Biology class 12

8/13/2019 Biology class 12

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Series : SKS/1

Roll No.

Code No. 57/1/1Candidates must write the Code onthe title page of the answer-book.

Code number given on the right hand side of the question paper should be written on the title page of

the answer-book by the candidate.

Please check that this question paper contains 30 questions.

Please write down the Serial Number of the questions before attempting it.

15 minutes time has been allotted to read this question paper. The question paper will be distributed at10.15 a.m. From 10.15 a.m. to 10.30 a.m., the student will read the question paper only and will notwrite any answer on the answer script during this period.

BIOLOGY

[Time allowed : 3 hours] [Maximum marks : 70]

General Instructions:

1. All questions are compulsory.

2. This questions paper consists of four Sections A, B, C and D. Section-A contains 8 questions of one mark each, Section-B is of 10 questions of 2 marks each, Section-C is of 9 questions of threemarks each and Section-D is of 3 questions of five marks each.

3. There is no overall choice. However, an internal choice has been provided in one questions of 2 marks, one questions of 3 marks and one question of 5 marks weightage. A student has toattempt only of the alternatives in such questions.

4. Wherever necessary, the diagrams drawn should be neat and properly labelled.

Studymate Solutions to CBSE Board Examination 2012-2013


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SECTION-A1. An anther with malfunctioning tapetum often fails to produce viable male gametophytes.

Give any one reason. [1]

Ans. Tapetum nourishes the developing pollen grain so a malfunctioning tapetum will fail to produceviable male gamete.

2. Why sharing of injection needles between two individuals is not recommended? [1]

Ans. Sharing of injection needles may lead to transmission of HIV-infection.

3. Name the enzyme and state its property that is responsible for continuous and discontinuousreplication of the two strands of a DNA molecule. [1]

Ans. DNA dependent DNA polymerase. This enzyme catalyse polymerisation only in one direction,i.e., 5' 3'. As a result on template strand with 3' 5' the replication is continuous while onthe template strand with polarity 5' 3' it is discontinuous.

4. Identify the examples of convergent evolution from the following: [1]

(i ) Flippers of penguins and dolphins ( ii ) Eyes of octopus and mammals

(iii ) Vertebrate brains

Ans. (i ) Flippers of penguins and dolphins ( ii ) Eyes of octopus and mammals

5. Write the importance of MOET. [1]

Ans. In MOET cow is given hormones with FSH like activity. These hormones induce follicularmaturation and super-ovulatin which produces 68 eggs per cycle instead of one egg.

6. Why is the enzyme cellulase needed for isolating genetic material from plant cells and notfrom the animal cells? [1]

Ans. Since plant cells have cell wall, so to digest it cellulase is required. Animals do not have cellwall so no cellulase required.

7. Name the type of biodiversity represented by the following: [1]

(a ) 50,000 different strains of rice in India.

(b ) Estuaries and alpine meadows in India.

Ans. (a ) Genetic diversi ty

(b ) Ecological diversity

8. Write the equation that helps in deriving the net primary productivity of an ecosystem. [1]

Ans. GPP R = NPP [where GPP = Gross Primary Productivity, R = Respiratory losses]

SECTION-B9. Geitonogamous flowering plants are genetically autogamous but functionally cross-pollinated.

Justify. [2]

Ans. In Geitonogamous flowers the pollen grain comes from the same plant. It is being transferredto the stigma of another flower fo same plant. So it is functionally cross pollination by involvingpollinating agent but genetically it is autogamy.


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Ans. (i ) PCR - Polymerase Chain Reaction

(ii ) ELISA - Enzyme linked Immuno sorbent Assay.

OR

(a ) Exonuclease - cuts the DNA at free ends.

Endonuclease - cuts within DNA segment

(b ) Resticriction endonuclease, : cuts within the DNA, at specific sites called pallindromicsites.

e.g. Eco R1 cuts the DNA at following pallindromic sequences.

5' G A A3' C T T

T T CA A G 5'

3'

16. Name any two sources of e-Wastes and write two different ways for their disposal. [2]

Ans. Example of e-waste are: Irreparable computes and Electronic goods.

Two different ways for their disposals are

(i ) Buried in landfills.(ii ) Incinerated.

17. Why the pyramid of energy is always upright? Explain. [2]

Ans. Pyramid of energy is upright because when energy flows from a trophic level to next trophiclevel, some energy is always lost as heat at each step. Finally it is lost to atmosphere andnever goes back to Sun.

18. Explain why very small animals are rarely found in polar region. [2]

Ans. Very small animals have large surface area with respect to volume, there is more chanceof heat loss, hence they are rarely found in polar region.

SECTION-C19. Draw a diagram of the microscopic structure of human sperm. Label the following parts in it

and write their functions. [3]

(a ) Acrosome ( b ) Nucleus

(c ) Middle piece

Ans.


