer (iii) Endothecium (iv) Microspore mother cells.(b) Mention the characteristic features and functions of tapetum.

(c) Explain the following giving reasons : (i) Pollen grains are well preserved as fossils (ii) Pollentablets are in use by people these days. (C.B.S.E. 2011)

42 ��#�%�� #��, #)#&-�.��7. (a) Why is the process of fertilization in angiosperms termed as double fertilization. Explain.

(b) Draw a diagram of an angiospermic embryo sac where fertilization is just completed. Label thefollowing (i) Micropylar and of embryo sac (ii) Part that develops into an embryo (iii) Part thatdevelops into an endosperm (iv) The degenerating cells at chalazal end.

(c) Draw a labelled diagram of globular embryonic stage of an angiosperm. (C.B.S.E. 2011)

8. (a) Explain the characteristic features of wind pollinated flowers. How are insect pollinated flowersdifferent from them ?

(b) Explain the mutually rewarding relationship between Yucca plant and a species of moth.

(C.B.S.E. 2011)

9. How does the megaspore mother cell develop into 7-celled, 8-nucleate embryo sac in an angiosperm ?Draw labelled diagram of a mature embryo sac. (C.B.S.E. 2012)

10. (a) Why is fertilization in an angiosperm referred to as double fertilization ? Mention the ploidy ofthe cells involved.

(b) Draw a neat labelled sketch of L.S. of an endospermous monocot seed. (C.B.S.E. 2012)

11. (a) How does microspore mother cell develop into mature pollen grain in angiosperms ?

(b) Describe the structure of a mature pollen grain and draw a labelled diagram of its two celledstage. (C.B.S.E. 2012)

12. (a) Draw a diagrammatic sectional view of a mature anatropous ovule and label the following partsin it (i) that develops into seed coat (ii) that develops into an embryo after fertilization (iii) thatdevelops into an endosperm in an albuminous seed (iv) through which the pollen tube gains entryinto the embryo sac (v) that attaches the ovule to placenta.

(b) Describe the characteristic features of wind pollinated flowers. (C.B.S.E. 2013)

13. (a) Draw a labelled schematic diagram of the transverse section of a mature anther of an angiospermicplant.

(b) Describe the characteristic features of an insect pollinated flowers. (C.B.S.E. 2013)

14. (a) Draw a diagram of a mature embryo sac of an angiosperm and label the following parts in it (i)Filiform apparatus (ii) Synergids (iii) Central cell (iv) Egg cell (v) Polar nuclei(vi) Antipodals.

(b) Write the fate of egg cell and polar nuclei after fertilization. (C.B.S.E. 2013)

15. (a) Describe the endosperm development in coconut.

(b) Why is tender coconut considered a healthy source of nutrition ?

(c) How are pea seeds different from castor seeds with respect to endosperm ? (C.B.S.E. 2013)

16. (a) Draw a L.S. of a pistil showing pollen tube entering the enbryo sac in an angiosperm and label anysix parts other than stigma, style and ovary. (b) Write the changes a fertilized ovule undergoeswithin the ovary in an angiospermic plant. (C.B.S.E. 2013)

17. (a) Why does endosperm development precede embryo development in angiosperm seeds ? State therole of endosperm in mature albuminous seeds.

(b) Describe with the help of three labelled diagrams the different embryonic stages that includemature embryo of dicot plants. (C.B.S.E. 2014)

18. (a) Explain the phenomenon of double fertilization.

(b) Draw a labelled diagram of a typical anatropous ovule. (C.B.S.E. 2014)

19. (a) Explain the different ways apomictic seeds can develop. Give an example of each.

(b) Mention one advantage of apomictic seeds to farmers.

(c) Draw a labelled mature stage of a dicotyledonous embryo. (C.B.S.E. 2014)

20. A flower of tomato/brinjal plant following the process of sexual reproduction produces 240/360 viableseeds. Answer the following giving reasons :

(a) What is the minimum number of pollen grains that must have been involved in the pollination ofits pistil ?

��/'�)��%"#('!� #�� )#0�" �&��)��$ 43(b) What would be the minimum number of ovules present in the ovary ?

(c) How many megaspore mother cells were involved ?

(d) What is the minimum number of microspore mother cells involved in the above case ?

(e) How many male gametes were involved in this case ? (C.B.S.E. 2015)

(Hint. (a) 240, one for fertilization of one ovule. (b) 240, one ovule for each seed.(c) 240, one MMC for one functional megaspore/embryo sac. (d) 60, each microspore mother cellforms four pollen grains. (e) 480, two from each pollen grain required for double fertilization.)

21. (a) Explain the events after pollination leading to the formation of a seed in angiosperms.

(b) Mention the ploidy levels of the cells of different parts of an albuminous seed. (C.B.S.E. 2015)

(Hint. (b) Seed coat – 2n, embryo – 2n, endosperm – 3n)

22. (a) As a senior biology student you have been asked to demonstrate to the students of secondary levelin your school, the procedure(s) that shall ensure cross pollination in a hermaphrodite flower. Listthe different steps that yon would suggest and provide reason for each one of them.

(b) Draw a diagram of a section of megasporangium of an angiosperm and label funiculus, micropyle,embryo sac and nucellus. (C.B.S.E. 2016)

(Hints. (a) Emasculation to prevent self pollination, bagging, pollination, rebagging).

23. (a) Explain post pollination events leading to seed production in angiosperms. (b) List the differenttypes of pollination depending upon the source of pollen grain. (C.B.S.E. 2016)

24. Explain the events upto fertilization that occur in a flower after the pollen grain has landed on itscompatible stigma. (C.B.S.E. 2017)

25. (a) When a seed of an orange is squeezed, many embryos, instead of one are observed. Explain how itis possible. (b) Are these embryos genetically similar or different ? Comment. (C.B.S.E. 2017)

26. Read the following statement and answer the questions that follow : "A guava fruit has 200 viableseeds." (a) What are viable seeds ? (b) Write the total number of (i) Pollengrains (ii) Gametes inproducing 200 viable guava seeds (c) Prepare a flow chart to depict the post pollination events leadingto viable seed production in a flowering plant. (C.B.S.E. 2017)

27. (a) A Capsicum flower has 240 ovules in its ovary. But it produces a fruit with only 180 viable seeds.Explain giving reason that could be responsible for such a result. (b) Describe the development of anendosperm in a viable seed. Why does endosperm development precede embryo development ?(c) Give an example of an angiosperm seed that has a perisperm. Name the part the perispermdevelops from. (C.B.S.E. 2017)

28. (a) Name the types of flowers produced by Viola (Pansy). How do they differ from each other ?(b) Describe the kind of pollnation in one of the types of flowers that ensures seed-set production.(c) Describe the process of pollination in Vallisneria. (C.B.S.E. 2017)

29. (a) Geitonogamy and xenogamy, both require pollinating agents. Yet they are very different from eachother. Explain how.(b) Describe the characteristics of flowers that are pollinated by wind. (C.B.S.E. 2017)

30. (a) Describe any two devices in a flowering plant which prevent both autogamy and geitonogamy.(b) Explain the events upto double fertilization after the pollen tube enters one of the synergids in anovule of an angiosperm. (C.B.S.E. 2018)

31. (a) Explain the process of double fertilisation in angiosperms.(b) Why does the development of endosperm precede that of embryo ?(c) List parts of a typical dicot embryo. (C.B.S.E. 2019)

32. (a) Explain the role of stigma in pollen-pistil interactions.

