Reproduction in Organisms

REPRODUCTION

Reproduction is one of the basic characteristics of life. It is the process by which living organisms produce young ones of their own kind, to perpetuate their identity. There are two basic methods of reproduction in living organisms namely Sexual Reproduction and Asexual Reproduction. The method of reproduction that involves the formation and fusion of sex cells (male & female gametes) is called Sexual Reproduction. The process of development of gametes is called Gametogenesis. The process of fusion of male and female gametes is called Fertilization. The method of reproduction that does not involve the formation and fusion of male and gametes is called Asexual Reproduction. Since the young ones are produced from a single parent Asexual Reproduction is also called Uni-parental Reproduction.

1. Reproduction in Plants

There are three different methods of reproduction in plants:

1. Asexual reproduction
2. Vegetative reproduction
3. Sexual reproduction

1. Asexual reproduction in Plants:

It is the main method of reproduction in non-flowering plants like Algae, Bryophytes and Pteridophytes (Ferns). The main method of asexual reproduction in such lower plants is spore formation.

Spore formation in ferns.

2. Vegetative propagation in Plants:

Vegetative propagation is the method of reproduction in which new plants are produced from any part of the plant like root, stem or leaf etc. other than the flower.

3. Sexual Reproduction in Plants:

   Flowering plants (Angiosperms) produce flowers containing stamens and carpels, the male and female reproductive organs respectively. Pollination is the pre-requisite for fertilization in higher plants.

Sexual reproduction is the main method of reproduction in higher plants and is carried out by the flower. Most flowers contain both the male and female reproductive structures in them and are called bisexual flowers. Stamens are the male reproductive organs while carpels are the female reproductive organs. Each stamen has a filament and an anther in its tip. Pollen grains are formed with in the anther. Pistil (carpels) is the female reproductive organ composed of carpels has a basal swollen part called Ovary, a long tubular structure called Style and a knob like tip called the Stigma.The male gamete is a cell in the pollen grain. The female gamete is an egg cell in the ovule. The process that brings the male gamete within reach of the female gamete (i.e. from stamen to stigma) is called pollination. The pollen grain grows a microscopic tube, which carries the male gamete the last few millimeters to reach the female gamete for fertilization. The zygote then grows to form the seed.

Life cycle showing the sexual reproduction in a flowering plant

1. Reproduction in animals

There are two basic methods of reproduction in animals namely Asexual Reproduction and Sexual Reproduction.

Methods of Asexual Reproduction in Animals:

1. Regeneration:

The body of Simple animals like Hydra and Planaria when cut into pieces, each fragment   develops into a complete animal. This   process is called regeneration.

• Parthenogenesis

Parthenogenesis is a phenomenon in which the female gametes (eggs) develop into young ones without fertilization. Parthenogenesis occurs in some fishes, several kinds of insects, and a few species of lizards. Reproduction by parthenogenesis is more rapid that sexual reproduction, and the use of this mode of asexual reproduction permit the animals to quickly exploit the available resources.

• Budding:

It is the method of reproduction in which the young one is produced as an outgrowth (protuberance) or bud from the parent’s body. Eg: Hydra. The bud may later separate from the parent body and becomes a new individual or grow remaining attached to the parent, leading to the formation of a colony.

Sexual Reproduction in Animals

 In higher animals   the sexes are separate like in any mammals. The reproductive   organs that produce gametes are called gonads. The gonad that produces the male gametes (sperms) is called Testis. The gonad that produces the female gametes (ova) is called Ovary. The male gametes are the sperm (or spermatozoa) and the female gametes are the ova (singular = ovum) or eggs. The reproductive union of male and female individuals in which male gametes are transferred into the female’s reproductive tract is called Copulation.

The fusion of sperm and the ovum is called fertilization. The cell formed due to the fertilization of an ovum by a sperm is called a zygote. The zygote will grow by cell division(mitosis) to produce a multicellular structure called embryo which later develops into a new individual.

            Differences between sexual and asexual reproduction