Biology - Class Twelve
REPRODUCTION IN ORGANISMS
Topics covered in this chapter of Reproduction in Organism
1. Reproduction 2.Types of Reproduction 3.Vegetative Propagation 4.Gametogeneis 5.Fertilisation 6.Embryogenesis 7.Sexuality in organisms
Reproduction:
The biological process through which an organism gives rise to offspring similar to itself is called reproduction. Reproduction facilitates continuity of the species; generation after generation. The mechanism of reproduction depends on an organism’s habitat, internal physiology and several other factors.
Types of Reproduction:
There are two main types of reproduction -
(1) Asexual and
(2) Sexual reproduction.
(1)Asexual Reproduction:
When a single parent is involved in reproduction and there is no gamete formation, this type of reproduction is called asexual reproduction.
Offspring produced through asexual reproduction are identical and are exact copies of their parent. Since offspring are morphologically and genetically similar to their parent, hence they are also called clones of their parent.
Asexual reproduction is common among unicellular organisms. It is also common among plants and animals with relatively simple organization. Some methods of asexual reproduction are as follows:
(a) Binary Fission:
This method is quite common among unicellular organisms. The mother cell undergoes mitosis to produce two daughter cells. The parent generation ceases to exist after binary fission. Example: amoeba, paramecium, bacteria, etc.
(b) Budding:
This method is seen in unicellular fungus, i.e. yeast. This is also seen in hydra. A small bud grows from the mother cell of yeast. The bud grows to a certain size and gets detached. After that, the bud grows to become an adult.
(c) Multiple Fission:
In this method, the nucleus of the mother cell divides into numerous nuclei. The mother cell gets covered with a hard coating; called cyst. The cyst helps the daughter nuclei to tide over unfavourable circumstances. When the favourable circumstances return, the cyst ruptures and releases the daughter nuclei. Each daughter nucleus subsequently develops into an adult. Example: Plasmodium, paramecium, etc.
(d) Spore Formation:
Some organisms produce spores in special spore-bearing organs. Spores are considered to be precursors of seeds in plants. Spores help an organism to tide over the unfavourable conditions. Examples: some fungi and algae.
(e) Vegetative Propagation:
Most of the flowering plants reproduce sexually, but many of them also have the capability to produce a new plant through their vegetative parts; such as roots, stems and leaves. When a new plant is formed from vegetative part, this is called vegetative propagation. Example: rose, banana, sugarcane, sweet potato, potato, etc.