(b) Decribe the post-pollination events leading to double fertilisation in angiosperms, starting with atwo celled pollen grain. (C.B.S.E. 2019)

33. (a) Explain any two ways by which apomictic seed can develop.

(b) List one advantage and one disadvantage of an apomictic crop.

(c) Why do farmers find production of hybrid seeds costly ? (C.B.S.E. 2019)

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1. Name the parts of angiosperm flower in which development of male and female gametophytestake place.

Ans. Anther, Ovary.

2. Differentiate between microsporogenesis and megasporogenesis. Which type of cell divisionoccurs during these events ? Name the structures formed at end of these two events.

Ans. Differences Between Microsporogenesis and Megasporogenesis. See text.

Type of Division. Meiosis

End Products. Microsporogenesis—microspores or pollen grains.

Megasporogenesis—megaspores, one megaspore forming embryo sac.

3. Arrange the following terms in correct developmental sequence : Pollen grain, sporogenoustissue, microspore tetrad, pollen mother cell, male gametes.

Ans. Sporogenous tissue–Pollen mother cell–Microspore tetrad–Pollen grain, Male gametes.

4. With a neat labelled diagram, describe the parts of a typical angiosperm ovule.

Ans. Ovule. It is an oval whitish structure which is borne over a parenchymatous cushion or placenta

inside the ovary part of the flower. The different parts are as follows :

Draw fig. 2.13.

1. Funicle. It is stalk of the ovule with which it is attached to placenta. The point over the

body of the ovule where funicle comes in contact with it is called hilum. In anatropous or

inverted ovules, funicle is also fused with the body of the ovule and form a ridge named raphe.

2. Integuments. They are one or two multicellular cuticularised coverings of theovule. A small pore called micropyle is left out at one end. The end opposite tomicropyle where the integuments originate is termed as chalaza.

3. Nucellus. It represents the body of ovule or megasporangium. Nucellus consists of parenchymacells that store a lot of reserve food.

4. Embryo Sac. It is a nearly oval gametophytic structure embedded in the nucellus. Embryo sacis surrounded by an extremely thin pecto-cellulosic covering. Internally, it contains sevencells — one large binucleate or diploid central cell, three micropylar cells and three chalazalcells. Micropylar cells form an egg apparatus with one large egg or oosphere and twosynergids or help cells. The chalazal cells are also called antipodal cells. All cells of embryosac are connected by plasmodesmata.

5. What is meant by monosporic development of female gametophyte ?

Ans. Female gametophytes or embryo sacs develop from haploid megaspores. One, two or all the fourmegaspores may take part in the formation of a female gametophyte. In monosporic development,the female gametophyte or embryo sac grows from a single functional megaspore. The remainingthree megaspores degenerate.

6. With a neat diagram explain 7 celled, 8 nucleate nature of female gametophyte.

Ans. Female gametophyte or embryo sac is a small oval structure embedded in the micropylar half ofthe nucellus. It is covered by a thin membranous wall of pectocellulose (Chebotaru, 1975). Thefemale gametophyte contains three celled egg apparatus, three antipodal cells and one binucleatecentral cells (seven cells and eight nuclei).

Oosphere or egg is slightly larger than synergids with vacuole in micropylar region. Acovering wall is present which is thin towards the chalazal end. Lateral hooks are absent.Filiform apparatus may be present or absent.

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1. Egg Apparatus. It is a triangular grouping of three pyriform cells present in the micropylarend of embryo sac. There are two synergids and one egg. Synergids or help cells havelateral hooks, filiform apparatus and a wall that thins out towards chalazal end. A vacuoleis present towards this end. Synergids take part in (a) Absorption of nourishment.(b) Chemotactic attraction of pollen tube. (c) Shock absorption of ingrowing pollen tube.(d) Function as seat for pollen tube discharge.

2. Antipodal Cells. They are a group of three vegetative cells of various shapes and sizeswhich occur towards chalazal end of embryo sac. The cells may take part in absorption ofnourishment from nucellus.

3. Central Cell. It is the largest cell that is bounded by a membrane of embryo sac. There aretwo nuclei called polar nuclei. Cytoplasm is vacuolated. Reserve food is present. The twopolar nuclei often fuse in the centre to produce a single diploid fusion nucleus. Afterfertilization the central cell gets converted into triploid primary endosperm cell.

7. What are chasmogamous flowers ? Can cross-pollination occur in cleistogamous flowers ?Give reasons for your answer.

Ans. Chasmogamous Flowers. These are open flowers with exposed stigma and stamens.

No cross-pollination occurs in cleistogamous flowers, as flowers are closed and no transfer ofpollen is possible.

8. Mention two strategies evolved by flowers to prevent self pollination.

Ans. (i) Dichogamy or maturation of anthers and stigmas at different times in a bisexual flower.

(ii) Production of unisexual flowers.

9. What is self-incompatibility ? Why does self pollination not lead to seed formation in selfincompatible species ?

Ans. Definition. Self incompatibility or self sterility is the inability of an intersexual or bisexualplant to produce viable seeds on self pollination despite producing functional male and femalegametes.

Reason. Self incompatibility is genetically controlled by a multiallelic S–gene. Occurrence of

similar allele in pollen grain and stigma or style (e.g., S1 and S1S2) results in failure of pollen grain

to complete its growth and effect fertilization. As a result no seed is formed.

10. What is bagging technique ? How is it useful in a plant breeding programme ?

Ans. Definition. Bagging technique is the covering of flowers with polythene or paper bags toprevent their contamination from foreign pollen as during breeding programmes. Bags areremoved only during hand pollination to collect desired pollen and to dust them over thereceptive stigmas of female plant.

Uses in Plant Breeding. (i) Prevention of contamination with foreign pollen.

(ii) Prevention of damage by animals.

(iii) Prevention of germination of foreign pollen over the stigma.

56 ��#�%�� #��, #)#&-�.��11. What is triple fusion ? Where and how does it take place ? Name the nuclei involved in

triple fusion.

Ans. Triple Fusion. It is the name of vegetative fertilization which involves the fusion of a malegamete with the secondary or fusion nucleus of central cell to produce triploid primaryendosperm cell.

Nuclei Involved. Three nuclei are involved in triple fusion— one nucleus of male gamete andtwo polar nuclei or their fusion product called secondary nucleus.

12. Why do you think the zygote is dormant for some time in a fertilized ovule ?

Ans. Zygote is dormant for some time in a fertilized ovule so that certain amount of endosperm isformed first. Such dormant phase assures nutrition to the developing embryo because zygotedivides only after certain amount of endosperm is formed.

13. Differentiate between : (a) hypocotyl and epicotyl; (b) coleoptile and coleorhiza;(c) integument and testa; (d) perisperm and pericarp.

Ans. (a) Differences Between Epicotyl and Hypocotyl. See text.

(b) Differences Between Coleoptile and Coleorhiza. See text.

(c) Diferences Between Integument and Testa. See text.

(d) Differences Between Perisperm and Pericarp. See text.