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20. With the help of any two suitable examples explain the effect of anthropogenic actions onorganic evolution. [3]

Ans. Effect of anthropogenic actions on organic evolutions.

(i ) Industial melanism: It was due to smoke and soot coming out of man made industrieswhich caused a shift from white-winged moths on trees to dark winged or melanisedmoths.

Prior to industrialisation white coloured lichens covered the bark of trees which wasfavourable for white winged moths.

(ii ) Use of herbicides and pesticides has resulted in selection of resistant varieties in very short time scale. Also development of microbes resistant to antibiotics in period of months is due to anthropogenic actions.

21. (a ) Why is human ABO blood group gene considered a good example of multiple alleles? [3]

(b ) Work out a cross up to F 1 generation only, between a mother with blood group A(Homozygous) and the father with blood group B (Homozygous). Explain the pattern of inheritance exhibited.

Ans. (a ) ABO blood group is controlled by I gene.

I genes has 3 alleles IA

, IB

, i Therefore ABO blood group is a good example of multiple allelism

(b ) Genotype I IA A I IB B(Mother) (Father)

I IA B

Progeny will have blood group AB.

This shows codominance pattern of inheritance.

22. Describe the structure of a RNA polynuclotide chain having four different types of nucleotides.[3]

Ans. RNA polynucleotide consists of namely

(i ) Sugar = Ribose ( ii ) Phosphate group

(iii ) Nitrogenous bases like

Adenine - A Uracil - U

Cytosine - C Guanine - G

23. Differentiate beteen inbreeding and outbreeding in cattle. State one advantage and onedisadvantage for each one of them. [3]

Ans. SN Inbreeding Outbreeding

1. Mating of more closely relatedindividuals

Mating of unrelated animals

2. Mating is between animals of samebreed for 4-6 generations

If mating is between animals of same breedthem there should be no common ancestorfor 4-6 generations.

4. Mating is between same species. Mating can be between different species.


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Advantage of inbreeding

It increases homozygosity so is used for developing pure lines.

Advantage of out breeding

It produces hybrids with desirable characters like better lactation period and high milkproductions.

24. (a ) Why are the fruit juices bought from market clearer as compared to those made athome? [3]

(b ) Name the bioactive molecules produced by Trichoderma polysporum and Monascus purpureus .

Ans. (a ) Fruit juices bought from market are clearer as compared to home because bottled juicesare clarified by the use of poctinases and proteases.

(b ) Trichoderma polysporum produces Cyclosporin A.

Monosacus purpurens produces statins.

25. (a ) Why are transgenic animals so called? [3]

(b ) Explain the role of transgenic animals in

(i ) Vaccine safety ( ii ) Biological products

with the help of an example each.

Ans. (a ) Transgenic animals are so called because they have their DNA manipulated. As aresult they possess and express foreign gene.

(b ) Role of in vaccine safety

Transgenic mice are being used to test the safety of the polio vaccine before they areused on humans.

Biological products

Medicines required to treat many human diseases contain certain biological productswhich are expensive to make. These products can be produced by transgenic animalsby induction of genes in them which code for particular product e.g. human protein ( -1 - antitrypsin)

26. How have human activities caused desertification? Explain. [3]

OR

How does algal bloom destroy the quality of a fresh water body? Explain. [3]

Ans. The development of the fertile top soil takes centuries. But it can be removed very easily dueto human activities like over- cultivation, unrestricted grazing, deforestation and poorirrigation practices, resulting in arid patches of land. When large barren patches extend andmeet over time, a desert is created. Now-a-days, desertification is a major problem particulary due to increased urbanisation.

OR

Ans. Presence of large amounts of nutrients in water causes excessive growth of planktonic (free-floating) algae, called an algal bloom which imparts a distinct colour to the water bodies. Algalblooms cause deterioration of the water quality and fish mortality. Some bloom forming algalare extremely toxic to human beings and animals.


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(b ) Characteristics of wind pollinated flowers:

(i ) Large number of pollen grains are produced.

(ii ) Pollen grains are light and non-sticky.

(iii ) Well exposed stamens so that pollen grain are easily dispersed.

(iv ) Large and feathery stigma to trap pollen grains.

OR

Ans. (a )

(b ) Changes hapenning in ovary and uterus during menstrual cycle are caused by changein the levels of pituitary and ovarian hormones.

After menstrual phase gonadotropin i.e. , Luteinising hormone (LH) and follicularstimulating hormone (FSH) are released from pituitary . Their level gradually increasesduring follicular phase and it stimulates development of follicles and secretion of estrogen by growing follicles.

Both LH and FSH attain peak on 13th & 14th day.

Rapid secretion LH causes ovulation on day 14.

During luteal phases Graafian follicle changes to corpus luteum which secretesProgesterone Progesterone maintains endometrium which is necessary forimplantation .

