NCERT Solutions for Class 8 Science Chapter 9 Reproduction In Animals

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Updated at 2021-03-23


NCERT solutions for class 8 Science Chapter 9 Reproduction In Animals Exercise

Q.1 Explain the importance of reproduction in organisms.



NCERT Solutions for Class 8 Science Chapter 9 Reproduction In Animals


Answer :

Reproduction is essential for existence of life on earth.

Reproduction helps in maintaining the stability in the ecosystem.

Reproduction is necessary to ensure the continuation of a particular species on the earth.

Reproduction helps in the evolution of new species on earth.

Reproduction maintains a balance between the birth rate and death rate of the population.

Q.2 Describe the process of fertilisation in human beings.



NCERT Solutions for Class 8 Science Chapter 9 Reproduction In Animals


Answer :

Fertilization is defined as the process in which there is fusion of male gamete and female gamete.

The male gamete is the sperm that is released from the testis. Sperms are released in millions of number as it has to travel outside the male body. Thus, to increase the chances of its fusion with egg, it is released in more number. It is released along with semen which is a fluid that helps in the movement of sperms.

The female gamete is the ovum that is released from the ovary. Ovum is released once in a month as it is present inside the female body. It releases from the ovary into the fallopian tube where it stays till the sperm gets fertilized, otherwise it comes out of the body during menstruation.

During fertilization, one of the sperms fuses with the ova/egg. The nuclei of the sperm and the nuclei of the egg fuse to form a single nucleus resulting in the formation of a fertilized egg called as zygote. Zygote is a single cell having two nuclei, one from each gamete.

In human beings, the fertilisation takes place inside the female body, which is known as internal fertilisation.

Q.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



NCERT Solutions for Class 8 Science Chapter 9 Reproduction In Animals


Answer :

a) Internal fertilisation occurs
(i) in female body.

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

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

EXPLANATION

a) Internal fertilization is the fusion of an egg/ova and sperm cell during sexual reproduction inside the female body.

b) Metamorphosis is a biological process which involves sudden and abrupt changes in the body structure of the animal by growth using cell division and differentiation.

c) Though zygote is a single cell, but it has two nuclei as it contain one nuclei from the sperm and one nuclei from the egg/ova.

Q.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. ( )



NCERT Solutions for Class 8 Science Chapter 9 Reproduction In Animals


Answer :

a) Oviparous animals give birth to young ones. ( F )
b) Each sperm is a single cell. ( T )
c) External fertilisation takes place in frog. ( T )
d) A new human individual develops from a cell called gamete. ( F )
e) Egg laid after fertilisation is made up of a single cell. ( T )
f) Amoeba reproduces by budding. ( F )
g) Fertilisation is necessary even in asexual reproduction. ( F )
h) Binary fission is a method of asexual reproduction. ( T )
i) A zygote is formed as a result of fertilisation. ( T )
j) An embryo is made up of a single cell. ( F )

EXPLANATION

1) Oviparous animals are animals that lay their eggs, with little or no other embryonic development within the mother and the young ones are hatched by means of eggs.

2) Sperm is the male reproductive cell or gamete which takes part in sexual reproduction, in the formation of zygote.

3) External fertilization is a mode of reproduction in which a male organism's sperm fertilizes the female organism's ova/egg that is present outside the female body.

4) A new human individual develops from a cell called as zygote which is formed as a result of fusion of sperm and ova/egg.

5) Egg laid after fertilisation is made up of a single cell and this single cell is called as zygote. Zygote is a single cell that divides and forms embryo. With time, embryo divides and differentiates into different body parts, thus forming foetus.

6) Amoeba reproduces by binary fission. It is a type of asexual reproduction in which a single cell(parent cell) divides into two halves(daughter cells) along with their genetic material.

7) Fertilisation is not necessary in asexual reproduction because asexual reproduction occurs with the help of a single parent, which either divides to produce offspring or it grows its offspring on its body and later separates the offspring from its body.

8) Binary fission is a method of asexual reproduction. It is a type of asexual reproduction in which a single cell(parent cell) divides into two halves(daughter cells) along with their genetic material.

9) A zygote is formed as a result of fertilisation. Zygote is a single cell that divides and forms embryo. With time, embryo divides and differentiates into different body parts, thus forming foetus.

10) An embryo is a result of continuous division of zygote. Hence embryo is made up of many cells.

Q.5 Give two differences between a zygote and a foetus.



NCERT Solutions for Class 8 Science Chapter 9 Reproduction In Animals


Answer :

Zygote

(i) It is the first stage of development that takes place in a new organism.

(ii) It is formed when there is fusion of male gamete(sperm) and female gamete(ova/egg) by the process of fertilisation.

Foetus

(i) It is the last stage of development that further leads to the formation of the new organism.

(ii) It is formed when there is repeated division of the zygote into an embryo, which gets implanted in the uterus, thus deriving nutrition from the mother's body and this leads to the formation of the foetus.