14. Why is the apple called a false fruit ? Which part of the flower forms the fruit ?

Ans. Apple is called false fruit because during its formation thalamus grows around the pericarp toproduce the fleshy edible part.

Fruit is formed from ovary part of the flower. In false fruit, some additional part of flower getsfused with it.

15. What is meant by emasculation ? When and why does a plant breeder employ this technique ?

Ans. Definition. Emasculation is the practice of removal of anthers in their bud condition frombisexual flowers selected as female parents in breeding programmes.

When Required. While using a bisexual or intersexual flower as female parent. It has to becarried out in the bud condition before the anthers begin to differentiate.

Why Required. To prevent chances of self pollination.

16. If one can induce parthenocarpy through the application of growth substances, which fruitsyou would select to induce parthenocarpy and why ?

Ans. Only fleshy fruits are selected for inducing parthenocarpy. Here seeds are irritant and oftenremoved before consumption, e.g., Orange, Water Melon. Parthenocarpic fruits are also importantfor fruit processing industry and fruits grown in green houses where natural pollinators are notavailable.

17. Explain the role of tapetum in the formation of pollen grain wall .

Ans. Tapetum in Wall Formation. (i) Secretion of Ubisch granules which provide sporopolleninand other materials for exine formation of pollen grains. (ii) Secreting pollen kitt for forming acovering around entomophilous pollen grains. (iii) Secreting callase to dissolve common callosecovering around the microspores.

18. What is apomixis and what is its importance ?

Ans. Apomixis. It is the formation of new individuals or seeds with embryo growing directly fromdiploid cells of nuclleus or integument (e.g., Mango, Orange), diploid egg or some othergametophytic cell (e.g., Apple, Rubus).

Importance. Apomixis has the potential to maintain hybrid vigour indefinitely even in those cropplants (e.g., cereals, legumes) where vegetative reproduction is not possible. Apomixis is geneticallycontrolled. Incorporation of genes for apomixis and prevention of pollination are required for this.

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1. Even though each pollen grain has two male gametes, why are atleast 10 pollen grains andnot 5 pollen grains required to fertilize 10 ovules present in a particular carpel ?

Ans. 1. It is the pollen tube and not the individual male gamete which enters an ovule.

2. Both the male gametes are used up in fertilizing two different structures in angiosperms–germinative fertilization or syngamy and vegetative fertilization or triple fusion.

Therefore, 10 pollen tubes or pollen grains are required to fertilize 10 ovules.

2. Why does a beekeeper keep beehives in crop fields during flowering periods ? State anytwo advantages.

Ans. Advantages. 1. Easy availability of honey to bees.

2. Ensuring pollination of crop plants.3. With the help of labelled diagram, depict the stages of a microspore maturing into a pollen

grain.Ans. Draw Figure 2.7.

4. (a) Draw a longitudinal sectional view of a typical anatropous ovule to show the site wheredouble fertilization takes place. Label any four major parts of the ovule.

(b) How do the male gametes that are present in the pollen grains reach the site mentionedby you in part (a) to cause double fertilization ?

Ans. (a) Draw Figure 2.13.

Site of Double Fertilization. (i) Oosphere (ii) Central cell.(b) By means of pollen tube. Pollen tube is formed by tube cell of the pollen grain. It travels

through the style along transmission or conducting tissue and inside the ovary towards

ovule along obturator. Movement is chemotropic along increasing concentration of calcium- boron - inositol. In the ovule it is attracted by a synergid to which it penetrates and burstsopen to release both the male gametes, one for fusion with oosphere and the other for fusion

with central cell.5. If the chromosome number of plant species is 16, what would be the chromosome number

and the ploidy level of the (i) microspore mother cell and (ii) the endosperm cells ?

Ans. Plant — diploid — 16 chromosomesMicrospore Mother Cell — diploid — 16 chromosomes

Endosperm Cells — triploid — 16

2�� = 24 chromosomes.

6. (a) Draw the embryo sac of a flowering plant and label (i) central cell (ii) chalazal end ofthe embryo sac (iii) synergids (b) Name the cell that develops into embryo sac and

explain how this cell leads to the formation of embryo sac. Also mention the roleplayed by the various cells of the embryo sac.

Ans. (a) Draw figure 2.15.

(b) (i) Functional megaspore develops into embryo sac.(ii) Functional megaspore grows in size. Its nucleus divides mitotically into two. The two

nuclei move to opposite poles. They divide twice forming four nuclei at each pole. One

nucleus of each group called polar nucleus, passes towards the centre. Cytoplasm undergoescleavage around the nuclei at the two ends to form cells, three at each end. A total of sevencelled and eight nucleate gemetophyte is formed. It is called embryo sac. Micropylar

triplet is called egg apparatus. It consists of an oosphere and two synergids. Chalazaltriplet consists of antipodal cells. The seventh binucleate cell is called central cell.

5� ��#�%�� #��, #)#&-�.��(iii) Functions. 1. Oosphere or Egg. Female gamete. Fuses with one male gamete to produce

zygote or future embryo.2. Synergids. Absorption of nourishment, attract pollen tube and one acts as shock absorber.3. Central Cell. After fusion with second male gamete it produces primary endosperm cellwhich gives rise to nutrient tissue called endosperm.4. Antipodal Cells. Vegetative cells with function of absorbingnourishment in several cases.

7. In the adjacent figure of a typical dicot embryo, label theparts (1), (2) and (3). State the function of each of the labelledpart.

Ans. (1) Plumule(2) Cotyledons(3) RadiclePlumule. To form shoot systemRadicle. To form root system.Cotyledons (Seed Leaves). In this case storage of food.

SAMPLE PAPERSAMPLE PAPERSAMPLE PAPERSAMPLE PAPERSAMPLE PAPER�201020102010201020101. The meiocyte of an Onion plant contains 32 chromosomes. Work out the number of chromosomes

found in its endosperm.Ans. Meiocyte is diploid (2n) while endosperm is triploid (3n). Haploid chromosome number (n) in

Onion as 32/2 = 16 chromosomes. Endosperm being triploid has 16 × 3 = 48 chromosomes.2. Identify the type of flowers shown in A and B. Which of the two will produce an assured

seed set.

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Ans. A—Chasmogamous flower. B—Cleistogamous flowers. Cleistogamous flowers produce assuredseed set as they do not depend upon external agency for pollination.

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3. Draw a labelled diagram of the sectional view of a mature pollen grain of angiosperms.Explain the functions of any two of its parts.

Ans. Functions. (i) Exine. Made of most resistantbiological substance sporopollenin, it providesprotection to pollen grain.

(ii) Intine. Made of cellulose and pectin, it latergrows to form pollen tube.(iii) Generative Cell. It gives rise to two malegametes.(iv) Vegetative or Tube Cell. It stores food andlater grows to form cytoplasmic contents of thepollen tube.

