NCERT Solutions for Class 8 Science Chapter 10 Reaching The age of adolescence

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

Answer:

Hormones are chemical messengers produced by endocrine glands to control different body changes. The endocrine system's secretions have a key role in governing growth, development, and other body functions in humans.

Q2. Define adolescence

Answer:

• Adolescence is the period of life when the body changes in some ways, resulting in reproductive maturity.
• It generally starts at the age of 11 and continues until the age of 18 or 19 years. It comprises the teenage years (13 to 18 or 19 years), and those at this level are called teenagers.
• In females, adolescence can begin a year or two before that in males. However, the length of adolescence differs from individual to individual.

Q3. What is menstruation? Explain

Answer:

In women, the ova mature at puberty (about 10 to 12 years of age). One ovum matures every 28-30 days and is released from the ovaries. At the same time, the lining of the uterus gets thickened to accommodate a potential pregnancy. In case fertilization does not happen, the thickened uterine lining and blood vessels are shed from the body along with the unfertilized egg, leading to bleeding. Menstruation is referred to as such a process.

Q4. List changes in the body that take place at puberty.

Answer: Changes That Occur During Puberty:

• Increase in body height and weight.

• In males, the chest and shoulders widen, while in females, the region below the waist becomes broader.

• The voice box (larynx) enlarges in males, forming the Adam’s apple, while in females, it remains smaller.

• Males develop a deep voice, whereas females have a high-pitched voice.

• Secondary sexual characteristics develop, including underarm hair, facial hair (beard), and body hair in both genders.

• The male and female reproductive organs become fully functional.

• In males, the testes start producing sperm.

• In females, the ovaries enlarge, eggs mature, and menstruation begins.

Q5. Prepare a Table having two columns depicting names of endocrine glands and hormones secreted by them.

Answer:

Q6. What are sex hormones? Why are they named so? State their function.

Answer:

Sex hormones are chemical substances secreted by the male and female sex organs. For instance, testosterone is a male sex hormone secreted by the testes, while estrogen is the female sex hormone secreted by the ovaries.

They are secreted by the sex organs and affect the growth of sexual features, hence being referred to as sex hormones.

Functions of Sex Hormones:

Estrogen (Female Hormone): It is responsible for the formation of breasts (mammary glands), which secrete milk to newborns. It also helps in the growth and development of female reproductive organs.

Testosterone (Male Hormone): It is responsible for the development of secondary sexual features like beard, body hair, and male reproductive organ development.

Q7. Choose the correct option.

(a) Adolescents should be careful about what they eat, because
(i) A proper diet develops their brains.
(ii) A 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:

Adolescents should be careful about what they eat because (ii) proper diet is needed for the rapid growth taking place in their bodies.

Q7. Choose the correct option

(b) The reproductive age in women starts when their
(i) menstruation starts.
(ii) Breasts start developing.
(iii) body weight increases.
(iv) height increases.

Answer:

(b) The reproductive age in women starts when their menstruation starts.

Menstruation is the initiation of the reproductive stage in the female.

Q7. Choose the correct option.

(c) The right meal for adolescents consists of
(i) chips, noodles, coke.
(ii) chapati, dal, vegetables .
(iii) rice, noodles and burgers.
(iv) vegetable cutlets, chips and lemon drink.

Answer:

(c) The right meal for adolescents consists of (ii) chapati, dal, and vegetables.

Adolescents should consume a properly balanced diet to compensate for the rapid growth taking place in them.

Q8. Write notes on:

(a) Adam's apple

Answer:

Adam's apple-

At the age of puberty, the voice box or the larynx of humans begins to grow. In the case of boys, it develops larger voice boxes. The developing voice box in boys can be seen as a protruding part of the throat. This protruding part in boys is called the Adam’s apple. In girls, the larynx is small in size so that it can barely be visible from outside.

Q8. Write notes on-

(b) Secondary sexual characters

Answer:

Secondary sexual characters-

Secondary sexual features are those which distinguish males from females, mainly appearing at puberty.

For boys, these include the development of a beard and mustache, the appearance of hair on the chest, and hair development in the pubic area and elsewhere.

For girls, secondary sexual features are an enlargement of the breasts, as well as genital hair development and other body hair.

Q8. Write notes on-

(c) Sex determination in the unborn baby.

Answer:

Sex determination of baby-

Every human being has 46 chromosomes with 23 pairs. Of these, two chromosomes, X & Y, are the sex chromosomes. A woman has two X chromosomes, and a man has one X and one Y chromosome. The female gamete ovum and male gamete sperm have only one set of chromosomes. The unfertilized egg always contains one X chromosome, but sperms may contain two types of chromosomes. They may contain either an X chromosome or a Y chromosome. When the sperm of the X chromosome of the male fertilizes the egg (X chromosome), the zygote would contain two X chromosomes and become a female child. But if the sperm has a Y chromosome and inseminates with the egg (X chromosomes), the zygote would form a male child (XY). Therefore, it is apparent that the gender of an unborn child is established by the sex chromosomes of the father.

Q9. 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
7. Terms for changes at adolescence

Answer:

1. TESTOSTERONE
2. THYROID
3. ADOLESCENCE
4. ENDOCRINE
5. TARGET SITE
6. LYRINX
7. PITUITARY
8. HORMONE
9. INSULIN
10. ESTROGEN

Q10. 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?

Answer:

The graph shows how height and age are related between girls and boys during puberty. At first (ages 4-8), girls are smaller than boys. Girls, though, experience a very fast increase in height when they are 12-16 years old, before their heights settle. The boys, meanwhile, have an acute rise in height at about age 16.