Class-8, Science,Chapter:- 10 Reaching The Age of Adolescence Notes, NCERT Solutions & Frequently Asked Questions

 Science

Class:-8, Chapter:- 10

Reaching The  Age of Adolescence 

Notes, NCERT Solutions & Frequently Asked Questions

-- Notes --

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

• This is the time span in which the child develops into an adult.

• Adolescence begins around the age of 11 and goes on until 18 or 19 years of age.

•  Children between the age of 11 to 19 years are called Adolescents or teenagers.

• The body at this stage undergoes important changes and these mark the period of puberty.

⭐Puberty:- Puberty is the period, during which, the human body undergoes certain changes in their body and reproductive organs which leads to sexual maturity.

• The most important change, which marks puberty is that boys and girls become capable of reproduction.

• In girls, puberty may begin a year or two earlier than in boys.

⭐ Changes at Puberty:- An individual goes through different changes during the onset of puberty.

• It differs in males and females, also the extent of these changes is different in each person.

• Each individual goes through changes like increase in height, change in body shape, change in voice, development of sex organs, mental, intellectual and emotional maturity.

⭐ Secondary sexual characteristics:- These are external, visible characteristics that develop in boys and girls after puberty & helps to distinguish the two sexes and are not directly involved in reproduction. A 

👉 Secondary  sexual characteristics of Boys:-

• Growth of facial hair.

• Growth of body hair including underarm, abdomen, chest hair and pubic hair.

• Chest and shoulders widen and body becomes muscular. 

• Skin becomes more rough and porous, secretion of sweat glands and sebaceous glands increase. 

• Larynx (Adam’s apple)/voice box protrudes out and voice becomes deep and husk.

👉 Secondary sexual characteristics of Girls:-

• Enlargement of breasts. 

• Growth of body hair, prominently in the underarm and pubic areas.

• Widening of hips. 

• Changed fat distribution. More fat below the skin, at hips, buttocks and thighs.

• Development of secondary reproductive organs.

⭐ Mental and Physical Changes at Puberty:-

• Reproductive health:- The physical and mental well being of an individual is regarded as an individual’s health.

• During adolescence, the reproductive organs develop and become functional.

• Reproductive health means proper growth and well being of the reproductive organs.

⭐ Endocrine glands:- An endocrine system is a group of ductless glands that regulate body processes and functioning of many systems by secreting chemical substances called hormones.

• They release their secretions directly into the bloodstream.

• The origin and site of action are usually distant for hormones.

• Endocrine glands release hormones into the bloodstream to reach a particular body part fraction called Target Site.

⭐ Hormones:- Hormones are chemical messengers secreted by the endocrine glands.

• They control body functioning, physiology and behaviour.

⭐ Pituitary gland:- The pituitary gland is situated in the brain and is called a master endocrine gland.

• It produces hormones that instruct other glands to secrete their hormones.

• The pituitary gland secretes growth hormone which controls the overall growth of a person.

• Secretion of growth hormone is maximum in adolescence period.

⭐ Testosterone:- Testosterone is the primary male sex hormone.

• It is responsible for the development of the male reproductive organs, production of male gamete i.e. sperms and development of secondary sexual characteristics too.

• Testes start secreting testosterone only after puberty.

⭐ Oestrogen:- Estrogen/oestrogen is the primary female sex hormone.

• It is responsible for the development of the female reproductive organs, production of female gamete i.e. ova and development of secondary sexual characteristics and menstrual cycle.

• Ovaries secrete this hormone after puberty.

⭐ Thyroid gland:- It is a butterfly-shaped gland situated in the throat.

• It secretes a hormone called thyroxin.

• This hormone is important as it maintains the balance of all metabolic activities.

• The deficiency of this hormone can cause swelling of the thyroid gland, leading to goitre.

⭐ Pancreas:- The pancreas secretes a hormone called insulin, which regulates the blood sugar level in the body.

• Deficiency of insulin leads to diabetes.

⭐ Adrenal glands:- The adrenal glands are situated right above the kidneys.

• They change their shape throughout life and shrink as a person grows older.

• They secrete a hormone adrenaline and also maintain the salt and pH balance.

• Hormone adrenaline is also called ‘fight or flight’ hormone as it functions in emergency situations.

⭐ Menstrual Cycle:- It is a reproductive cycle of females.

• It begins at puberty and the starting of the menstrual cycle is called ‘menarche’.

