NCERT Solutions class 8 Science 9. Reproduction in animals Text Book Exercise

Exercise                                  

1. Explain the importance of reproduction in organisms.

Answer : The producuction of new individuals from their parrents is known as reproducation. Reproduction is very important as reproduction is very important as it ensures the continuation of similar kinds of individuals, generation after generation. if reproduction process does not exist,the generation of living beings will be vanished from the earth.              

2. Describe the the process of fertilization in human beings.

Answer : In human beings, sexual reproduction occurs in which reproduction results from the fusion of male and female gametes. the male reproductive organs are a pair of testes, sperm ducts and penis. The testes produce the male gametes called sperm Millions of sperm are produced by the testes. Through the sperms are very small in size, each has a head, a middle piece and a tail. Each sperm is a single cell with all the usual cell compomnents.The female reproductive oragans are a pair ofovaries, oviducts and the uterus. Ovary produces female gametes called ova (eggs). In human beings, single matured egg is released into the oviduct by one the ovaries every month. Uterus is the part where development of the baby takes place. Like sperm, egg is also  a single cell. The first step in the process of reproduction is the fusion of a sperm and ovum. Millions of sperm from the male are transferred into the female body. The sperm swim in the oviduct with the help of their tails to reach the egg. When they come in contact with the egg, one of the sperms may fuse with the egg. Such bfusion of the egg and the sperm is called fertilization. During fertilization, the nucleus of the sperm and the egg fuse to from a single nucleus. This results in the formation of a fertilized egg or zyote. The new individual inherits some charactristics from the mothe and some charecteristics from the father.

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 : (i) in female body.

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

(i) fertilization.

(ii) metamorphosis.

(iii) embedding.

(iv) budding.

Answer : (ii) metamorphosis.

(c) The number of nuclei present in a zygote is

(i) none.

(ii) one.

(iii) two.

(iv) four.

Answer : (ii) one.

4. Indicate whether the following statements are True (T) or False (F):

(a) Oviparous animals give birth to young ones. ( )

(b) Each sperm is a single cell. ( )

(c) External fertilization takes place in frog. ( )

(d) A new human individual develops from a cell called gamete. ( )

(e) Egg laid after fertilization is made up of a single cell. ( )

(f) Amoeba reproduces by budding. ( )

(g) Fertilization is necessary even in asexual reproduction. ( )

(h) Binary fission is a method of asexual reproduction. ( )

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

(j) An embryo is made up of a single cell. ( )

Answer : (a) (F), (b) (T), (c) (T), (d) (T), (e) (T), (f) (F), (g) (T), (h) (T), (i) (T), (j) (F).

5. Give two difference between a zygote and a foetus.

Answer : When fertilization takes place, the nuclei of the sperm and the egg fuse to form a single nucleus, which results in the formation of a fertilized egg or zyote. Zygote now begins to develop into an embryo. The embryo continues to develop in the uterus and produces body parts such as hands, legs, head, eyes, ears, etc. The stage of the embryo in which all the body parts are indentified ids called foeuts.

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

Answer : The type of reproduction in which on;y a single parent is involved is called asexual reproducation. Asexual reproducation takes  place in very small animals like Hydra and microscopic organisms like amoba.

Asexual reproduction in Hydra : 

Many bulges are found in the parent body of hydra. These bulges called buds, develops into new individuals.    

Make Fig.9.1. Buddings in Hydra

New individuals develop as outgrowths from a single parent. This is why this process is called budding.

Asexual reproducation in Amoeba : 

The pseudopodia, an irregular structure in the Amoeba, is for cathing food as well as for movement. It is single-called organism. The reproduction in Amobea begins by division of its nucleus into two nuclei.This is followed by division of its body into two with each part receiving a nucleus. Finally, two amoebae are produced from one Amoeba. This type of asexual reproduction in which animal reproduces by dividing into two individuals is called binary fission.

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

Answer : The embryo gets embedded in the wall of the uterus (of female) for further development. 

8. What is metamorphosis? Give examples.

Answer : The dra stic change which takes place during the development of an animal is callled metamorphosis. The animals that undergo metamorphosis are (i) silkworm (egg-larva or caterrpillar-pupa - adult), (ii) frog (egg-tadpole larva-adult), etc.

9. Differentiate between internal fertilization and external fertilization.

Anawer : The fertiliztion that takes places inside the femle body is called internal fertilization. This is observed in human beings and other animals such as hen, cows, dogs, etc.The fertilization that takes place outside the female body is called external fertilization. This is observed in frogs, fish, starfish, ets.