4. ‘‘Incompatibility is a natural barrier in the fusion of gametes.’’ Justify the statement.Ans. Incompatibility is genetically determined inability of gametes to fuse. This is an important

tool that prevents unwanted fertilizations.In plants incompatibility-compatibility reaction occurs over the surface of stigma. The reactionis between proteins present over the surface of the stigma and the pollen grains. It is a sort ofrecognition reaction.The unwanted or incompatible pollen normally do not germinate over the stigma. Only thecompatible pollen grains absorb water and nutrients. They develop pollen tubes for performingfertilization.The chemical interactions for determining compatibility-incompatibility continues in the styleand the ovary. The poorly compatible pollen grains are slow to germinate. Their pollen tubesmay abort midway.Understanding the incompatible reactions is important. The chemicals involved in incompatibilitycan be neutralised so that any desirable cross can be performed.

SAMPLE PAPERSAMPLE PAPERSAMPLE PAPERSAMPLE PAPERSAMPLE PAPER�2012-132012-132012-132012-132012-131. The following describe the wind pollinated plants. Which one of these statements is

incorrect ?(i) The pollen grains are sticky (ii) Stamens are well exposed.(iii) Flowers often have a single ovule.

Ans. (i) The pollen grains are sticky.2. (a) Draw a well labelled diagram of the sectional view of a typical anatropous ovule.

(b) Mention of fate of all the components of the embryo sac after fertilization.Ans. (a) Draw Fig. 2.13

(b) Fate of Embryo Sac Components1. Oosphere (Egg Cell). Forms zygote (2n) and then embryo.2. Synergids. Degenerate3. Antipodal Cells. Degenerate4. Central Cell (Polar Nuclei + Male Gamete). Endosperm (3n). May persist or get consumed.

SAMPLE PAPERSAMPLE PAPERSAMPLE PAPERSAMPLE PAPERSAMPLE PAPER—2013-142013-142013-142013-142013-141. If the stamens are well exposed, usually which mode of pollination the plant is expected to

follow.Ans. Anemophily or wind pollination.

2. (a) Draw a labelled diagram of the sectional view of a typical anatropous ovule.(b) Mention the fate of all the components of the embryo sac after fertilization.

Ans. See Q. 2. of Sample Paper 2012–13

SAMPLE PAPERSAMPLE PAPERSAMPLE PAPERSAMPLE PAPERSAMPLE PAPER—2014-152014-152014-152014-152014-151. Draw and label the enlarged view of microsporangium. State the function of its innermost

layer.Ans. Draw and label Fig. 2.4. E.

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SAMPLE PAPERSAMPLE PAPERSAMPLE PAPERSAMPLE PAPERSAMPLE PAPER—2015-162015-162015-162015-162015-161. During an excavation assignment, scientists collected pollen grains of a plant preserved in

deaper layers of soil. Analyse the properties of pollen grains which help in fossilisation.Ans. Pollen grains are very difficult to degrade and deceompose. They, therefore, undergo fossilisation

easily. It is due to presence of exine over their surface. Pollen grain exine is made ofsporopollenin. Sporopollenin is the most resistant biological product. No enzyme is known todegrade it. Heat, acids and alkalies have little effect on it.

SAMPLE PAPERSAMPLE PAPERSAMPLE PAPERSAMPLE PAPERSAMPLE PAPER—2016-17, 2017-182016-17, 2017-182016-17, 2017-182016-17, 2017-182016-17, 2017-181. Draw and label the enlarged view of microsporngium of an Angiosperm. State the function

of its innermost wall layer.

Ans.

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T.S. young microsporngium

Function of Innermost Layer or Tapetum. It nurishes the developing pollen grains and providesthem with sporopollenin, pollenkitt, growth hormones and compatibility-incompatibility proteins.

SAMPLE PAPERSAMPLE PAPERSAMPLE PAPERSAMPLE PAPERSAMPLE PAPER—2018-192018-192018-192018-192018-191. How many pollen grains and ova are likely to be formed in the anther and the ovary of an

angiospem bearing 25 microspore mother cells and 25 megasphore mother cells respectively ?Ans. Pollen grains— 25 × 4 = 100

Ova — 25 × 1 = 25. They will occur in 25 ovules.2. In case of polyembryony, an embryo A develops from the synergid and embryo B develops

from the nucellus. State the ploidy of embryo A and B.Ans. Ploidy of A = Haploid

Ploidy of B = Diploid.3. Comment upon the mode of pollination in Vallisneria and Eichhornia which have emergent

flowers.Ans. (i) Flowers of aquatic plant Eichhornia are emergent. They are pollinated by wind and bees.

(ii) In submerged aquatic plant Valliseria, male flowers rise to the surface of water and floatthere. The female flowers also rise to the surface and get pollinated by male flowers coming incontact with them.

4. The embryo sac in female gametophyte is seven celled and eight nucleated structure.Justify the statement with the help of labelled diagram.

Ans. See N.C.E.R.T. Question 6.5. List the changes that occur when an ovule matures into seed.

Ans. (i) Outer integument grows and hardens into a thick and tough protective seed coat or testa. (ii) Inner integument matures into a papery inner seed coat.(iii) Micropyle remains as pore of the seed coat.(iv) Metabolic activity decreases and comes to a near stop.(v) Water content drops to 10–15%.(vi) The embryo becomes inactive or dormant.

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SAMPLE PAPERSAMPLE PAPERSAMPLE PAPERSAMPLE PAPERSAMPLE PAPER—2019-202019-202019-202019-202019-201. Draw a well-labelled diagram of L.S of a pistil of a flower

showing the passage of growing pollen tube upto its destination.Ans. L.S. pistil. ��

2. “Apomixis is a form of asexual reproduction that mimics sexualreproduction in plants.” Explain with the help of a suitableexample.

Ans. Apomixis is the formation of embryo and seed asexually withoutproducing and fusion of gametes. This can occur by two methods.(i) Diploid Egg. The embryo has a diploid egg due to absence ofmeiosis in megaspore mother cell. The diploid egg directly formsthe embryo without fertilization, e.g. Pea, Apple.(ii) Sporophytic Budding. Diploid cell of integument or nucellusdevelops directly into embryo which pushes the normal embryo andreplaces it. As the diplloid embryo is developing, changes occur in the ovule to form a seede.g. Mango, Orange, Opuntia, Onion.Apomixis has a big biological importance in that once a hybrid has been formed, it can bepropagated indefinitely without loss of vigour and vitality. It is, however, accompanied bypolyembryony. Separation of apomictic embryo is quite difficult.

�� 1. The given figure is part of T.S. of a microsporangium.

(a) What is the function of microspore mother cells ? How is itperformed ?

(b) What is the role of(i) Tapetum and

(ii) Endothecium in the microsporangium ?Ans. (a) Microspore mother cells produce pollen grains, also called

microspores. Microspore mother cells are diploid while pollengrains are haploid. For pollen formation, microspore mother cellsundergo meiosis.

(b) (i) Tapetum. It provides nourishment to microspore mother cells and young microspores, a part ofsporopollenin and compatibility proteins to pollen grains.

(ii) Endothecium. In many anthers, endothecium cells enlarge, develop fibrous thickenings andhelp in rupturing of the anther.

1. Fill in the blanks

(i) The term apomixis was given by ......... .

(ii) Apomixis is unusual sexual reproduction where there is no ......... and ......... .

(iii) Apomixis is mainly of two types, ......... and ......... .

(iv) Development of embryos directly from sporophytic tissue like ......... and ......... isadventive embryony.

(v) Development of embryo sac directly from cell of nucellus (2n) is called ......... .

