# Class 8 Science NCERT Solutions for Chapter – 10 Reaching the Age of Adolescence

### Reaching the Age of Adolescence

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

The term used for secretions of endocrine glands is hormones, which are responsible for various changes taking place in the body.

Question 2.

The period of life when the body undergoes changes, leading to reproductive maturity, is called adolescence.

Question 3.
What is menstruation? Explain.

When the uterus receives the egg and it is fertilized, pregnancy occurs. If fertilization 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.

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

The onset of puberty brings about :

1. Growth of the reproductive organs which begin to function.
2. Hair grows at various places of the body. Breasts develop in girls and facial hair (mustache and beard) appear in boys.
3. The voice of the boys becomes hoarse as the voice box enlarges during adolescence.

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

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

Hormones secreted by testes and ovaries are termed as sex-hormones.

• They are named so because they are secreted by the reproductive organs.
• Functions of sex-hormones.
• These hormones are responsible for the secondary sexual characters of males and females.

Question 7.
Choose the correct option:

1. Proper diet develops their brains.
2. Proper diet is needed for the rapid growth taking place in their body.
3. Adolescents feel hungry all the time.
4. Taste buds are well developed in teenagers.

2. Proper diet is needed for the rapid growth taking place in their body.

(b) Reproductive age in women starts when their:
1. Menstruation starts.
2. Breasts start developing.
3. Body weight increases.
4. Height increases.

1. Menstruation starts.

(c) The right meal for adolescents consists of
1. Chips, noodles, coke.
2. Chapati, dal, vegetables.
3. Rice, noodles, and burger.
4. Vegetable cutlets, chips, and lemon drink.

2. Chapati, dal, vegetables.

Question 8.
Write notes on :

At puberty, the voice box or the larynx begins to grow. The growing voice box in boys can be seen as a protruding part of the throat called Adam’s apple. This makes a boy’s voice hoarse.

(2) Secondary sexual characters.

In girls, breasts begin to develop at puberty and boys begin to grow facial hair, that is, mustaches and beards. As these features help to distinguish the male from the female, they are called secondary sexual characters.

(3) 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 an X and one Y chromosome.

The unfertilized egg always has one X chromosome. But, testes produce two kinds of sperms. One kind has an X chromosome and the other kind has a Y chromosome.

When a sperm containing X chromosome fertilizes 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 fertilization, the zygote would develop into a male child. This is how sex determination in the unborn baby occurs.

Question 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 a 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 the bloodstream
6. Voicebox
7. Term for changes at adolescence.

Question 1.
Why can humans reproduce only after a certain age?

Humans reproduce only when they get reproductive maturity. 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 up to 18 or 19 years of age.

Question 2.
Paheli and Boojho realized that sudden increase in height and a hairy line above the lips in boys were signs of adolescence. They wanted to know about other changes at puberty.

The other changes on attaining adolescence are as follows :

(1) In boys: Voice changes. It becomes hoarse. Many boys get acne and pimples on the face. Sex organs like testes and penis develop completely and testes also begin to produce sperms.

(2) In girls: Region below the waist becomes wider, ovaries and breasts enlarge and eggs begin to mature. Ovary starts releasing matured eggs.

10.2 Changes at Puberty

Activity 10.2

Question 1.
Use the data given in Activity 10.1 to draw a graph. Take age on the x-axis and percent growth in height on the y-axis. Highlight the point representing your age on the graph. Find out the percentage of height you have already reached. Calculate the height you might eventually reach. Tally your graph with the one given here (Fig. 10.1).

Presently, my height is 120 cm and the point of my age, i.e., 14 years touches the 92% mark on the height axis.
So, my height

$=\frac{120 \mathrm{~cm}}{93} \times 100$
= 129 cm tall

10.5 Reproductive Phase of Life in Humans

Question 3.
Paheli says that the reproductive life of a woman lasts from menarche to menopause. Is she right?

Yes, she is absolutely right.

10.8 Role of Hormones in Completing the Life History of Insects and Frogs

Question 4.
If people do not have enough iodine in their diet, will they get goiter caused by lack of thyroxine?

Yes, if people do not have enough iodine in their diet, then they may suffer from goiter. To get rid of this disease, people should use iodized salt.

Activity 10.3

Question 1.
Collect information from magazines or from doctors and prepare a note on the importance of consuming iodized salt. You can also look for this information on the internet.

Iodine prevents it from getting goiter. This is due to the fact that the production of thyroxine requires iodine. Thyroxine is produced by the thyroid. The lack of iodine in the food can cause goiter, which results in retarded mental and physical growth.

10.9 Reproductive Health

Question 5.
Check items for lunch and dinner in your meal. Is the meal balanced and nutritious? Does it include cereals which give energy and milk, meat, nuts, and pulses which provide protein for growth? Also, does it include fats and sugar that give energy? What about fruits and vegetables which are protective foods?

I take bread (chapatis), rice, dal, vegetables, etc., for lunch and dinner as well. After lunch and dinner, I take fruits like apples, bananas, etc. Before going to bed the night, I drink a glass of milk.

I think my lunch and dinner are not only nutritious but also balanced. I don’t take chips, soft drinks, packed or tinned snacks, etc.

Activity 10.4

Question 1.
Make a group with your friends. Write down the items of food in your breakfast, lunch and. dinner you had on the previous day. Identify the items responsible for proper growth. Also identified the junk food that you consumed the previous day.

I have three friends, Ram Chatterjee, a Bengali; Preetam Singh, a Punjabi Sikh; and Kunju Ratnam, a south Indian. This is the group I am in. Given below are the items of food that we have in our breakfast, lunch, and dinner :

(1) Myself

Breakfast:

• Vegetable, and a glass of milk.

Lunch:

• Chapati
• Rice
• Vegetable
• Dal
• Curd
• An orange, or an apple.

Dinner:

• Chapati
• Dal
• Vegetable
• Kheer
• A fruit and a glass of milk.

There is a little change in the food items. Over and above, my meal is a balanced food and I think this will give me proper growth.

(2) Ram Chatterjee

Breakfast:

• Butter and tea.

Lunch:

• Rice
• Fish curry and vegetables (fried).

Dinner:

• Chapati
• Rice
• Dal
• Vegetable and curd.

Up to some extent, the diet is balanced. So, the proper growth of the body and mind is possible.

(3) Kunju Ratnam

Breakfast:

• Sambhar and tea.

Lunch:

• Rice
• Sambhar
• Curd

Dinner:

• Same as lunch + chapati.

This meal is also not a balanced one. So, proper growth may not be possible.

(4) Preetam Singh

Breakfast:

• Chhole-butter or puri-vegetable with tea.

Lunch:

• Chapati
• Dal
• Meat/fish etc. + curd

Dinner:

• Chapati
• fish/meat/egg curry + a glass of milk.

To some extent, this meal is a balanced one. Proper growth is possible.

Activity 10.6

Question 1.
Collect data on the number of children in your class who exercise regularly and who do not exercise regularly. Did you notice stay difference in their fitness and health? Prepare a report on the benefits of regular exercise.

Yes, I notice some differences in fitness and health of children who do exercise regularly and the children who do not exercise regularly. The children who do regular exercise are very healthy and fit, not only my body but also by the mind. And those who do not do exercise regularly often remain sick. They lack concentration while studying.

#### Class 8 Science NCERT Solutions for Chapter – 11 Force and Pressure

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