• The process includes cyclic changes in the ovaries and in the uterus, both simultaneously.

• In the ovaries, an ovum develops and matures and then released.

• In the uterus, a thick spongy inner lining develops anticipating pregnancy.

• If the egg is fertilized, pregnancy occurs.

• 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.

• The menstrual cycle stops in women anywhere between 45 to 52 years.

• Stopping of the menstrual cycle is called ‘menopause‘.

• The years between menarche and menopause marks the reproductive age of a woman where she is able to bear a child.

⭐ Boy or Girl/Sex Determination:- All human beings have 23 pairs of chromosomes in the nuclei of their cells.

• Two chromosomes out of these are of 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 have only one set of chromosomes.

• The unfertilised ovum always has one X chromosome.

• In the male gametes or sperms, there exists one kind having an X chromosome and the other kind having a Y chromosome.

• When a sperm containing X chromosome fuses with an egg, it develops into a female child.

• When a sperm containing Y chromosome fuses with an egg, it develops into a male child.

⭐ Personal hygiene:- Personal hygiene is very important, especially during teenage years.

• Increased activity of sweat glands sometimes makes the body smelly.

• It also leads to acne.

• All parts of the body should be washed and cleaned every day.

• If cleanliness is not maintained there are chances of catching bacterial and fungal infections.

⭐ Balanced diet:- Adolescence also equates to a sudden spurt in growth of the body.

• A growing body requires all the nutrients.

• Therefore, all the teenagers should consume a balanced diet and not junk food.

• A balanced diet is a meal that includes proteins, carbohydrates, fats and vitamins in proper proportions.

• Junk food affects the growth of an individual.

⭐ Physical exercise:- Exercise ensures a healthy body and mind.

• Walking, playing or practising yoga are some of the many ways we can carry out physical exercise.

⭐ Say NO to Drugs:- Drugs are addictive and harm the body in long term.

• Sometimes harm done by drugs becomes irreversible.

• All teenagers should say ‘NO’ to drugs.

• HIV can pass on to a normal person from an infected person by sharing the syringes used for injecting drugs.

• It can also be transmitted to an infant from the infected mother through her milk.

• The virus can also be transmitted through sexual contact with a person infected with HIV.

• People who are addicted to drugs have more chance of having HIV infection.

-- NCERT Solutions --

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

Solution:- The chemical substance secreted by the endocrine glands is called Hormones. Hormones are responsible for the changes taking place in the body.

Question 2.- Define adolescence.

Solution:- The time period which comes between the beginning of adulthood and puberty is called Adolescence. In this time period, the body undergoes different changes alongside reproductive maturity. It starts somewhat at the age of 11 and ends at the age of 18 or19. This period of adolescence may differ from person to person.

Question 3.- What is menstruation? Explain

Solution:- The process of shedding of the uterine lining on a regular monthly basis is called menstruation. It starts at puberty and in the reproductive cycle of the female body. The uterus prepares itself to receive a fertilized egg on every month. Due to this the inner lining of the uterus become thick and is supplied with blood to nourish the embryo. If the egg is not fertilized, then the lining of the uterus breaks down and get released in the form of blood through the vagina. The time period for this is about 2 to 8 days every month. This monthly cycle is known as the menstrual cycle.

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

Solution:- The changes that take place at the time of puberty are as follows:-

a) The height and weight of the body will suddenly increases. 

b) The hair seems to appear in the areas such as legs, hands, face, underarms & genital areas. 

c) In female, the enlargement of the ovary & breast takes place and starts producing matured eggs and on the other hand in males, the testis grows and starts producing sperms. 

d) In males, the shoulder broadens and chest becomes wider, whereas in females the region below the waist becomes wider.

e) Acne seems to appear because of the excessive secretion of the oil from the skin.

f) In boys, the larynx becomes prominent under the influence of hormones, the vocal cord becomes longer and thicker resulting in a hoarse voice.

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

Solution:-

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

Solution:- The chemical substances produced by the sex organs are called sex hormones. For example, in females, the sex hormones produced by the ovary is called oestrogen and in males, the sex hormones produced by the testis is called testosterone. Some of the functions performed by the sex hormones:

• Oestrogen:- This hormone is responsible for the development of secondary sexual characters in females like enlargement of breasts, development of female reproductive organs, etc.

• Testosterone:- This hormone brings the secondary sex character in boys such as the growth of beard, the voice becomes hoarse, development of the reproductive organs 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.