(vi) Development of fruits without fertilization is ......... . (C.B.S.E. Main 2005)

Ans. (i) Winkler (1908) (ii) (a) meiosis (b) syngamy (iii) (a) recurrent (b) noncurrent (iv) (a) nucellus(b) integument (v) apospory (vi) parthenocarpy

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2. Define double fertilization. (C.B.S.E. Main 2006)

Ans. Double Fertilization. It is fusion of two male gametes brought by a single pollen tube with twodifferent cells of the same female gemetophyte to form two different structures (zygote andprimary endosperm cell).

3. Define (i) Apomixis (ii) Allogamy. (C.B.S.E. Main 2006)

Ans. (i) Apomixis. See NCERT Q. 18. (ii)

Allogamy. It is the transfer of pollen grains from anther of one flower to the stigma of

another flower. Allogamy is of two types, xenogamy and geitonogamy.

4. Answer the question based on the

following figure.

Which type of ovule is shown in the

figure. Give one reason.

(C.B.S.E. Main 2007)

Ans. Anatropous (inverted).

Reason. Funicle is fused with the body

of the ovule with basal chalaza at one

end and apical micropyle at the other

end near the hilum.

5. Pollination between different flowers of the same plant is called ........... .

(C.B.S.E. Main 2007)

Ans. Geitonogamy.

6. Write location and function of synergid. (C.B.S.E. Main 2007)

Ans. Location. Micropylar end of embryo sac.

Function. See NCERT Question 6.

7. Given below is an enlarged view of one microsporangium of a mature anther.

(i) Name 'a', 'b' and 'c' wall layers.

(ii) Mention the characteristics and functions of the

cells forming wall layer 'c'. (C.B.S.E. 2008 Comptt.)

Ans. 'a' – endothecium, 'b' – middle layers,

'c' – tapetum.

Tapetum. Characteristics. The cells

become large multinucleate and polyploid.

Functions. (i) Nourishing the sporogenous

cells and their derivatives.

(ii) Secreting hormones, Ubisch granules

(for sporopollenin and other exine

components), pollenkitt and compatibility-

incompatibility proteins for pollen grains.

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'b' and mention their function. (C.B.S.E. 2009, 2019)

Ans. "a" Sporogenous tissue.

Function. Formation of microspore mother cells and after

their meiosis production of microspores (pollen grains).

"b" Tapetum.

Function. See text.

9. (a) Identify the figure.

(b) Name the initial cell from which

this structure has developed.

(c) Draw the next mature stage and label the parts. (C.B.S.E. 2009)

Ans. (a) Globular stage of dicot embryo. (b) Zygote.

(c) Heart shaped stage of dicot embryo. Draw Fig. 2.29 H.

10. Fill in the blanks :

Both Maize and ............. are monoecious plants. They can preventautogamy but not .............. . (C.B.S.E. 2009)

Ans. Castor, geitonogamy.

11. (a) Name the structure the parts 'A' and 'B' shown in the diagram

respectively develop into.

(b) Explain the process of development which 'B' undergoes inalbuminous and exalbuminous seeds. Give one example of each

of these seeds.

Ans. (a) Products. 'A' gives rise to embryo. 'B' forms endosperm.

(b) Development. 'B' is triploid cell. It grows to formnutrient storing endosperm. Embryo is always in contact

with endosperm and obtains its nourishment from the same.

In exalbuminous (non– endospermic) seeds, the endospermin completely consumed by developing embryo. Nutrition

for future growth of embryo generally gets stored incotyledons, e.g., pea, gram, groundnut.

In albuminous (endospermic) seeds, the nutrient richendosperm persists in the mature seed, e.g., castor, maize.

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1. Female gametophyte of angiosperms isrepresented by

(A) Ovule

(B) Megaspore mother cell

(C) Embryo sac

(D) Nucellus. (C.E.T. Chd. 2001)

2. Formation of embryo directly from nucellusand integument is

�� (A) Adventitive polyembryony

(B) Apospory

(C) Apogamy (D) Apomixis.(B.H.U. 2001, C.B.S.E. 2001)

3. Function of tapetum is(A) Protective (B) Nutritive(C) Respiratory (D) All the above.

(B.H.U. 2001)

54 ��#�%�� #��, #)#&-�.��4. Sexual reproduction of flowering plants was

discovered by

(A) Camerarius (B) Nawaschin

(C) Strasburger (D) Maheshwari.

(A.F.M.C. 2001)

5. Egg apparatus consists of

(A) Egg and antipodals

(B) Polar nuclei

(C) Egg and synergids

(D) Egg. (A.F.M.C. 2001)

6. During formation of pollen grains, amicrospore mother cell undergoes

(A) One meiotic division

(B) One mitotic division

(C) One meiotic and one mitotic division

(D) One meiotic and two mitotic divisions.

(C.B.S.E. 2001)

7. Anemophily occurs in

(A) Salvia (B) Vallisneria

(C) Coconut (D) Bottle Brush.

(C.B.S.E. 2001)

8. Cross pollination is preferred over selfpollination because it

(A) Produces better offspring

(B) Forms new varieties

(C) Induces parthenogenesis

(D) Is economical. (A.F.M.C. 2001)

9. Night blooming flowers are generally

(A) Light weight

(B) White

(C) Brightly coloured

(D) Bloom in clusters. (Manipal 2001)

10. Anemophily is pollination through

(A) Water (B) Air

(C) Insects (D) Worms.

(K.C.E.T. 2001)

11. Fertilization occurs in Casuarina through

(A) Porogamy (B) Mesogamy

(C) Chalazogamy (D) Apogamy.

(B.H.U. 2002)

12. Contrivance for self pollination is

(A) Homogamy (B) Bisexuality

(C) Cleistogamy (D) All the above.

(J.K.C.E.T. 2002)

13. Xenia and metaxenia are connected with

(A) Xylem and Phloem

(B) Pollen and endosperm

(C) Pollen culture

(D) Endosperm only. (A.I.I.M.S. 2002)

14. In flowering plants, archesporium forms

(A) Wall of sporangium

(B) Wall and tapetum

(C) Wall and sporogenous cells

(D) Tapetum and sporogenous cells.

(C.B.S.E. 2003)

15. Part of plant having two generations, onewithin other is

(A) Unfertilised ovule

(B) Seed

(C) Germinated pollen grain

(D) Embryo. (A.I.I.M.S. 2003)

16. A tetraploid male plant is crossed withdiploid female plant. Ploidy of endospermwill be

(A) Diploidy (B) Triploidy

(C) Tetraploidy (D) Pentaploidy.

(C.B.S.E. 2004)

17. Device for self pollination is

(A) Dicliny (B) Unisexuality

(C) Heterostyly (D) None of the above.

(J.K.C.M.E.E. 2004)

18. Pollen tube enters the embryo sac

(A) Directly passes into egg

(B) Through one of the synergids

(C) Between synergid and central cell

(D) Through one of the antipodal cells.

(A.I.I.M.S. 2004)

19. Double fertilization results in production of

(A) Haploid nucleus (B) Diploid nucleus

(C) Triploid nucleus(D) Tetraploid nucleus.

