Sexual and Asexual Reproduction in Plants

Sexual and Asexual Reproduction in Plants

Sexual Reproduction Asexual Reproduction

Sexual Reproduction • In sexual reproduction male and female cells

(Androecium and Gynoecium), called gametes, unite to form a single cell, called a zygote. This zygote then undergoes cell division, ultimately giving rise to a new plant body. Offspring produced sexually, however, have two parents and so, though they certainly resemble the parents, the offspring are not necessarily identical to them. Consequently, sexual reproduction is a process that increases variation among offspring.

Structure of Flower

REPRODUCTIVE STRUCTURE OF FLOWER

Function Of Components of Flower

Together Functioning Reproductive parts of Flowers

• Carpels : These are the female reproductive organs and are found in the center of the each flower. They consist of a hollow Ovary which contains Ovule. The Ovule contain the female gamete. After fertilization, the ovary will become the fruit, protecting the ovule which becomes the Seed. Above the Ovary there’s a narrow Style which ends in the Stigma. The Pollen grains or Anthers (Androecium) stick to the Stigma during Fertilization.

• Stamens : These are the male reproductive organs and are found in a ring (Whorl) around the Carpels. A Stamen consist of a Stalk (Filaments) bearing an Anther. Each Anther is made of 4 pollen sacs in which pollen grains grow and develop. Pollen grains contain the male gametes.

Together Functioning of Flowers Parts

• Petals : These are arranged in a ring (Whorl) around the Stamens and The Carpels. Some flowers have colored and scented Petals with Nectary at the base which produces sugar nectar to attract insects.

• Calyx : These look like small green and are found in a ring (Whorl) outside the Petals. They protect the flower while it is a bud .

• These two parts does not function in Sexual Reproduction.

Ovary And Ovule role in Reproduction

Pollination

POLLINATION• Pollination is a process by which pollens are transferred

from ‘Anthers’ to the Stigma of a plant or flower, thereby enabling reproduction and fertilization.

Pollination •Biotic Pollination•Abiotic Pollination

Pollination Process

•Self Pollination•Cross Pollination

Biotic And Abiotic Pollination• Biotic Pollination : The process of pollination which

requires pollinators : organisms that carry or over the pollen grains from anther to the Stigma. This is done by insects mostly; but also by vertebrates like Bats, Humans and Birds.

• Abiotic Pollination : It refers to situations where pollination is mediate without involvement of other organisms. Abiotic pollination occurs by wind and sometimes by water in case of aquatic plants.

Self-Pollination• It occurs when pollen from one plant Anther to

the same plant Stigmas or to the other flower s on the same plant. Self Pollination occurs in Monoecious Plants: the flowers on a plant are androecium, other flowers on the same plant have gynoecium also, then its mainly done. Self pollination may include autogamy: where pollen moves to gynoecium part or stigmas of the same flower or Geitonomy: where pollen is transferred to another flower on the same plant.

CROSS-POLLINATIONIt occurs when pollen is transferred to Stigma of another flower of the different

plant. It occurs on Dioecious plants, Protandry, Protogyny and on the plants which are self-incompatible.

• Dioecious Plants: Either have Androecium or Gynoecium, which can’t reproduce unisexually.

• Protandry: Anthers of some flowers mature first. Pollination of immature stigma on the same plant is not possible.

• Protogyny: The stigmas mature first and Anthers are immature.• Self-incompatibility: Pollen tubes doesn’t grow well, so no fertilization takes

place.Cross Pollination is done by pollinators like honeybees, hummingbird, bats,

wasps, other insects etc. The Cross Pollination is sexual but it have individual Androecium(Anthers) and Gynoecium(Stigmas or female part) on different plants.

Process of Fertilization

Asexual Reproduction

• Asexual Reproduction requires only on e parent which means it produce unisexually. It have either Androecium or Gynoecium. Asexual reproduction is a mode of reproduction by which offspring arise from a single organism, and inherit the genes of that parent only. There is no sexual union of gametes. Asexual reproduction generates individuals that are genetically identical to the mother plant.

Budding• Budding is a form of asexual reproduction in which a

new organism develops from an outgrowth or bud due to cell division at one particular site. The new organism remains attached as it grows, separating from the parent organism only when it is mature, leaving behind scar tissue.

• Yeast reproduces by  budding. The small bulb-like projection coming out from the yeast is known as a bud.  It detaches from the parent plant and develops into a new plant.

FRAGMENTATION• Fragmentation or clonal fragmentation in multicellular or colonial

organisms is a form of asexual reproduction or cloning in which an organism is split into fragments. Each of these fragments develop into mature, fully grown individuals that are clones of the original organism.

• The simplest green plants, Algae, reproduce by an asexual method known as fragmentation. In filamentous algae, such as Spirogyra, the filaments accidentally break into many fragments. Each fragment may give rise to a new filament of the algae.

Spore Formation• In some lower plants special reproductive units

called spores, develop asexually on the parent body. The spores are microscopic and covered by protective wall. On reaching a suitable environment they develop into a new plant body, for example, in bread moulds, moss, fern.

Vegetative Propagation• The roots, stems and leaves are the vegetative parts of a

plant. When new plants are produced from these parts, the process is called vegetative propagation or vegetative reproduction.

• Natural Methods:• Many plants reproduce naturally using stems, roots and

leaves.

Natural Method : Root• Some plants such as Asparagus and Sweet potato have

tuberous roots. These roots have adventitious buds which grow into a new plant. Thus they can be used for propagation.

• Sometimes reproduction by roots can be done by cutting the down root hairs and put it into another soil where should be only warm and with plenty of water.

REPRODUCTION BY STEMS• Vegetative propagation through stem is very common in

plants. The underground modification of stem, such as rhizome, in ginger, tuber in potato and bulb in onion  have buds which develop into a new plant and are therefore used to carry out vegetative propagation of the plant in the field.

• The bud make its place itself which grow into the same plant species.

Leaves• Even leaves are used for vegetative propagation

of plants. For example, Bryophyllum leaves have buds on their margin.  These buds grow into small plantlets which on detachment from the mother plant grow into independent plants.

Artificial Methods : Layering• Layering is bending a low growing, flexible stem to the

ground. The method is as follows. Cover part of th stem with soil, leaving the remaining above the soil. Bend the tip into a vertical position and stake in place. The sharp bend induces root, thereby giving rise to a new plant. Example: Jasmine, grapevine, Bougainvillea etc.

• These plants have long bales or stem which cant climb properly, So the bales are put inside the soil which grow into the same plants species.

Cuttings• Many plants are grown through their stem cuttings, for

example, Rose, Croton, Money plants, Sugarcane, etc. Cuttings of these plants can be grown even in water where they strike roots and develop adventitious buds.

• The cutting can be done only when there lot of strength in the stems or leaves.

Grafting• A very common method of artificial propagation is grafting.

It is taking a part from one plant and making it grow on another plant. The method is useful in propagating improved varieties of many flowers and fruits such as rose, bougainvillea, mango, apple, etc.

• In this process a small branch is inserted into a rooted plant. The rooted plant called stock is stronger. In this stock a stem cutting from the desired plant is inserted which is known as scion or graft. The grafted end of stock and scion fit well with each other and are bound firmly with tape or rubber-band until their tissues unite and become one