29. Describe the asexual and sexual phases of life cycle of Plasmodium that causes malaria inhumans. [5]

OR

(a) What is plant breeding? List the two steps the classical plant breeding involves.

(b) How has the mutation breeding helpes in improving crop varieties? Give one example

where this technique has helped.(c) How has the breeding programme helped in improving the public nutritional health?

State two examples in support of your answer.


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Ans.

OR

Ans. (a ) Plant breeding : It is manipulation of plant species so as to produce plants with desiredcharacters like better yield and disease resistance.

Classical plant breeding involves

(i ) Hybridisation of pure lines.

(ii ) Artificial selection for producing plant with desired characters of higher yield orresistance to diseases.

(b ) Mutational breeding - creates genetic variations through changes in the basesequences within genes. This results in new character which is not found in parents.

Improved varieties can be produced by inducing mutations artificially in the plantshaving desirable characters.

For example in mung bean resistance to yellow mosaic virus and powdery mildew wasinduced by limitations.

(c ) Breeding crops with higher levels of vitamins and minerals or higher proteins andhealthier fats has improved public health.


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Breeding programmes have been designed with objectives of

(i ) improved protein content and quality.

(ii ) Oil content and quality

(iii ) Vitamin content

(iv ) Micronutrients and mineral contains

maize hybrids having double amount of lysine and tryopophan have been developed.Similarly IARI New Delhi have developed many vegetable crops rich in vitaminsand minerals like spinach, carrots, pumpkin etc.

30. A child by the family from Thalassemia is born to a normal couple. But the mother is beingblamed by the family for delivering a sick baby. [5]

(a) What is Thalassemia?

(b) How would you counsel the family not to blame the mother for delivering a child sufferingfrom this disease? Explain.

(c) List the values your counselling can propagate in the families.

Ans. (a ) Thalassemia - is an autosomal reccessive blood disease which can occur due to deletionof the genes controllign the formation of globin chains (commonly and ) of haemoglobin.

(b ) Mother cannot be blamed for the disease as, it is an autosomal reccessive blood disorder.

The genes for the synthesis of globin chains are present on autosomes i.e.

(i ) Formation of chain is controlled by 2 genes present on chromosome 16 and

(ii ) Formation of -chain is controlled by one gene present on chromosome 11manifestation of the disease occurs when the progeny receives defective genesfrom both the parents (as thalassaemia is expressed is homozygous recessivecondition only).

(c ) Values that can be propogated in families are

(i ) One should be aware of such autosomal diseases ad should get themselves checkedfor the same before marriage.

(ii ) Manifestation of the disease occurs due to defective genetic set up of both theparent (so it is not only mother to be blamed.


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SECTION-A5. Identify the examples of homologous structures from the following.

(i ) Vertebrate hearts

(ii ) Thorns in Bougainvillea and tendrils of Cucurbita

(iii ) Food storage organs in sweet potato and potato.

Ans. (i) and (ii)

9. Describe the gene therapy procedure for an ADA-deficient patient.Ans. In gene therapy, lymphocytes from the blood of patient are grown in a culture ouside the

body. A functional ADA CDNA (using reteroviral vector) is then introduced into theselymphocytes which are subsequently returned to the patient.

However as these cells are not immortal, patient requires periodic infusions of suchgenetically engineered lymphocytes.

14. (a ) How does cleistogamy ensure autogamy?

(b ) State one advantage and one disadvantage of cleistogamy to the plant.

Ans. (a ) Cleistogamy ensures autogamy as cleistogamous flowers do not open at all and hencethere is no chance of cross pollination as there is no chance of cross-pollen landing onthe stigma.

(b ) Advantage

Clestogamous flowers produce assured seed set even is absence of pollinators.

Disadvantage

No variation is there in the progeny.

15. When and where do chorionic villi appear in humans? State their function.

Ans. Chorionic villi appear

1. After implantation

2. On trophoblast.

Function : The chorion villi and uterine tissue become interdigitated with each other and join to form, a structural and functional unit betwwen developing embryo (foetus and maternalbody called placenta).

18. (a ) Explain how to find whether an E.coli bacterium has transformed or not when arecombinant DNA bearing amplicillin resistant gene is transferred into it.

(b ) What does the amplicilling resistant gene act as in the above case?

Ans. (a ) If E. Coli has been transformed then these transformed E.coli cells would be able togrew on ampicillin medium.

(b ) Ampicillin resistant gene acts as a selectable marker in this case.

Code No. 57/1/2

Studymate Solutions to CBSE Board Examination 2012-2013

UNCOMMON QUESTIONS ONLY

Series : SKS/1


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SECTION-C22. (a ) Explain how to overcome inbreeding depression in cattle.

(b ) List three advantages of inbreeding in ctalle.(c ) Name an improved breed of cattle.

