Reaching the Age of Adolescence

Q52. How does the height of boys and girls change during puberty?

Ans. At the time of puberty the long bones, that is, the bones of the arms and the legs elongate and make a person tall. Initially, girls grow faster than boys but by about 18 years of age, both reach their maximum height. The rate of growth in height varies in different individuals. Some may grow suddenly at puberty and then slow down, while others may grow gradually.

Q53. Prepare a Table having two columns depicting names of endocrine glands and hormones secreted by them.

Ans.

Q54. What is menstruation? Explain.

Ans. In females, the reproductive phase of life begins at puberty (10 to 12 years of age) and generally lasts till the age of approximately 45 to 50 years. The ova begin to mature with the onset of puberty. One ovum matures and is released by one of the ovaries once in about 28 to 30 days. During this period, the wall of the uterus becomes thick so as to receive the egg, in case it is fertilised and begins to develop. This results in pregnancy. If fertilisation does not occur, the released egg, and the thickened lining of the uterus along with its blood vessels are shed off. This causes bleeding in women which is called menstruation.

Q55. What are sex hormones? Why are they named so? State their function.

Ans. Sex hormones are chemical substances produced by a sex gland or other organ. For example, the testes make male sex hormone called testosterone and the ovaries make female sex hormone called estrogen. These hormones affect the sexual features of an organism. Hence they are called sex hormones.

Functions

Testosterone – It produces male secondary sexual characteristics in boys such as deeper voice, growth of moustache and beard, broad shoulders and chest, adam’s apple, more muscles, development of reproductive organs etc.

Estrogen – It produces female secondary sexual characteristics in girls such as development of breasts, broader hips, development of reproductive organs etc.

Q56. List changes in the body that take place at puberty.
Or
State some of the changes which take place in boys and girls during adolescence.

Ans. Changes at puberty

                          i.        Sudden increase in height and weight.

                         ii.        Boys develop broader shoulders and wider chests. In girls, the region below the waist becomes wider.

                        iii.        In boys, the muscles of the body grow more prominently than in the girls.

                        iv.        Boys develop larger voice boxes. The growing voice box in boys can be seen as a protruding part of the throat called Adam’s apple.

                         v.        Development of pimples and acne on the face due to the increased activity of sebaceous glands and sweat glands present in the skin.

                        vi.        At puberty, male sex organs like the testes and penis develop completely. The testes also begin to produce sperms. In girls, the ovaries enlarge and eggs begin to mature.

          vii.        In girls, breasts begin to develop at puberty and boys begin to grow facial hair, that is, moustaches and beard.

          viii.        Boys also develop hair on their chest. In both, boys and girls, hair grows under the arms and in the region above the thighs or the pubic region.

Q57. Write notes on—
(a) Adam’s apple.
(b) Secondary sexual characters.
(c) Sex determination in the unborn baby.

Ans. (a) Adam’s apple - At puberty, the voice box or the larynx begins to grow. Boys develop larger voice boxes. The growing voice box in boys can be seen as a protruding part of the throat called Adam’s apple.

(b) Secondary sexual characters - In girls, breasts begin to develop at puberty and boys begin to grow facial hair, that is, moustaches and beard. As these features help to distinguish the male from the female they are called secondary sexual characters. Boys also develop hair on their chest. In both, boys and girls, hair grows under the arms and in the region above the thighs or the pubic region.

(c) Sex determination in the unborn baby - All human beings have 23 pairs of chromosomes in the nuclei of their cells. Two chromosomes out of these are the sex chromosomes, named X and Y. A female has two X chromosomes, while a male has one X and one Y chromosome. The gametes (egg and sperm) have only one set of chromosomes. The unfertilised egg always has one X chromosome. But sperms are of two kinds. One kind has an X chromosome, and the other kind has a Y chromosome. When a sperm containing X chromosome fertilises the egg, the zygote would have two X chromosomes and develop into a female child. If the sperm contributes a Y chromosome to the egg (ovum) at fertilisation, the zygote would develop into a male child.

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