Reproduction in Animals - Exemplar Solutions 4

CBSE Class 8 Science
NCERT Exemplar Solutions
Reproduction in Animals

24. How can we say that fish exhibits external fertilisation?
Ans. Female fishes release eggs into water and male fish releases sperms. Sperms swim randomly in water and comes in contact with the eggs. The nucleus of the sperm moves into the egg and fuses with it. Since fertilisation occurs in water, outside the female body, it is external fertilisation.

After observing Fig. 9.3 answer the following.
a. Read the following statements and label them in the figure:
(i) The part which produces female gametes.
(ii) The part where development of the baby takes place.
(iii) The part through which the developing embryo passes to reach the uterus.
b. Explain the future development of the embryo that would take place after it gets embedded in the uterus.

26. Hens and frogs are both oviparous exhibiting different types of fertilisation. Explain.
Ans. Hen is  an oviparous animal with  internal fertilisation. The fertilised egg develops into an embryo inside the body. However, the development of chick from the embryo takes place outside the body.
Frogs are oviparous in which both fertilisation and development of  embryo and young ones occur outside the body.

27. Observe the following figures.
(i) Identify the stages a to d in Fig. 9.4 during development of human baby.
(ii) Arrange the stages in correct sequence of development.
(iii) Explain the development that takes place in any one stage.
Ans. (i) (a) Embedding of the embryo in the uterus.
(b) Fertilisation.
(c) Zygote formation and development of an embryo from the zygote.
(d) Zygote showing fusion of nuclei.
(ii) The correct sequence is c, b, d, a
(iii) Zygote formation
The sperm and the egg nuclei fuses to form a single nucleus resulting in the formation of a fertilised egg or zygote.