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



NCERT Solutions for Class 8 Science Chapter 9 Reproduction In Animals


Answer :

Asexual reproduction is a mode of reproduction that does not involve the fusion of the male and the female gamete. It requires only one parent which undergoes a type of fission to generate exact copies of themselves with their genetic material. The offsprings that are produced as exact copies of their parents is called as clones.

(i) Binary fission

It is a type of asexual reproduction in which a single cell(parent cell) divides into two halves(daughter cells) along with their genetic material. Organisms that reproduce through binary fission are bacteria and amoeba. In amoeba, the division of cells can take place in any plane that involves the division of its nucleus into two nuclei, which is followed by the division of its body into two halves. Each half of the body receives a nucleus containing the genetic material and thus forming one daughter cell. A total of two daughter cells are produced in a binary fission from one parent cell.



(ii) Budding

In budding, the organism develops a bulge like projection on its body called as bud which further develops into an adult organism and separates itself from the parent body to lead an independent life. Thus a new organism is developed from a small part of the parent's body. This type of reproduction is shown by hydra.

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



NCERT Solutions for Class 8 Science Chapter 9 Reproduction In Animals


Answer :

Uterus is the female reproductive organ in which the embryo get embedded after fertilisation.

EXPLANATION

The uterus is a hollow muscular organ located in the female pelvis between the bladder and rectum. Functions of the uterus include nurturing the embryo into the foetus and then holding the baby till it is mature enough for birth.

The embryo gets implanted into the uterus lining through placenta and the umbilical cord to derive nourishment from blood vessels and to transfer waste materials from the foetus to the mother's body for excretion.

Q.8 What is metamorphosis? Give examples.



NCERT Solutions for Class 8 Science Chapter 9 Reproduction In Animals


Answer :

Metamorphosis is a biological process by which an animal physically develops after birth that involves a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation.

It is a process of transforming a larva into an adult by which animals undergo extreme rapid physical changes after the birth.

Frogs and insects are some examples of organisms that shows metamorphosis.

Q.9 Differentiate between internal fertilisation and external fertilisation.



NCERT Solutions for Class 8 Science Chapter 9 Reproduction In Animals


Answer :

Internal Fertilisation

1) The fusion of male gamete(sperm) and female gamete(ova), inside the female body is called as internal fertilisation.

2) There is high chances of survival of the young ones as their development occurs inside the female body under protection.

3) Example : Cow, hen, human beings etc.

External Fertilisation

1) The fusion of male gamete and female gamete outside the female body is called as external fertilisation.

2) There is low chances of survival of the young ones as their development occurs outside the female body, thus becoming vulnerable to their predators.

3) Example : Fish, frog, starfish etc.

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

Across

1. The process of the fusion of the gametes.
6. The type of fertilisation in a hen.
7. The term used for bulges observed on the sides of the body of Hydra.
8. Eggs are produced here.

Down

2. Sperms are produced in these male reproductive organs
3. Another term for the fertilized egg.
4. These animals lay eggs.
5. A type of fission in Amoeba



NCERT Solutions for Class 8 Science Chapter 9 Reproduction In Animals


Answer :

Across

1) Fertilization
6) Internal
7) Buds
8) Ovary

Down

2) Testis
3) Zygote
4) Oviparous
5) Binary


EXPLANATION

Across

1) Fertilization is the process of fusion of gametes to form a new organism of the same species. When the male gamete (i.e., the sperm) and the female gamete (i.e., the ovum) fuses with each other resulting the formation of a zygote, this process is called as fertilization. The new organism is formed when the zygote divides and forms embryo and this embryo further divides, thus resulting in the formation of the new organism.

6) Internal fertilization is the fusion of an egg/ovum and sperm inside the female body. The type of fertilization that is seen in hen is a type of internal fertilization.

7) Budding is a type of asexual reproduction in which a new organism develops from an outgrowth or bud due to cell division at a particular site. The small bulb-like projection coming out from the organism's body is called a bud.

8) The ovary is an organ found in the female reproductive system that produces an ovum. When an ovum is released, it travels down the fallopian tube, where it fertilized by a sperm and then the zygote enters into the uterus for further growth into a new organism. Ovary secretes estrogen and progesterone for the development of female reproductive organs and for the development of embryo during pregnancy.

Down

2) The testis is an organ found in the male reproductive system that produces an sperm. Testis is contained in a sac of skin called as scrotum. Testis secretes testosterone for the development of male reproductive organs.

3) A zygote is an eukaryotic cell formed by the fertilization of two gametes. The zygote begins as a single cell but divides rapidly in the following days after fertilization. The zygote's single cell contains 46 chromosomes. It gets 23 chromosomes from the sperm and 23 chromosomes from the ovum.

4) An oviparous animal is one that produces eggs, and the young ones are hatched after being expelled from the body. Many amphibians, birds, fish and reptiles are oviparous and often make nests to protect their eggs.

5) In the process of binary fission, an organism duplicates its genetic material and then divides into two parts (cytokinesis), with each new organism receiving one copy of DNA.



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