NCERT Class 8 Science Chapter 10 - Reaching the Age of Adolescence

Chapter 10 - Reaching the Age of Adolescence

Question 1: What is the term used for secretions of endocrine glands responsible for changes taking place in the body?
Answer:
The term used for secretions of endocrine glands responsible for changes taking place in the body is hormones. Hormones are chemical substances which are produced by endocrine glands.

Question 2: Define adolescence.
Answer:
Adolescence is a period of life, when body undergoes changes leading to reproductive maturity. The period of adolescence is normally from 11 years to 19 years. Adolescents are also called ‘teenagers’. The body at this stage undergoes important changes and these mark the period of puberty.

Question 3: What is menstruation? Explain.
Answer:
In female the ovary produces one egg every month and the uterus prepares to receive the fertilized egg. Its wall become thick with blood vessels. If fertilization doesn’t takes place then the uterus wall breaks and comes out vagina as blood and mucous. This cycle takes place every month and is called menstruation cycle. The beginning of menstrual cycle is called menarch. When the menstrual cycle stops at 40-50 years, it is called menopause.

Question 4: List the changes in the body that take place at puberty.
Answer:
The changes in the body that take place at puberty are
• Increase in height
• Change in body shape
• Voice change
• Increased activity of sweat and sebaceous glands
• Development of sex organs
• Reaching mental, intellectual and emotional maturity

Question 5: Prepare a table having 2 columns depicting name of endocrine glands and hormones.
Answer:

Question 5 Answer

Question 6: What are sex hormones? Why are they named so? State their function.
Answer:
The hormones which help and control the formation of secondary sexual characters are called sex hormones. They are named so because they control the sexual activities and are secreted by males and females separately.
• Male sex hormones - It is also called testosterone. It is secreted by testes and causes changes in secondary sexual characters of boys like growth of facial hair etc.
• Female sex hormones - It is also called estrogen. It is secreted by ovaries and causes changes in secondary sexual characters of girls like appearance of mammary glands etc.

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

b) Reproductive age in women starts when their
i) menstruation starts.
ii) breasts start developing.
iii) body weight increases.
iv) height increases.
Answer:
i) menstruation starts.

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.
Answer:
ii) chapati, dal, vegetables.

Question 8: Write notes on -
a) Adam’s apple
b) Secondary sexual characters
c) Sex determination in the unborn baby
Answer:

a) The protruding part of the throat is called Adam's apple. It is the enlarged voice box or larynx which gets enlarged and visible from outside in boys at the onset of puberty. This makes the voice of boys hoarse.

b) At puberty some changes occur in both males and females that distinguish them from each other. The features that develop them are called secondary sexual characters.

c) Human beings have 23 pairs of chromosomes in the nucleus of the cell. Out of this two chromosomes are sex chromosomes (X and Y). The females have two X chromosomes and the males have X and Y chromosome. The sperms and eggs have one set of sex chromosomes. Some sperms have X chromosome and some have Y chromosome. All eggs have X chromosomes. If a sperm having X chromosome fuses with an egg having X chromosome, the child will be a girl. If a sperm having Y chromosome fuses with an egg having X chromosome, the child will be a boy.

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

Question 9

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
7. Term for changes at adolescence
Answer:

Question 9 Answer

Question 10: The table below shows the data on likely heights of boys and girls as they grow in age. Draw graphs showing height and age for both boys and girls on the same graph paper. What conclusions can be drawn from these graphs?

Question 10

Answer:

Question 10 Answer

We conclude that initially boys grow faster than girls from 0-8 years, and girls grow faster than boys from 8-16 years. But both reach their maximum height at the age of 20. Here boys show a greater increase in height than girls.

Question 11: Define
a) Adolescence
b) Puberty
c) Adam’s apple
d) Hormones
e) Endocrine glands
f) Estrogen
g) Testosterone
h) Adrenalin
i) Target site
j) Thyroxine
Answer:

a) Adolescence is a period of life, when body undergoes changes leading to reproductive maturity. The period of adolescence is normally from 11 years to 19 years. Adolescents are also called ‘teenagers’. The body at this stage undergoes important changes and these mark the period of puberty.

b) It is a period, during which, the human body undergoes changes in their body which leads to sexual maturity. The most important change, which marks puberty is that boys and girls become capable of reproduction.

c) The protruding part of the throat is called Adam's apple. It is the enlarged voice box or larynx which gets enlarged and visible from outside in boys at the onset of puberty. This makes the voice of boys hoarse.

d) Hormones are chemical substances which are synthesized at one place and travels through the blood stream and act upon target site.

e) A gland which doesn’t have duct or tube and secretes its product directly into bloodstream is called endocrine gland. They make chemical substance called hormones.

f) The female hormone which controls secondary sexual characters in female is called estrogen.

g) The male hormone which controls secondary sexual characters in male is called testosterone.

h) It is produced by adrenal gland. It helps the body to adjust stress when we are angry or worried.

i) Endocrine glands release hormones into the bloodstream to reach a particular body part are called target site.

j) It is produced by thyroid. Its defiency causes goitre (swelling of throat).


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