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Reproduction in Animal
- There are two modes by which animals reproduce. These are:
- Sexual reproduction, and
- Asexual reproduction.
- There are many organisms which do not reproduce (mules, sterile worker bees, infertile human couples, etc.).
- The reproductive parts in animals produce gametes that fuse to form a zygote.
- It is the zygote which develops into a new individual. This type of reproduction beginning from the fusion of male & female gametes is called sexual reproduction.
- The male reproductive organs include a pair of testes (singular, testis), two sperm ducts & a penis. The testes produce the male gametes called sperms.
- The female reproductive organs are a pair of ovaries, oviducts (fallopian tubes) & the uterus. The ovary produces female gametes called ova (eggs).
- In human beings, a single matured egg is released into the oviduct by one of the ovaries every month.
- The uterus is the part where the development of the baby takes place.
- Like the sperm, an egg is also a single cell (haploid cell).
- The first step in the process of reproduction is the fusion of a sperm & an ovum.
- When sperms come in contact with an egg, one of the sperms may fuse with the egg. Such fusion of the egg & the sperm is called fertilization.
Internal & External Fertilization
- During fertilization, the nuclei of the sperm & the egg fuse to form a single nucleus.
- This results in the formation of a fertilized egg or zygote.
- Fertilization which takes place inside the female body is called internal fertilization.
- Internal fertilization occurs in many animals including humans, cows, dogs & hens.
- During spring or rainy season, frogs & toads move to ponds & slow flowing streams. When the male & female come together in water, the female lays hundreds of eggs.
- Unlike hen’s egg, frog’s egg is not covered by a shell & it is comparatively very delicate.
- A layer of jelly holds the eggs together & provides protection to the eggs.
- As the eggs are laid, the male deposits sperms over them. Each sperm swims randomly in water with the help of its long tail. The sperms come in contact with the eggs. This results in fertilization.
- This type of fertilization in which the fusion of a male & a female gamete takes place outside the body of the female is called external fertilization.
- It is very common in aquatic animals such as fish, starfish, etc.
- In each hydra, there may be one or more bulges.
- These bulges are the developing new individuals & they are called buds.
- In Hydra, the new individuals develop as outgrowths from a single parent.
- This type of reproduction in which only a single parent is involved is called asexual reproduction.
- Since new individuals develop from the buds in hydra, this type of asexual reproduction is called budding.
- Another method of asexual reproduction is observed in the microscopic organism, amoeba.
- Reproduction in which an animal reproduces by dividing into two individuals is called binary fission.
- Apart from budding & binary fission, there are other methods by which a single parent reproduces the young ones.