Question

Explain plant reproduction including sexual and asexual. Be sure to include flowers, fruit, different types of propagation and seed dispersal.

Answer 1

Reproduction is a process by which an organism is able to propagate itself and give rise to progenies.

Plants are green photosynthetic organisms which are capable of showing both sexual and asexual reproduction.

Sexual reproduction is characterized by the formation and fusion of gametes from two different parents where as asexual reproduction do not show formation and fusion of gametes.

Two parents are involved in sexual reproduction where only one parent is involved in asexual reproduction.

Genetic recombination takes place in sexual reproduction whereas no such phenomena is observed in asexual reproduction.

Progenies are different from the parent and also from one another in sexual reproduction whereas progenies are identical in asexual reproduction.

Sexual reproduction gives rise to few progenies at one time whereas a large number of progenies can be obtained in asexual reproduction.

Sexual reproduction is carried out under favourable conditions where as asexual reproduction is more a means of perennation during unfavourable condition.

These were the general characteristics of both sexual and asexual reproduction. Now we will look at both the processes in detail.

Sexual reproduction in flowering plants

A plant includes leaves, stem and roots as its vegetative body whereas the flower is a reproductive structure.

A flower is made up of four whorls, androecium and gynoecium are the reproductive whorls whereas sepals and petals are the accessory whorls.

Sepals and petals are not involved in production but help to attract pollinator and protect the reproductive parts of the flower.

Androecium is the male reproductive part and consists of anther and filament. Anther contains pollen grain which inside female gametophyte give rise to two sperm cells.

Gynoecium is the female reproductive part and consists of stigma, style and ovary. Stigma is the surface where pollen grains plants and ovary contains the ovules. Style is the structure which connects stigma to ovary.

Sperm and ovum fuse to form a diploid zygote. This process is called as syngamy. Zygote is a single cell structure. It undergoes mitosis to form embryo and then an adult plant body.

The two polar nuclei present in the female gametophyte fuse with other sperm cell to form a triploid endosperm. It is a nutritive tissue for the developing embryo.

After the fertilization, ovary forms the fruit and ovule forms the seed. Seed is a structure which is covered by a tough protective layer and inside it embryo is present. Seeds have the ability to disperse far off places by biotic and abiotic pollinator and give rise to new plants there. The most important significance of seed is that it ensures continuation of generation. Seed have the ability to tolerate unfavourable conditions even for thousands of years and then also remain viable. On the return of favourable conditions, they germinate to give rise to a new plant body.

Asexual reproduction in flowering plants

Asexual reproduction in lower plants like bryophytes and pteridophytes occurs by the formation of spores.

In flowering plants, It is seen by the the presence of different structures like corm, tubers, stolon, rhizome, etc.

Corm is seen in Crocus, tubers in potato and sweet potato, rhizome in ginger and turmeric.

The most important mode of asexual reproduction is apomixis. Apomixis refers to the development of progenies without formation and fusion of gametes. In this type of reproduction, the female parent is capable of giving rise to the zygote directly. This is also called as parthenogenesis.

Zygote can be formed directly from the female gametophyte from the cells other than the egg cell. The female gametophyte consists of synergids, Polar nuclei and antipodals. Any one of these cells are capable of giving rise to zygote without fertilization.

See the structure of female gametophyte or embryo sac below -

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