NCERT Book Class 8 Science Reproduction In Animals

REPRODUCTIION IIN ANIIMALS

Do you recall the processes of digestion, circulation and respiration which you have studied in your previous classes? These processes are essential for the survival of every individual. You have also learnt about the process of reproduction in plants. Reproduction is essential for the continuation of a species. Imagine what would have happened if organisms had not reproduced. You will realise that reproduction is very important as it ensures the continuation of similar kinds of individuals, generation after generation. You have already learnt in your previous class about reproduction in  plants. In this chapter, we shall learnhow reproduction takes place in animals.

9.1 Modes of Reproduction

Have you seen the young ones of different animals? Try to name some of the young ones by completing Table 9.1 as shown in examples at S. No. 1 and 5. You must have also seen the youn ones of various animals being born. Can you tell how chicks and caterpillars are born? How are kittens and puppies born? Do you think that these young ones looked the same before they were born as they do now? Let us find out. Just as in plants, there are two modes by which animals reproduce. These are: (i) Sexual reproduction, and (ii) Asexual reproduction.

9.2 Sexual Reproduction

Try to recall reproduction in plants which you studied in Class VII. You will remember that plants that reproduce sexually have male and female reproductive parts. Can you name these parts? In animals also, males and females have different reproductive parts or organs. Like plants, the reproductive parts in animals also produce gametesthat 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 and female gametes is called sexual reproduction. Let us find out the reproductive parts Male Reproductive Organs The male reproductive organs include a pair of testes (singular, testis), two sperm ducts and a penis (Fig. 9.1). The testes produce the male gametes called sperms. Millions of sperms are produced by the testes. Look at Fig. 9.2 which shows the picture of a sperm. Though sperms are very small in size, each has a head, a middle piece and a tail. Does it appear to be a single cell? Indeed, each female gametes called ova (eggs) (Fig. 9.4). In human beings, a single matured egg is released into the oviduct by one of the ovaries every month. Uterus is the part where development of the baby takes place. Like the sperm, an egg is also a single cell.

Fertilization

The first step in the process of reproduction is the fusion of a sper  and an ovum. When sperms come in contact with an egg, one of the sperms may fuse with the egg. Such fusion of the egg and the sperm is called fertilization (Fig. 9.5). 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 (Fig. 9.6). Did you know that the zygote is the beginning of a new individual? The process of fertilization is 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. Look at your brother or sister. See if you can recognise some characters in them similar to those of your mother or your father. Fertilization which takes place inside the female body is called internal fertilization. Internal fertilization occurs in many animals including humans, cows, dogs and hens.

Exercises

1. Explain the importance of reproduction in organisms.

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

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.

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

(i) fertilization. (ii) metamorphosis. (iii) embedding. (iv) budding.

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

(i) none. (ii) one. (iii) two. (iv) four.

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. ( )

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

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

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

8. What is metamorphosis? Give examples.

9. Differentiate between internal fertilization and external fertilization.

Please refer to attached file for NCERT Class 8 Science Reproduction In Animals