Ans. (a ) Inbreeding depression in Cattle is overcomed by mating the selected animals of breedingpopulation with unrelated superior animals of same breed, to restore fertility and yield.

(b ) Advantages of Inbreeding in Cattle:(i ) Helps in evolving a pureline in any animal.(ii ) It exposes harmful recessive genes that are eliminated by selection.(iii ) Helps in accumulation of superior genes.

(c ) Improved variety of Cattle is Hisardale a new breed of sheep developed by crossingBikaneri ewes and Marino rams.

27. (a ) Draw a diagram of the structure of a human ovum surrounded by corona radiata. Labelthe following parts:

(b ) (i ) Ovum(ii ) Plasma Membrane(iii ) Zona Pellucida

Ans. (a )

Ovum

Plasma membrane

Zonapellucida

(b ) Function of Zona Pellucida

It completely surrounds the ovum and prevents polyspermy.

SECTION-D

30. (a ) Draw a labelled schematic diagram of the transverse section of a mature anther of anangiosperm plant.

(b ) Describe the characteristic features of an insect pollinated flower.

OR

(a ) Describe the events of spermatogenesis with the help of a schematic representation.

(b ) Write two differences between spermatogenesis and oogenesis.

Ans. (a )


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(b ) Majority of Insect pollinated flowers are

1. Large

2. Colourful

3. Fragnant

4. Rich in nectar

5. Flowers pollinated by flies and beettles secrete foul odours to attract them.OR

Ans. (a )

(i ) Spermatogenesis starts at the age of puberty

(ii ) Spermatogonia are present on the inside wall of semniferous tubules multiply by

mitotic divisions and increase in numbers.(iii ) Each spermatogonium is diploid and contain 46 chromosomes

(iv ) Some of spermatogomia called primary spermato cytes undergo meiosis I toproduce 2 equal haploid cells called - secondary spermatocytes with 23chromosomes each

(v ) Secondary spermatocyte undergo second meiotic division to produce 4 equalhaploid spermatids.

(vi ) Spermatid later transform into spermatozoa.

(b ) Spermatogenesis Oogenesis

(i ) It occurs in testes It occurs in ovaries

(ii ) A spermato gonium forms 4 spermatozoa An oogonium forms one ovum


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21. (a ) Differentiate between inbreeding and outbreeding.

(b ) Explain inbreeding depression and how it can be overcome.

(c ) Mention two advantages of inbreeding programme in cattle.

Ans. (a ) When breeding is between animals of the same breed it is called inbreeding.

when crosses between different breeds are called outbreeding.

(b ) Inbreeding exposes harmful recessive genes that are eliminated by selection. It alsohelps in accumulation of superior genes and elimination of less desirable genes. thereforethis approach where there is selection at each step, increases the productivity of inbredpopulation. However, continued inbreeding, expecially close inbreeding usually reducesfertility and even productivity. This is called inbreeding dipression.

(c ) Two advantages of inbreeding programme in cattle are

(i ) In breeding increases homozygosity.

(ii ) A superior female, in the case of cattle is the cow or buffalo hthat produces moremilk per lactation, it also helps in accumulation of superior genes and eliminationof less desirable gens.

SECTION-D29. (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.

OR

(a ) Describe the events of Oogenesis with the help of schematic representation.

(b ) Write two differences between Oogenesis and Spermatogenesis.

Ans. (a )

(b ) During fertilization, 1 st male gamete fuses with the egg cell and forms the diploidzygote, while the second male gamete fuses with the polarnuclei forms the triploidendosperm.

(n ) + ( n ) 2n Diploid Zygote 1 st male Egg Cell gamete

(n ) + (2 n ) 3n Triploid endosperm 2 nd male Central Cell

gamete having the polar nuclei


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OR

Ans. (a )

The process of formation of a nature female gamete is called oogenesis, which isdifferent from spermatogenesis. Oogenesis is initiated during the embryonicdevelopment stage when a couple of million gamete mother cells (oogonia) areformed within each fetal ovary, no more oogonia are formed and added after birth.

These cells start division and enter into prophase 1 of the meiotic division and gettemporarily arrested of the stage, called primary oocytes. Each primary oocyte thengets surrounded by a layer of granulosa cells and then called the primary follicle.

The primary follicles get surrounded by more layers of granulose cells and a newtheca and called secondary follicle which is characterized by a fluid filled cavity called antrum. Primary oocyte within the tertiary called antrum. Primary oocytewithin the tertiary follicle grows in size and completes its first meiotic division. It

is an unequal division resulting in the formation of a large haploid secondary oocyteand a tiny first polar body. The tertiary follicle further changes into the maturefollicle or graffian follicle. Graffian follicle now ruptures to release the secondary oocyte (ovum) from the ovary by the process called ovulation.

Biology class 12

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