NCERT Solution For Class 8 Science, Chapter 9 – Reproduction in Animals

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NCERT Solution For Class 8 Science, Chapter 9 – Reproduction in Animals provides us with all-inclusive information on all concepts. As students would have to learn the basics about the subject in class 8, this curriculum for class 8 is comprehensive study material, which explains the concepts in a great way.

1. Explain the importance of reproduction in organisms.

Sol:

The importance of reproduction in organisms is as follows• Reproduction is called a biological process in which organisms give rise to their closed springs.• It helps in maintaining the continuity of a particular breed and helps in increasing the population of the species.• Reproduction is for the survival of all living things.

2. Describe the process of fertilisation in human beings.

Sol:

·Fertilization is defined as the process in which the fusion of the male gametes and the female gametes occurs.·        Male gametes or sperm are released from the male reproductive organ called the penis.·        Sperm released through the vagina to enter the female body.·        From the vagina, sperm travel through the fallopian tube where they meet the egg.·        From there, the process of fertilization takes place in the fallopian tube.·        Male gametes cell (sperm) and female gametes cell (egg) combine to form zygotes.·        The zygote rapidly divides to form a group of cells called morula, which become embryos after about five days. The embryo remains present for about eight weeks after fertilization.

3. Choose the most appropriate answer.

(a) Internal fertilisation 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) fertilisation

(ii) metamorphosis

(iii) embedding

(iv) budding

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

(i) none

(ii) one

(iii) two

(iv) four

Sol:

1. a) (i) in female body.
2. b) (ii) metamorphosis
3. c) (iii) two
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 fertilisation takes place in frog. ( )

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

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

(f) Amoeba reproduces by budding. ( )

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

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

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

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

Sol:

1. a) False
2. b) True
3. c) True
4. d) False
5. e) True
6. f) False
7. g) False
8. h) True
9. i) True
10. j) False
11. Give two differences between a zygote and a foetus.

Sol:

Zygote:

• It is the earliest stage of development
• It is formed by the fusion of male and female gametes
• It is a single cell
• The zygote divides several times to form an embryo
• The zygote normally lasts a week and then develop into its next stage.

Foetus

• It is the last developmental stage of an organism
• The stage of the embryo that shows all the main recognizable body parts of a mature organism.
• The foetus stage occurs after the embryo stage.
• Foetus mainly undergoes internal development.

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

Sol:

In this type of reproduction, the offspring arises from a single organism without the fusion of male and female gametes. It never changes the number of chromosomes.

Binary fission in amoeba

• It is a type of asexual reproduction in which a cell divides into two parts.• It is a unicellular organism which consists of cell membrane, cell wall and cytoplasm.• Cell division can occur on any plane.• In this process, the nucleus of the amoeba first acts to form two daughter nuclei known as chirokinesis.• Finally, the body is divided into two parts of the nucleus respectively.

Budding in hydra

· Organisms such as Hydra use regenerative cells for reproduction in the process of reproduction.·        The first step is the formation of buds, and it develops as a small protrusion on the parent’s body.·        As an extension of the bud, it acquires the characteristics of the original organism.·        Once developed, it can be separated from the parent body and developed into a new person.·        In some rare cases, buds interconnected cannot be separated.·        There are also methods such as fragmentation, multiple fragmentation etc.

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

Sol:

• In the female reproductive organ, the embryo gets attached to the uterus.
• Once it gets attached, there occurs the formation of body parts like legs, hands, eyes etc.
• The embryo is then called a foetus.

8. What is metamorphosis? Give examples.

Sol:

• It is defined as a process in which the body composition of an animal changes abruptly through cell growth and differentiation.• It is a biological process.• Such examples are frogs and insects. Life cycle of a frog:The tadpoles that emerge from the eggs will have gills, tails, etc.They can swim easily in water.It undergoes a sudden change and develops into a mature frog.

9. Differentiate between internal fertilisation and external fertilisation.

Soln:

Fertilization, in general, is defined as the fusion of a male and a female gametes.

Internal fertilization

It occurs inside the female body.

There is a high probability of survival of the offspring.

Internal fertilization protects fertilized eggs or embryos from harsh environments.

Examples are cows, humans, dogs, monkeys etc.

External fertilization

It occurs outside the female body.

Children are less likely to survive.Most aquatic animals use this type of fertilization and the advantage of external fertilization is that it produces a large number of offspring due to external threats.Examples are fish, frogs, creatures etc.

10. Complete the crossword puzzle using the hints given below.

Across

1. The process of the fusion of the gametes.
2. The type of fertilisation in hen.
3. The term used for bulges observed on the sides of the body of hydra.
4. Eggs are produced here.

Down

2. Sperms are produced in these male reproductive organs.
3. Another term for in vitro fertilisation.
4. These animals lay eggs.
5. A type of fission in amoeba

Sol:

Across

1) Fertilization

6) Internal

7) Buds

8) Ovary

Down

2) Testis

3) Zygote

4) Oviparous

5) Binary

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