(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.

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

b) (i) menstruation starts.

c) (ii) chapati, dal, vegetables.

Question 8.- Write notes on—

(a) Adam’s apple.

(b) Secondary sexual characters.

(c) Sex determination in the unborn baby.

Solution:- 

a) Adam’s apple:- In human males, the larynx grows larger at the time of puberty and can be seen as a protruding part of the throat. This protrusion is known as Adam’s apple. In boys under the influence of sex hormones, the larynx becomes prominent. Due to this, the vocal cord becomes thicker and longer which causes the voice hoarse. On the other hand in females, the larynx is of small size and is hardly visible. Therefore, girls have a high pitched voice while the boys have a deep voice.

b) Secondary sexual characters:- Characters which usually appear during the phase of puberty are called as secondary sexual characters. These are the features that help in distinguishing the male and female body from each other.

  • Characters seen in male:- Hoarseness of voice, appearance of beard, broadness of chest, growth of hair in genital areas.

  • Characters seen in female:- Start of menstrual cycle, growth of breast, growth of hair in the genital areas.

c) Sex determination in the unborn baby:- Sex of a unborn baby depends upon the pair of sex chromosomes that are present in the cells of the baby.

X and Y chromosomes are the sex chromosomes in humans. Ovum always contain X chromosome, male sperm may carry either X chromosome or Y chromosome. Male genetic make-up is 44 autosomes + XY chromosome and female genetic make-up is 44 autosomes + XX chromoses.

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 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

Solution:-

Across

3. Adam’s apple

4. Endocrine

7. Pituitary

8. Hormone

9. Insulin

10. Estrogen

Down

1. Testosterone

2. Thyroid

3. Adolescence

5. Target site

6. Larynx

7. Puberty

-- Frequently Asked Questions --

Question 1.- Define puberty.

Solution:- The process by which a child's body evolves into an adult body and achieves sexual maturity is known as puberty. With most children it occurs generally around 10-12 years of age.

Question 2.- What is Adam's apple?

Solution:- At puberty, a bigger voice box develops in boys, which can be seen as a projecting region of the throat. This is referred to as Adam's apple.

Question 3.- Define hormones.

Solution:- Hormones are chemical substances produced by the endocrine glands.

Question 4.- Define adolescence.

Solution:- Adolescence is the stage of life when the body experiences changes that lead to reproductive maturity. Adolescence begins around the age of eleven and lasts until the age of eighteen or nineteen.

Question 5:- What are secondary sexual characters?

Solution:- Secondary sexual traits are characteristics that help distinguish a man from a woman. For example, boy’s moustaches and beards, and development of breasts in females.

Question 6:- Which hormones help in the development of secondary sexual characters?

Solution:- In males and females, testosterone and estrogens respectively aid in the development of secondary sexual characteristics.

Question 7:- What is pituitary gland? Name the hormones secreted by it?

Solution:- The pituitary gland is an endocrine gland that regulates the activity of all other glands in the body. Some of the hormones secreted by pituitary gland are as follows:

• Growth Hormones

• Prolactin

• Thyroid-stimulating hormone, etc.

Question 8:- What do you mean by target site?

Solution:- Endocrine glands secrete hormones into the bloodstream in order for them to reach a specific body part known as a target site. Target sites respond to hormones in various ways.

Question 9:- Write a short note on the reproduction phase in humans.

Solution:- When adolescent’s testes and ovaries begin to create gametes in males and females respectively, they are able to reproduce. Males have a substantially longer capability for maturation and the creation of gametes than females. The reproductive period of females begins in puberty at the age of 10 to 12 years and lasts until about 45 to 50 years of age. The reproductive phase of males begins in puberty at the age of 11 to 13 years and lasts a lifetime.

Question 10:- What do you mean by: 

a) Menstruation

b) Menarche

c) Menopause

Solution:-

a) Menstruation:- Normal vaginal bleeding that happens as part of a woman's monthly cycle is known as menstruation, or period. Your body prepares for pregnancy every month. The uterus or womb removes its lining if no pregnancy develops. Menstrual blood is a mixture of blood and tissue from the uterus.

b) Menarche:- The first menstrual cycle in a female adolescent is known as menarche.

c) Menopause:- Menopause is the term used to describe the end of a woman's menstrual cycle. Menopause could hit in the forties or fifties.

- By Durgesh Pandey