NCERT Exemplar Solutions: Reproduction in Animals | Science Class 8 PDF Download

Multiple Choice Questions

Q.1. Sets of reproductive terms are given below. Choose the set that has an incorrect combination.
(a) sperm, testis, sperm duct, penis
(b) menstruation, egg, oviduct, uterus
(c) sperm, oviduct, egg, uterus
(d) ovulation, egg, oviduct, uterus
Ans: c
Explanation:
Sperm is male gamete, the egg is female gamete, oviduct and uterus are part of the female reproductive system. Hence option c) is an incorrect combination.

Q.2. In humans, the development of the fertilised egg takes place in the
(a) ovary
(b) testis
(c) oviduct
(d) uterus
Ans: d
Explanation:
The development of the fertilised egg takes place in the uterus. Embryo gets embedded in the wall of the uterus for development by implantation.

Q.3. In the list of animals given below, the hen is the odd one out.

human being, cow, dog, hen

The reason for this is
(a) it undergoes internal fertilisation.
(b) it is oviparous.
(c) it is viviparous.
(d) it undergoes external fertilisation.
Ans: b
Explanation:
The hen is oviparous, it lays the egg and the young one gets hatched later. Rest of the animals provided are viviparous. They give birth to young ones after they are developed completely.

Q.4. Animals exhibiting external fertilisation produce a large number of gametes. Pick the appropriate reason from the following.
(a) The animals are small in size and want to produce more offsprings.
(b) Food is available is plenty of water.
(c) To ensure a better chance of fertilisation.
(d) Water promotes the production of a large number of gametes.
Ans: c
Explanation:
Because they release gametes in water chances of getting washed away by water, wind and rain are more. Hence To ensure better chance of fertilisation. A large number of gametes are produced by Animals exhibiting external fertilization.

Q.5. Reproduction by budding takes place in
(a) hydra
(c) paramecium
(b) amoeba
(d) bacteria
Ans: a
Explanation:
Paramecium, Amoeba and bacteria reproduce by binary fission. Hydra reproduces by budding where a bud detaches from the parent which grows into a complete organism.

Q.6. Which of the following statements about reproduction in humans is correct?
(a) Fertilisation takes place externally.
(b) Fertilisation takes place in the testes.
(c) During fertilisation, egg moves towards the sperm.
(d) Fertilisation takes place in the human female.
Ans: d
Explanation:
Male gametes are introduced into a female’s body through the vagina. Sperm reach uterus through the oviduct. At uterus, egg gets fertilized by sperm to form a zygote.

Q.7. In human beings, after fertilisation, the structure which gets embedded in the wall of uterus is
(a) ovum
(b) embryo
(c) foetus
(d) zygote
Ans: b
Explanation:
Egg fuses with sperm to form the zygote which will divide to form a clump of hundreds of cells which form the embryo. The process of moving down embryo from oviduct into the uterus is called as implantation.

Q.8. Aquatic animals in which fertilisation occurs in water are said to be:
(a) viviparous without fertilisation.
(b) oviparous with external fertilisation.
(c) viviparous with internal fertilisation.
(d) oviparous with internal fertilisation.
Ans: b
Explanation:
Aquatic animals lay eggs and release sperms into the water for fertilization to take place. Young one is formed outside the body hence it is called external fertilization.

Q.9. After fertilisation, the resulting cell which gives rise to a new individual is the
(a) embryo
(b) ovum
(c) foetus
(d) zygote
Ans: d
Explanation:
The zygote is the beginning of the formation of a new individual. All the multicellular organisms start their life from single-celled zygote.

Q.10. In human beings, the correct sequence of events during reproduction is
(a) gamete formation, fertilisation, zygote, embryo
(b) embryo, zygote, fertilisation, gamete formation
(c) fertilisation, gamete formation, embryo, the zygote
(d) gamete formation, fertilisation, embryo, the zygote
Ans: a
Explanation:
In humans, male gametes fuse with female gametes to fertilise in the female ovary. Fertilised sperm and egg form zygote which will divide repeatedly to form the embryo.

Very Short Answer Questions

Q.1. Although 2 cells called gametes fuse, the product formed is a single cell called the zygote. Justify.
Ans: During fertilization, only the nucleus of the sperm gets implanted into the uterus to form a zygote. Then sperm degenerates. Hence fused cell is called gamete.
Stages in the lifecycle of silkworm are given below. Write them in sequential order.

Q.2. Stages in the lifecycle of silkworm are given below. Write them in sequential order.
pupa, silkworm, egg, silkmoth
Ans:

a) Egg.

b) Pupa.

c) Silkmoth.

d) Silkworm.

Q.3. What is the importance of reproduction?
Ans: Reproduction ensures the continuation of species from generation to generation.