(J.K.C.E.T. 2005)

20. Development of seed from an unfertilizedegg is

(A) Vivipary (B) Parthenocarpy

(C) Apogamy (D) Apospory.

(H.P.P.M.T. 2005)

21. In typical embryo sac, the nuclei arearranged as

(A) 3+2+3 (B) 3+3+2

(C) 2+3+3 (D) 2+4+2.

(C.B.S.E 2006)

��/'�)��%"#('!� #�� )#0�" �&��)��$ 5522. What would be chromosome number of cells

in aleurone layer if megaspore mother cellhas ten chromosomes ?(A) 10 (B) 15(C) 20 (D) 25. (Odisha 2006)

23. What would be the number of chromosomesin the cells of the aleurone layer in a plantspecies with 8 chromosomes in itssynergids ?(A) 16 (B) 24(C) 32 (D) 8. (C.B.S.E. 2007)

24. Study of pollen grains is(A) Palynology (B) Ethmology(C) Palaeobotany (D) �-taxonomy.

(W.B. 2008)25. Which one is triploid ?

(A) Megaspore (B) Embryo(C) Endosperm (D) Microspore.

(Odisha 2008)26. Unisexuality of flowers prevents

(A) Geitonogamy but not xenogamy(B) Autogamy but not geitonogamy(C) Autogamy and geitonogamy(D) Both geitonogamy and xenogamy.

(C.B.S.E. 2008, N.E.E.T. 2017)27. Secondary nucleus is formed by

(A) Antipodal cells (B) Egg apparatus(C) Synergids (D) Two polar nuclei.

(M.H.C.E.T. 2008)28. Which plant part having two generations,

one within the other is(A) Embryo(B) Germinated pollen grain(C) Unfertilized ovule(D) Seed. (A.I.I.M.S 2008)

29. Assured seed set is possible even in absenceof pollination in flowers which are(A) Chasmogamous (B) Cleistogamous(C) Xenogamous (D) Geitonogamous.

(A.M.U. 2009)30. Which type of pollination brings genetically

different types of pollen grains to the stigma(A) Cleistogamy (B) Xenogamy(C) Autogamy (D) Geitonogamy

(H.P.P.M.T. 2010)31. Apomictic embryos in Citrus arise from

(A) Maternal sporophytic tissue in ovule(B) Antipodal cells (C) Diploid egg(D) Synergids. (C.B.S.E. 2010)

32. What would be the number of chromosomesof aleurone cells of a plant with 42chromosomes in its root tip cells.(A) 84 (B) 21(C) 42 (D) 63.(C.B.S.E. 2011)

33. In which of the following pollination isautogamous(A) Chasmogamy (B) Cleistogamy(C) Geitonogamy (D) Xenogamy.

(C.B.S.E. 2011)34. What is common between vegetative

reproduction and apomixis(A) Both occur round the year(B) Both produce progeny identical to the

parent(C) Both are applicable to only dicot plants(D) Both bypass the flowering phase.

(C.B.S.E. Main 2011)35. Both autogamy and geitonogamy are

prevented in(A) Castor (B) Maize(C) Papaya (D) Cucumber.

(C.B.S.E. 2012)36. Xenogamy is a type of

(A) Allogamy (B) Autogamy(C) Homogamy (D) Cleistogamy.

(W.B. 2012)37. Plants with ovaries having one or a few

ovules are commonly pollinated by(A) Birds (B) Wind(C) Bees (D) Butterflies.

(C.B.S.E. Main 2012, N.E.E.T. 2017)38. Body of ovule is attached to funicle at a

point called

(A) Hilum (B) Micropyle

(C) Integuments (D) Chalaza.(A.M.U. 2013)

39. Megasporangium is equivalent to

(A) Embryo sac (B) Ovule

(C) Fruit (D) Nucellus.(N.E.E.T. 2013)

40. Scutellum is part of

(A) Dicot embryo (B)Monocot embryo

(C) Pistil (D) Leaf bud.(Uttarakhand 2014)

41. Which one of the following statements iscorrect

(A) Mango is a parthenocarpic fruit

(B) A proteinaceous aleurone layer ispresent in Maize grain.

(C) A sterile pistil is called staminode

(D) The seed in grasses is not endospermic.

(C.B.S.E. 2014)

�66 ��#�%�� #��, #)#&-�.��42. Malacophily is pollination by

(A) Insects (B) Birds

(C) Snails (D) Mammals.

(W.B. 2015)

43. Filiform apparatus is characteristic featureof

(A) Generative cell (B) Nucellar embryo

(C) Aleurone cell (D) Synergids.

(C.B.S.E. 2015)

44. Water pollinated plants have

(A) Bright colour (B) Fragrance

(C) Nectar (D) Tassels

(E) Mucilage covering over pollen grains.

(Kerala 2016)

45. Coconut water from tender Coconutrepresents

(A) Free nuclear endosperm

(B) Endocarp

(C) Fleshy mesocarp

(D) Free nuclear proembryo.

(N.E.E.T.-I 2016)

46. Functional megaspore of an angiospermdevelops into

(A) Embryo (B) Embryo sac

(C) Ovule (D) Endosperm.(N.E.E.T. 2017)

47. Attractants and rewards are required for

(A) Anemophily (B) Entomophily

(C) Hydrophily (D) Cleistogamy.(N.E.E.T. 2017)

48. Ploidy of nucellus, endosperm, polar nuclei,megaspore mother cell and femalegametophyte is respectively

(A) 2n, 3n, n, 2n, n

(B) 2n, 3n, 2n, 2n, n

(C) 2n, 3n, 2n, n, n

(D) n, 2n, n , 2n, n. (A.I.I.M.S. 2018)

49. Double fertilization is

(A) Fusion of two male gametes with oneegg

(B) Fusion of one male gamete with twopolar nuclei

(C) Fusion of two male gametes of a pollentube with two different eggs.

(D) Syngamy and triple fusion.

(N.E.E.T. 2018)

50. Persistent nucellus in the seed is knownas

(A) Chalaza (B) Perisperm

(C) Hilum (D) Tegmen.(N.E.E.T. 2019)

51. What is the fate of male gametesdischarged in the synergid

(A) One fuses with egg, other degenerates

(B) All fuse with egg

(C) One fuses with egg, other fuses withsynergid

(D) One fuses with egg, other fuses withcentral cell nuclei. (N.E.E.T. 2019)

1. (C) 2. (D) 3. (B) 4. (A) 5. (A) 6. (A) 7. (C) 8. (A) 9. (B) 10. (B)

11. (C) 12. (D) 13. (B) 14. (C) 15. (A) 16. (C) 17. (D) 18. (B) 19. (C) 20. (C)

21. (A) 22. (B) 23. (B) 24. (A) 25. (C) 26. (B) 27. (D) 28. (D) 29. (B) 30. (B)

31. (A) 32. (D) 33. (B) 34. (B) 35. (C) 36. (A) 37. (B) 38. (A) 39. (D) 40. (B)

41. (B) 42. (C) 43. (D) 44. (E) 45. (A) 46. (B) 47. (B) 48. (A) 49. (D) 50. (B)

51. (D)

1. Among the terms listed below those thatare not technically correct names for afloral whorl are : (i) Androecium (ii) Carpel

(iii) Corolla (iv) Sepal.

