- Reproduction is the biological process by which new individual organisms are produced.
- There are two basic types of reproductions namely asexual and sexual.
- Asexual reproduction is a process in which the organism reproduces on its own without the help of another individual. There is only single parent.
- Sexual reproduction is a process in which two parents, a male and a female, are needed to produce a new individual.
2. Reproduction in animals:
- In most animals, two individuals- a male and a female – are needed for reproduction, therefore the reproduction is sexual.
- Each individual or parent produces a special sex cell known as gamete. In animals, the gamete produced by the female is called the egg or ovum, and that produced by the male is called the sperm.
- When the sperm and ovum fuse together, they form the zygote. This is the first cell of the new organism. This process of fusion of a male gamete and a female gamete to form a zygote is called fertilization.
- The zygote undergoes cellular division and develops into an embryo. The embryo eventually develops into a new individual.
- In animals such as frogs, fishes, birds, reptiles and humans, an individual carries only one kind of gamete- either sperm (in the male) or the ovum (in the females). However, some organisms produce both male and female gametes in the same body. Such organisms are called hermaphrodites. Snail, slug, leech and earthworm are examples of hermaphrodites.
Types of fertilization:
There are various methods by which fertilization takes place in the living world:
- External fertilization is the process of fertilization in which fusion of the gametes takes place outside the body of the organisms.
- In most aquatic animals, such as bony fish, the male and female release their sperms and eggs into the surrounding water. The sperms swim to the eggs and fertilize them. This fertilization takes place outside the parent’s body.
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- Internal fertilization is the process of fertilization in which fusion of the gametes takes place inside the body of the organisms.
- In organisms like reptiles, birds and mammals that usually live on land, sperms are released directly into the body of the female since the sperms would be unable to move on land. The males and females mate, and the sperms enter the female body where they fertilize the eggs.