Reaching the Age of Adolescence - Exemplar Solutions 1

CBSE Class 8 Science
NCERT Exemplar Solutions
CHAPTER 10
Reaching the age of Adolescence

MULTIPLE CHOICE QUESTIONS

1. The belief that the mother is completely responsible for the sex of the child is wrong because the child:

(a) gets sex chromosome only from the mother.

(b) develops in the body of the mother.

(d) gets sex chromosome only from the father.

Ans: (c) gets one sex chromosome from the mother and the other from the father.

Explanation: The sex of the unborn child depends upon whether the zygote has XX or XY chromosomes. A female has two X sex-chromosomes while a male has one X and one Y sex-chromosome. Each gamete has only one chromosome. An unfertilized egg always has one X chromosome. The egg is fertilized by a sperm which may contain either an X chromosome or a Y chromosome.

When a sperm containing an X chromosome fertilizes the egg, the zygote would possess two X chromosomes and would develop into a female child. On the other hand, when a sperm containing a Y chromosome fertilizes the egg, the zygote would possess one X and one Y chromosomes and would develop into a male child.

2. AIDS can spread from an infected person to another person through:

(a) sharing food

(b) blood transfusion

(d) a mosquito bite

Ans: (b) blood transfusion

Explanation: AIDS (Acquired Immuno Deficiency Syndrome) can get transferred from an infected person to a healthy person through blood transfusion. Therefore, it is recommended to use new syringe while taking an injection.

3. Given below are events that lead to pregnancy and development of embryo.

(i) Fertilization of egg

(ii) Maturation of egg

(iii) Release of egg

(iv) Embedding of embryo in thickened uterine wall.

Which of the following options gives the correct order of sequence in which they occur?

(a) i, ii, iii, iv

(b) ii, i, iii, iv

(d) ii, iii, i, iv

Ans: (d) ii, iii, i, iv

Explanation: With the onset of puberty in females, the eggs start to mature. They are released by the ovary. When the egg fuses with the sperm, it undergoes fertilization. The fertilization results in the formation of zygote.

The zygote then divides repeatedly giving rise to wall of cells that develops into an embryo and finally gets embedded in the thickened uterine wall for further development.

4. For the metamorphosis of tadpoles, which of the following elements must be available in water?

(a) chlorine

(b) carbon

(d) iodine

Ans: (d) iodine

Explanation: In frogs, metamorphosis is controlled by the hormone thyroxine. Thyroxine is produced by thyroid gland. The production of thyroxine requires the presence of iodine in water. Therefore, for the metamorphosis of tadpoles, it is necessary that iodine element must be available in water.

5. The most conspicuous visible change that occurs in boys during puberty is:

(a) development in voice box.

(b) increase in height.

(d) increased sweating.

Ans: (b) increase in height.

Explanation: The most conspicuous change at the age of puberty is the sudden increase in height. This is brought about by elongation of the bones of the arms and the legs. The arms and legs often grow faster than other body parts. Hormones control how the height increases.

6. Structures present in a cell which is responsible for determination of the sex of a baby is:

(a) cytoplasm

(b) cell membrane

(d) chromosome

Ans: (d) chromosome

Explanation: The nucleus of a cell contains thread-like structures celled chromosomes. Whether a baby will be a boy or a girl is determined by the chromosomes present inside the nucleus of the fertilised egg.