(A) i and iv (B) iii and iv

(C) ii and iv (D) i and ii.

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an anther.

(A) Stamen (B) Filament

(C) Pollen grain (D) Androecium.

3. In a typical complete, bisexual andhypogynous flower the arrangement of floralwhorl on the thalamus from the outermostto the innermost is :

(A) Calyx, corolla, androecium andgynoecium

(B) Calyx, corolla, gynoecium andandroecium

(C) Gynoecium, androecium, corolla andcalyx

(D) Androecium, gynoecium, corolla andcalyx.

4. A dicotyledonous plant bears flowers butnever produces fruits and seeds. The mostprobable cause for the above situation is(A) Plant is dioecious and bears only

pistillate flowers(B) Plant is dioecious and bears both

pistillate and staminate flowers.(C) Plant is monoecious(D) Plant is dioecious and bears only

staminate flowers.

5. The outermost and innermost wall layersof microsporangium in an anther arerespectively(A) Endothecium and tapetum(B) Epidermis and endodermis(C) Epidermis and middle layer(D) Epidermis and tapetum.

6. During microsporogenesis, meiosis occursin(A) Endothecium(B) Microspore mother cells(C) Microspore tetrads(D) Pollen grains.

7. From among the sets of terms given below,identify those that are associated with thegynoecium(A) Stigma, ovule, embryo sac, placenta

(B) Thalamus, pistil, style, ovule

(C) Ovule, ovary, embryo sac, tapetum

(D) Ovule, stamen, ovary, embryo sac.

8. Starting from the innermost part, the correctsequence of parts in an ovule are

(A) Egg, nucellus, embryo sac, integument

(B) Egg, embryo sac, nucellus, integument

(C) Embryo sac, nucellus, integument, egg

(D) Egg, integument, embryo sac, nucellus.

9. From the statements given below choosethe options that are true for a typical femalegametophyte of a flowering plant

(i) It is 8-nucleate and 7-celled at maturity

(ii) It is free nuclear during the development

(iii) It is situated inside the integumentbut outside the nucellus.

(iv) It has an egg apparatus, situated atthe chalazal end.

(A) i and iv (B) ii and iii

(C) i and ii (D) ii and iv.

10. Autogamy can occur in a chasmogamousflower if

(A) Pollen matures before maturity of ovule

(B) Ovules mature before maturity ofpollen

(C) Both anther and stigma maturesimultaneously

(D) Both anther and stigma are of equallengths.

11. Choose the correct statements from thefollowing

(A) Cleistogamous flowers always exhibitautogamy

(B) Chasmogamous flowers always exhibitgeitonogamy

(C) Cleistogamous flowers exhibit bothautogamy and geitonogamy

(D) Chasmogamous flowers never exhibitautogamy.

12. A particular species of plant produces light,nonsticky pollen in large numbers and itsstigmas are long and feathery. Thesemodifications facilitate pollination by

(A) Insects (B) Water

(C) Wind (D) Animals.

13. From among the situations given below,choose the one that prevents both autogamyand geitonogamy

(A) Monoecious plant bearing unisexualflowers

(B) Dioecious plant bearing only male orfemale flowers.

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(C) Monoecious plant with bisexual flowers

(D) Dioecious plant with bisexual flowers.

14. In a fertilised embryo sac, the haploid,

diploid and triploid structures are

(A) Synergid, zygote and primary

endosperm nucleus

(B) Synergid, antipodal and polar nuclei

(C) Antipodal, synergid and primary

endosperm nucleus

(D) Synergid, polar nuclei and zygote.

15. In an embryo sac, the cells that degenerate

after fertilisation are

(A) Synergids and primary endosperm cell

(B) Synergids and antipodals

(C) Antipodals and primary endosperm

cell

(D) Egg and antipodals.

16. While planning for an artificial

hybridisation programme involvingdioecious plants, which of the followingsteps would not be relevant.

(A) Bagging of female flower

(B) Dusting of pollen on the stigma

(C) Emasculation

(D) Collection of pollen.

17. In the embryo of a typical dicot and agrass, true homologous structures are

(A) Coleorhiza and coleopltile

(B) Coleoptile and scutellum

(C) Cotyledons and scutellum

(D) Hypocotyl and radicle.

18. The phenomenon observed in some plantswherein parts of the sexual apparatus isused for forming embryos withoutfertilization is called

(A) Parthenocarpy

(B) Apomixis

(C) Vegetative propagation

(D) Sexual reproduction.

19. In a flower, if the megaspore mother cellforms megaspores without undergoingmeiosis and if one of the megasporesdevelops into an embryo sac, its nucleiwould be

(A) Haploid (B) Diploid(C) A few haploid and a few diploid(D) With varying ploidy.

20. The phenomenon wherein, the ovarydevelops into a fruit without fertilizationis called(A) Parthenocarpy (B) Apomixis(C) Asexual reproduction(D) Sexual reproduction.

1. (C) 2. (C) 3. (A) 4. (D) 5. (D) 6. (B) 7. (A) 8. (B) 9. (C) 10. (C)

11. (A) 12. (C) 13. (B) 14. (A) 15. (B) 16. (C) 17. (C) 18. (B) 19. (B) 20. (A)

1. Name the component cells of the ‘‘egg apparatus’’ in an embryo sac.

Ans. One egg (oosphere) and two synergids.

2. Name the part of gynoecium that determines the compatible nature of pollen grain.

Ans. Stigma.

3. Name the common function that cotyledons and nucellus perform.

Ans. Nourishment

4. Complete the flow chart.

Pollen mother cell �� Pollen tetrad �� Pollen grain

..........................

Vegetative cell

��/'�)��%"#('!� #�� )#0�" �&��)��$ �6+Ans. Generative cell.

5. Indicate the stages where meiosis and mitosis occur (1, 2 or 3) in the flow chart.

Megaspore mother cell �

�� Megaspores �

�� Embryo sac �

��Egg.

Ans. 1— Meiosis. 2. — Mitosis.

6. Name the parts of the pistil which develop into fruit and seeds.

Ans. Fruit— Ovary. Seeds— Ovules.

7. In case of polyembryony, if an embryo develops from synergid and another from the nucellus,which is haploid and which is diploid ?

Ans. Embryo developed from syneryid. Haploid.

Embryo developed from nucellus. Diploid.

8. Can an unfertilised, apomictic embryo sac give rise to a diploid embryo ? If yes, then how ?

Ans. Yes. Apomictic embryo developed from diploid embryo sac formed from nucellus or integument willbe diploid.

9. Which are the three cells found in a pollen grain when it is shed at the three celled stage ?

Ans. One tube or vegetative cell and two male gametes.

10. What is self incompatibility ?

Ans. Self incompatibility or self sterility is the inability of the pollen grain of a flower to grow and formfunctional pollen tube on the stigma of the same flower. e.g., crucifers. It is genetically based andis due to occurrence of similar genes of sterility in pollen grains (e.g., S1) and stigma (S1S3).

11. Name the type of pollination in self-incompatible plants.Ans. Cross pollination.

12. Which is the triploid tissue in a fertilised ovule ? How is the triploid condition achieved ?

Ans. Endosperm is the triploid tissue found in a fertilised ovule. The triploid condition is achieved byfusion of two polar nuclei and one nucleus of a male gamete (triple fusion).