Q.4. In markets, eggs of birds are available but never eggs of dogs. Why?
Ans: Because the dog is viviparous. It does not lay an egg. It gives birth to a new one.

Q.5. The eggs of frogs do not have shells for protection, yet they are safe in the water. How?
Ans: Jelly like covering on the eggs give the protection Hence frog’s eggs are safe in the water.

Short Answer Questions

Q.1. Fill up the blanks with the terms given below:

boy, asexual, binary, single, nucleus

Amoeba is a ___________ celled organism. It reproduces by ___________ reproduction. The process of reproduction begins by the division of its ___________ into two. This is followed by the division of its ___________ into two. This type of reproduction is called ___________ fission.
Ans:
Amoeba is a single-celled organism. It reproduces by asexual reproduction. The process of reproduction begins with the division of its nucleus into two. This is followed by the division of its body into two. This type of reproduction is called binary fission.

Q.2. The term metamorphosis is not used while describing human development. Why?
Ans: Because body parts of humans will be present by birth. Whereas in metamorphosis parts of adults are different from the young ones.

Q.3. Mother gives birth to a baby but the baby has characters of both parents. How is this possible?
Ans: Though the mother gives birth to baby fertilization involves the fusion of gametes from both the parents. Hence character is obtained by both the parents.

Q.4. How is reproduction in hydra different from that in amoeba?
Ans: Hydra reproduces by budding where a bud detaches from the parent which grows into a complete organism. Whereas amoeba reproduces by binary fission. The process of reproduction begins with the division of its nucleus into two. This is followed by the division of its body into two.

Q.5. State whether the following statements are True or False. If false, correct the statement:
(a) External fertilisation can occur both in water and on land.
(b) The eggs of fish are covered by hard shells for protection.
(c) The human egg has a head, middle piece and tail.
(d) In adult human females, a single mature egg is released into an oviduct every month.
Ans:

1. False- External fertilisation can occur only in water.
2. False- eggs of fish are covered by jelly-like substance for protection.
3. False- Human sperm has a head, middle piece and tail.
4. True

Q.6. Why do only male gametes have a tail?
Ans: Because sperm need to be motile to reach the non-motile egg in the ovary of the female.

Q.7. What does Figure represent?

Ans: The figure shows Binary fission of amoeba with a dividing nucleus.

Q.8. Observe the figure given as Figure and answer the questions that follow.

(a) Label A and B.
(b) Identify the process.
(c) What happens during this process and what is formed?
Ans:
(a) A-sperm; B-ovum (egg)
(b) Fertilisation
(c) Sperm nucleus fuses with the egg nucleus to form the zygote.

Long Answer Questions

Q.1. How can we say that fish exhibits external fertilisation?
Ans: Female fish releases eggs into the water and male fish releases sperm into the water. Sperm swim randomly in water to reach the egg. The nucleus of the sperm reaches the egg and fuses to form the zygote. Since fertilization takes place externally. It is called external fertilization.

Q.2. After observing Figure answer the following.

a) Read the following statements and label them in the figure:

1. The part which produces female gametes.
2. The part where the development of the baby takes place.
3. The part through which the developing embryo passes to reach the uterus.

Ans: 

1. Ovary
2. Uterus
3. Oviduct

b) Explain the future development of the embryo that would take place after it gets embedded in the uterus.
Ans: Developing embryo gets embedded in the wall of the uterus for further development. The embryo continues to develop in the uterus. It gradually develops body parts such as hands, legs, head, eyes, ears etc. The stage of the embryo in which all the body parts can be identified is called a foetus (Figure). When the development of the foetus is complete, the mother gives birth to the baby.

Q.3. Hens and frogs are both oviparous exhibiting different types of fertilisation. Explain.
Ans: In Hens internal fertilisation takes place. The fertilised egg develops inside the female body but the development of chick from the embryo takes place outside the body.

On the other hand in frogs both fertilisation and development of zygote to an embryo and young ones occurs outside the body.

Q.4. Observe the following figures.
(a)

(b)

(c)

(d)

1. Identify the stages a to d in Figure during the development of the human baby.
2. Arrange the stages in the correct sequence of development.
3. Explain the development that takes place in any one stage.

Ans:

1. The stages during the development of the human baby:
   • Embedding of the embryo in the uterus.
   • Fertilisation.
   • Zygote formation and development of an embryo from the zygote.
   • Zygote showing fusion of nuclei.
2. The correct sequence of development is:
   • Zygote formation and development of an embryo from.
   • Fertilisation.
   • Zygote showing fusion of nuclei.
   • Embedding of the embryo in the uterus.
3. Zygote formation
   The sperm and the egg nuclei fuse to form a single nucleus resulting in the formation of a fertilised egg or zygote.