CHAPTER 5 REPRODUCTION IN ANIMALS
The process of reproduction is producing young ones of the species. Reproducing is important for the continuation of a species.
MODES OF REPRODUCTION
(i) Sexual reproduction
When reproduction occurs from the fusion of male and female gametes is called sexual reproduction.
Male reproductive organs:
Male reproductive organs include a pair of testes, two sperm ducts and a penis. The male gametes are called sperms and are produced by testes. A sperm is a single cell. It has a head, a middle piece and a tail.
Female reproductive organs:
Female reproductive organs are a pair of ovaries, oviducts (fallopian tubes) and uterus. The female gametes are called ova or eggs. Eggs are also single celled.
When sperms come in contact with an egg, one of the sperms fuses with the egg and this process is called fertilization during which the nuclei of both the egg and the sperm fuse together to form a single nucleus. This fertilized egg is called a zygote. Since the fertilization takes place inside the body of a female, it is called internal fertilization.
Sometimes fertilization may take place outside the female body. This is called external fertilization.
Development of embryo:
When the zygote divides repeatedly, it gives rise to a ball of cells which then begin to form group of cells which develop into different tissues and organs of the body. This structure is called an embryo.
When the embryo matures a little more, its body parts can be identified. This stage is called the foetus.
Viviparous and oviparous animal:
The animals which give birth to their young ones are called viviparous animals and the animals which lay eggs are called oviparous animals.
(ii) Asexual reproduction
The type of reproduction that involves only one parent is called asexual reproduction. In this type of reproduction, an animal divides into two individuals. This process is called binary fission.
In hydra, new individuals develop from buds and this process is called budding.
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