CBSE Class 8 Science • Chapter 14 • Detailed Master Notes
Chapter Overview
Reproduction is essential for the continuation of a species. It ensures the continuity of similar kinds of individuals, generation after generation. In this chapter, we will learn how reproduction takes place in animals.
Just like plants, animals reproduce in two main ways:
Reproduction beginning from the fusion of male and female gametes is called sexual reproduction.
The male reproductive organs include a pair of testes (singular: testis), two sperm ducts, and a penis. The testes produce the male gametes called sperms. Millions of sperms are produced. Though they are very small, each has a head, a middle piece, and a tail. Every sperm is a single cell with all the usual cell components.
The female reproductive organs are a pair of ovaries, oviducts (fallopian tubes), and 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 development of the baby takes place. An egg is also a single cell.
AI Image Prompt: A scientific illustration showing fertilization. Multiple small tadpole-like sperms with a distinct head and tail are swimming towards and attaching to a single, large round female egg cell. Simple white background with clear structure.
The first step in the process of reproduction is the fusion of a sperm and an ovum. When sperms contact an egg, one of the sperms may fuse with the egg. Such fusion of the egg and the sperm is called fertilization.
Zygote: During fertilization, the nuclei of the sperm and the egg fuse to form a single nucleus. This results in the formation of a fertilized egg or zygote. The zygote is the beginning of a new individual.
The process of fertilization involves the meeting of an egg cell from the mother and a sperm cell from the father. So, the new individual inherits some characteristics from the mother and some from the father.
The zygote divides repeatedly to give rise to a ball of cells. The cells then form groups that develop into different tissues and organs of the body. This developing structure is termed an embryo.
The embryo gets embedded in the wall of the uterus for further development. It continues to develop and forms body parts such as hands, legs, head, eyes, and ears. The stage of the embryo in which all body parts can be identified is called a foetus. When the development of the foetus is complete, the mother gives birth to the baby.
| Category | Definition | Examples |
|---|---|---|
| Viviparous Animals | Animals which give birth to young ones. | Humans, dogs, cows, cats. |
| Oviparous Animals | Animals which lay eggs. The development of the embryo takes place outside the female body inside an egg shell. | Frogs, lizards, butterflies, hens, crows. |
The type of reproduction in which only a single parent is involved is called asexual reproduction.
In Hydra, there may be one or more bulges. These bulges are the developing new individuals and they are called buds. The new individuals develop as outgrowths from a single parent. This type of asexual reproduction is called budding.
Amoeba is a single-celled organism. It reproduces by dividing into two individuals. The process begins with the division of its nucleus into two nuclei. This is followed by division of its body into two, each part receiving a nucleus. Two amoebae are produced from one parent. This is called binary fission.
AI Image Prompt: A diagram showing binary fission in amoeba. Starting with one irregular-shaped parent amoeba at the top, followed by the nucleus elongating and splitting, and finally pinching off into two identical daughter amoebae at the bottom. Clean educational style.
Q1. What is the difference between a zygote and a foetus?
Ans: A zygote is formed by the fusion of male and female gametes; it is a single cell. A foetus is a multicellular stage of the embryo where all main body parts and organs can be identified. It develops from the division of the zygote.