NCERT Book Class 8 Science Reaching The Age Of Adolescence

REACHIING THE AGE OF ADOLESCENCE

In the previous chapter, you have learnt how animals reproduce. It is only after ‘growing up’ to a certain age that human beings and many other animals can reproduce. Why can humans reproduce only after a certain age? In this chapter, you will learn about changes that take place in the human body after which a person becomes capable of reproduction. In Chapter 9, you have learnt about human reproductive organs. Here, we shall discuss the role that hormones play in bringing about changes that make a child grow into an adult.10.1 Adolescence and Puberty Boojho was celebrating his 12th birthday. After his friends left, Boojho and Paheli began chatting with their parents. Paheli studies in an all-girls school. She started laughing. She remarked that many of Boojho’s school friends, whom she met after a year, had suddenly shot up in height. Some of them were looking very funny with a hairy line above their lips. Her mother explained that the boys had grown up. Growth begins from the day one is born. But upon crossing the age of 10 or 11, there is a sudden spurt in growth which becomes noticeable. The changes taking place in the body are part of growing up. They indicate that you are Growing up is a natural process. The period of life, when the body undergoes changes, leading to reproductive maturity, is called adolescence.

Adolescence begins around the age of 11 and lasts upto 18 or 19 years of age. Since this period covers the ‘teens’ (13 to 18 or 19 years of age), adolescents are also called ‘teenagers’. In girls, adolescence may begin a year or two earlier than in boys. Also, the period of adolescence varies from person to person. The human body undergoes several changes during adolescence. These changes mark the onset of puberty. The most important change which marks puberty is that boys and girls become capable of reproduction. Puberty ends when an adolescent reaches reproductive maturity.

10.2 Changes at Puberty Increase in Height

The most conspicuous change during puberty is the sudden increase in height. At this time the long bones, that is, the bones of the arms and the legs elongate and make a person tall. There is no need for Paheli to worry. All parts of the body do not grow at the same rate. Sometimes the arms and legs or hands and feet of adolescents look oversized and out of proportion with the body. But soon the other parts catch up and result in a proportionate body. You must have noticed that height of an individual is more or less similar to that of some family member. This is because height depends on the genes inherited from parents. It is, however, very important to eat the right kind of food during these growing years. This helps the bones, muscles and other parts of the body get adequate nourishment for growth. You will find nutritional needs of adolescentsdiscussed later in the lesson.

Change in Body Shape Have you noticed that boys in your class have broader shoulders and wider chests than boys in junior classes? This is because they have entered the age o puberty when shoulders generally broaden as a result of growth. In girls, the region below the waist becomes wider In boys, the muscles of the body grow more prominently than in the girls. Thus, changes occurring in adolescent boys and girls are different. Development of Sex Organs Look up Fig. 9.1 and 9.3 of the previous lesson which shows sex organs of humans. 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. Also ovaries start releasing mature eggs. Reaching Mental, Intellectual and Emotional Maturity Adolescence is also a period of change in a person’s way of thinking.

Adolescents are more independent than before and are also self conscious. Intellectual development takes place and they tend to spend considerable time thinking. In fact, it is often the time in one’s life when the brain has the greatest capacity for learning  Sometimes, however, an adolescent may feel insecure while trying to adjust to the changes in the body and mind. But as adolescent learners, you should know that there is no reason to feel insecure. These changes are a natural part of growing up.

10.3 Secondary Sexual Characters

You have learnt in Chapter 9, that testes and ovaries are the reproductive organs. They produce the gametes, that is, sperms and ova. In girls, breasts begin to develop at pubertyand 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. Boy 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.

Exercises

1. What is the term used for secretions of endocrine glands responsible for changes taking place in the body?

2. Define adolescence.

3. What is menstruation? Explain.

4. List changes in the body that take place at puberty.

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

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

7. Choose the correct option.

(a) Adolescents should be careful about what they eat, because

(i) proper diet develops their brains.

(ii) proper diet is needed for the rapid growth taking place in their body.

(iii) adolescents feel hungry all the time.

(iv) taste buds are well developed in teenagers.

(b) Reproductive age in women starts when their

(i) menstruation starts.

(ii) breasts start developing.

(iii) body weight increases.

(iv) height increases.

(c) The right meal for adolescents consists of

(i) chips, noodles, coke.

(ii) chapati, dal, vegetables.

(iii) rice, noodles and burger.

(iv) vegetable cutlets, chips and lemon drink.

8. Write notes on—

(a) Adam’s apple.

(b) Secondary sexual characters.

(c) Sex determination in the unborn baby.

9. Word game : Use the clues to work out the words.

Across

3. Protruding voice box in boys

4. Glands without ducts

7. Endocrine gland attached to brain

8. Secretion of endocrine glands

9. Pancreatic hormone

10. Female hormone

Down

1. Male hormone

2. Secretes thyroxine

3. Another term for teenage

5. Hormone reaches here through blood stream

6. Voice box

Please refer to attached file for NCERT Class 8 Science Reaching The Age Of Adolescence