13. Are pollination and fertilisation necessary in apomixis ? Give reasons.Ans. No. Apomixis is formation of new individuals through asexual method of development of embryo and

seed without fusion of gametes. In apomixis, embryos directly develop from integument, nucellus,egg or synergid. Pollination and fertilization are not required.

14. Identify the type of pistil with the help of diagram given here.

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Ans. A. Multicarpellary syncarpous.

B. Multicarpellary apocarpous.

�6* ��#�%�� #��, #)#&-�.��15. How is pollination carried out in water plants ?

Ans. Hydrophily or water pollination takes place in many aquatic plants (in emerged flowers anemophilyand entomophily are more common). In epihydrophily, pollination occurs over the surface of water(pollen grains without exine, lighter than water). In hypohydrophily, pollination occurs inside water(pollen grains without exine, with same specific gravity as that of water).

16. What is the function of the two male gametes produced by each pollen grain in angiosperms ?

Ans. (a) One male gamete fuses with egg to perform generative fertilization or syngamy.

(b) Second male gamete fuses with secondary nucleus of central cell to perform vegetative fertilization.

1. List three strategies that bisexual chasmogamous flower can evolve to prevent self pollination(autogamy).

Ans. 1. Dichogamy, either protandry (maturation of anthers earlier than stigma e.g., Salvia) or protogyny(maturation of stigma earlier than anthers, e.g., Mirabilis).

2. Heterostyly or having different heights of styles and stamens, e.g., diheterostyly (e.g., Jasmine),triheterostyly (e.g., Lythrum).

3. Herkogamy or mechanical devices like extrorse anthers, lever mechanism, e.g., Salvia.

2. Given below are events that are observed in an artificial hybridisation programme. Arrangethem in the correct sequential order in which they are followed in the hybridisation programme.

(a) Re-bagging (b) Selection of parents (c) Bagging (d) Dusting of the pollen on stigma(e) Emasculation (f) Collection of pollen from male parent.

Ans. b, e, c, f, d and a.

3. Does self-incompatibility impose any restrictions on autogamy ? Give reasonsand suggest the method of pollination in such plants.

Ans. Yes, self incompatibility does not allow self pollination or autogamy. Selfincompatible or self sterile plants perform cross pollination.

4. In the given diagram, write the names of the parts 1—7, shown with lines.

Ans. 1. Scutellum 2. Coleoptile 3. Plumule 4. Epiblast 5. Radicle 6. Root cap7. Coleorhiza.

5. What is polyembryony and how can it be commercially exploited ?

Ans. Polyembryony is the occurrence of more than one embryo in the same seed. Ithas the potential of retaining all the traits of a hybrid as the polyembryony ismostly apomictic developing from diploid cells like those of nucellus. Apomixisis genetically controlled so that its genes can be introduced in hybrid varietiesto obtain hybrid vigour indefinitely.

6. Are parthenocarpy and apomixis different phenomena ? Discuss theirbenefits.

Ans. Yes.

Differences

S.No. Parthenocarpy Apomixis

1. It is formation of seedless fruits. It is formation of seeds asexually.

2. An embryo is absent. An embryo is formed asexually.

3. It has no role in reproduction. It takes part in reproduction.

Benefits

1. Parthenocarpy is economically important Apomixis can maintain hybrid vigour indefinitely.

since irritant seeds are absent.

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7. Why does the zygote begin to divide only after the division of primary endosperm cell (PEC) ?Ans. For its growth, zygote requires nourishment. It obtains the same from primary endosperm cell in

which it is embedded. Therefore, growth, division and storage of food in primary endosperm cell orformation of endosperm is preequisite to growth and division of zygote.

8. The generative cell of a two-celled pollen divides in the pollen tube but not in a three-celledpollen. Give reasons.

Ans. On division, the generative cell is to form two male gemetes. In 3-celled pollen, the generative cellhas already divided into two male gametes, so that no further division occurs in the pollen tube. Intwo-celled pollen grain, the generative cell descends in the pollen tube anddivides to form two male gametes.

9. In the given figure label the following parts :

male gametes, egg cell, polar nuclei, synergid and pollen tube.

Ans. See Fig. 2.26 A (convert labelling of egg nucleus to egg cell.)

10. In the given figure, the plant bears two different types of flowers marked‘A’ and ‘B’. Identify the types of flowers and state the type of pollinationthat will occur in them.

Ans. See sample paper 2010, question 2.

A — Chasmogamous flowers. Homogamy (autogamy) occurs.

B — Cleistogamous flowers. Cleistogamy (autogamy) occurs.

1. Starting from zygote, draw the diagrams of the different stages of embryo development in a dicot.

Ans. Draw diagrams of Fig. 2.29.

2. What are the possible types of pollinations in chasmogamous flowers ? Give reasons.

Ans. Chasmogamy is the condition of opening of flowers so as to expose both the anthers and the stigmasfor pollination. Depending upon the sequence of maturity and position of anthers and stigmas,pollination is of two types, self pollination and cross pollination.

(a) Self Pollination. It occurs if both anthers and stigmas mature at the same time and the twohappen to come in contact with each other.

(b) Cross Pollination. It occurs if anthers and stigmas mature at different times or they havemechanical devices to prevent self pollination. Cross pollination can take place through differentagencies. (i) Anemophily. By the agency of wind. (ii) Hydrophily. By the agency of water.(iii) Entomophily. By the agency of insects. (iv) Ornithophily. By the agency of birds.

3. With a neat labelled diagram, describe the parts of a mature angiosperm embryo sac. Mentionthe role of synergids.

Ans. See NCERT question 6.

4. Draw a diagram of a microsporangium and label its wall layers. Write briefly the role ofendothecium.

Ans. Draw Fig. 2.4 E.

Role of Endothecium. (i) Protection of sporogenous tissue in younger stages. (ii) Helping in dehiscenceat maturity. For this, the dead endothecial cells contract in the region of their outer thin walls andbecome concave. Endothecium shortens and ruptures the thin-walled stomium to produce two longitudinalslits, one in each anther lobe. In others, local degeneration of endothecium produces apical slits orvalves.

5. Embryo sacs of some apomictic species appear normal but contain diploid cells. Suggest asuitable explanation for the condition.

Ans. Embryo sacs can become diploid only if they are formed from diploid megaspores or directly from

�62 ��#�%�� #��, #)#&-�.��nucellar cells. A diploid megaspore develops only if diploid megaspore mothercell either directly functions as megaspore or undergoes mitosis instead ofmeiosis. All the cells of such an embryo sac are diploid in nature. They cangive rise to functional embryos apomictically.

6. In the diagram given here, show the path of a pollen tube from the pollenon the stigma into the embryo sac. Name the components of egg apparatus.

Ans. (a) Draw pollen tube entering embryo sac with the help of Fig. 2.25.

(b) Components of Embryo Sac. Oosphere or egg (1) and two synergids.

7. Draw the diagram of a mature embryo sac and show its 8-nucleate,7-celled nature. Show the following parts : antipodals, synergids, egg,central cell, polar nuclei.

Ans. See NCERT question 6.

Companion Biology XII - S. Dinesh & Co.

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