Science Chapter 9

Reproduction in animals

NCERT Solutions for Class 8 Science Chapter 9 are given below.

1. Explain the importance of reproduction in organisms.

Answer: Reproduction is essential for the continuation of a species. If organisms didn’t reproduce, their species would become extinct.

2. Describe the process of fertilization in human beings.

In human beings fertilization occurs when sperms released by the testes of the male come in contact with the ova (egg) released by the ovaries of the female. The egg gets fertilized when one of the sperms fuse with it. During fertilization, the nuclei of the sperm and the nuclei of the egg fuse to form a single nucleus. This process results in the formation of a fertilized egg or zygote. It is this zygote that grows into a new individual.

3. Choose the most appropriate answer.

a) Internal fertilization occurs

(i) in female body

(ii) outside female body

(iii) in male body

(iv) outside male body

Answer: in female body

(b) A tadpole develops into an adult frog by the process of

(i) fertilization

(ii) metamorphosis

(iii) embedding

(iv) budding

Answer: metamorphosis

c) The number of nuclei present in a zygote is

(i) none

(ii) one

(iii) two

(iv) four

Answer: one

4. State whether the following sentences are true or false.

(a) Oviparous animals give birth to young ones – false (The word ‘ova’ means egg. Oviparous animals lay eggs.)

(b) Each sperm is a single cell – true (Each egg is also a single cell)

(c) External fertilization takes place in frogs – true (External fertilization also takes place in some fish, starfish etc.)

(d) A new human individual develops from a cell called gamete – false (A gamete is the cell produced by the reproductive organs of males and females. That means the sperm and the egg are gametes. The male gamete and the female gamete have to fuse to form a zygote. The new individual develops from this zygote.)

(e) Egg laid after fertilization is made up of a single cell – false (The egg is formed when the zygote divides repeatedly and travels down the oviduct. It consists of several cells. An unfertilized egg is a single cell.)

(f) Amoeba reproduces by budding – false (Amoeba reproduces through binary fission; budding is present in hydra.)

(g) Fertilization is necessary even in asexual reproduction – false (In asexual reproduction only a single parent is involved)

(h) Binary fission is a method of asexual reproduction – true

(i) A zygote is formed as a result of fertilization – true

(j) An embryo is made up of a single cell – false (The zygote divides repeatedly to produce a ball of cells. These cells develop into various tissues and organs. This developing structure is called the embryo.)

5. Give two differences between a zygote and foetus.

Answer:

Zygote	Foetus
The zygote consists of just one cell and one nucleus.	The foetus has numerous cells.
The zygote is the rudimentary form of the embryo. It does not have any body parts.	The foetus is a well-developed embryo. Its body parts can be identified easily.

More information: The zygote or the fertilized egg is formed when the nucleus of the sperm fuses with the nucleus of the egg. The zygote consists of just one nucleus. This zygote then divides repeatedly to form a ball of cells which grows into an embryo. As the embryo develops in the uterus it forms various body parts like hands, legs, ears, eyes etc. The embryo becomes a foetus when all of its body parts can be identified.

6. Define asexual reproduction. Describe two methods of asexual reproduction in animals.

Answer: The type of reproduction in which only a single parent is involved is called asexual reproduction. There are mainly two types of asexual reproduction – budding and binary fission. In budding new individuals develop from the buds in the body of the parent. This is present in hydra. In binary fission, an organism reproduces by dividing into two organisms. This method is present in amoeba.

7. In which female organ does the embryo get embedded?

Answer: The embryo gets embedded in the wall of the uterus for further development

8. What is metamorphosis? Give examples.

Answer: The transformation of a larva into an adult through drastic changes is called metamorphosis. In animals that undergo metamorphosis, the young ones look very different from the adults. Examples: frog, silkworm, butterfly

9. Differentiate between internal fertilization and external fertilization.

Internal fertilization	External fertilization
Fertilization which takes place inside the female body is called internal fertilization. Internal fertilization occurs in higher order animals like dogs, cows, cats and humans.	Fertilization in which the fusion of male and female gamete takes place outside the female body is called external fertilization. External fertilization occurs in aquatic animals like fish and frogs.