dulingo

NCERT Class 8 Science Chapter 7 ‘Reaching the Age of Adolescence’: Notes and Solutions (Free PDF)

13 minute read
10 shares
Class 8 Science Chapter 7

Well-written notes are of great importance to a student, especially during the exam season. They not only allow the student to cover the chapter in its entirety but also provide a way for easy revision. Hence, keeping these things in mind, we have prepared NCERT Solutions and Notes for Class 8 Science Chapter 7: Reaching the Age of Adolescence. These notes are written in a point-wise manner. After the notes, you will also find the solutions to NCERT textbook questions. A PDF of the same is also available for you to download. Now, let’s explore this blog. 

Chapter 1Chapter 2Chapter 3
Chapter 4Chapter 5Chapter 6
Chapter 7Chapter 8Chapter 9
Chapter 10Chapter 11Chapter 12
Chapter 13

Class 8 Science Chapter 7 Reaching the Age of Adolescence: Adolescence and Puberty Notes

In this chapter, you will learn about the phases of adolescence and puberty with the roles of hormones in both of them let’s start with the notes. 

Adolescence and Puberty

That phase of life when the body changes to reach reproductive maturity is known as adolescence. It begins at around the age of 11 and goes up to the age of 18 and 19. 

In girls, it may start a year or two earlier than the boys. 

The changes that the body goes through during the adolescent years mark the onset of puberty. The phase of puberty ends when the adolescent phase reaches reproductive maturity. 

Several changes take place during puberty. Let’s look at them individually.

Increase in Height

  • At puberty there is a sudden increase in height this is because during this time, the bones of the arms and legs elongate. 
  • Initially, girls grow faster than boys but by about 18 years of age, both reach their maximum height.
  • The rate of growth varies in boys and girls. 
  • Height depends on the genes inherited from the family.
  • During this phase, the right diet is also necessary.

Change in Body Shape

  • Boys’ shoulders broaden.
  • In girls, the region below the waist becomes wider.
  • In boys, the muscles of the body grow more prominently than in girls.

Voice Change

  • The voice box or the larynx starts growing during puberty.
  • The vice box in boys becomes more prominent and can be seen as a protruding part of the throat called Adam’s apple
  • Girls have a high-pitched voice, whereas boys have a deep voice.
Class 8 Science Chapter 7: Reaching the Age of Adolescence: Larynx

Increased Activity of Sweat and Sebaceous Glands

  • During puberty, the secretion of sweat glands and sebaceous glands (oil glands) increases.
  • Pimples and acne also appear on the face.

Development of Sex Organs

  • At puberty, male sex organs like the testes and penis develop completely.
  • The testes also begin to produce sperm.
  • In girls, the ovaries enlarge and eggs begin to mature. Also, ovaries start releasing mature eggs

Reaching Mental, Intellectual and Emotional Maturity

  • Adolescents become self-conscious.
  • It is often the time in one’s life when the brain has the greatest capacity for learning.
  • They may also feel insecure.
  • These changes are a natural part of growing up.

Also Read: 100 Branches of Biology from A to Z

Source: Magnet Brains

Class 8 Science Chapter 7 Reaching the Age of Adolescence: Secondary Sexual Characters Notes

In this section, we will learn about the development and role of secondary sexual characters. Let’s begin.

  • The characters that help in distinguishing males from females are known as secondary sexual characters.
  • Boys begin to grow facial hair. They also grow hair on the chest.
  • In girls, breasts begin to develop at puberty.
  • In both, boys and girls, hair grows under the arms and in the region above the thighs or the pubic region.
  • These changes are controlled by the hormones that are chemical substances and are secreted by endocrine glands or the endocrine system.
  • Endocrine glands are the ones that secrete hormones directly into the bloodstream. They are also known as ductless glands.
  • Testosterone is the male hormone that is released by the testes at the onset of puberty.
  • Estrogen is the female hormone and is released by the ovaries. They lead to the development of breasts. 
  • Milk-secreting glands or mammary glands develop inside the breasts.

Role of Hormones in Initiating Reproductive Function

Hormones secreted by the endocrine glands reach a specific body part known as the target site that responds to the hormones.

  • The pituitary, which is an endocrine gland, secretes a hormone that controls the secretion of testosterone and estrogen.
  • The sequence of this process is as follows:- hormones from the pituitary stimulate the testes and ovaries to produce testosterone and estrogen → these hormones are released in the bloodstream and reach the target site → they stimulate changes in the body on the onset of puberty.

Reproductive Phase of Life in Humans

Here are some key facts about the reproductive phase of human lives:

  • In females, the reproductive phase of life begins at puberty (10 to 12 years of age) and generally lasts till the age of approximately 45 to 50 years.
  • With the onset of puberty, ova begin to mature. One ovum is released by one of the ovaries once in about 28-30 days.
  • During this, the uterine walls start to become thick, to receive and nourish the egg in case of fertilisation.
  • In case it is fertilised and begins to develop.
  • 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
  • Menstruation occurs once in about 28 to 30 days. 
  • The first menstrual flow begins at puberty and is termed menarche.
  • At 45 to 50 years of age, the menstrual cycle stops. Stoppage of menstruation is termed menopause

How is the Sex of the Baby Determined?

Now, let us understand factors and processes determining the sex of an infant:

  • Thread-like structures that are present inside the nucleus of every cell are known as chromosomes.
  • All human beings have 23 pairs of chromosomes in the nuclei of their cells out of which 22 are autosomes and one is a pair of sex chromosomes i.e. X and Y. 
  • A female has two X chromosomes, while a male has one X and one Y chromosome. 
  • The gametes (egg and sperm) have only one set of chromosomes. 
  • The unfertilised egg always carries an X chromosome but the sperm may carry an X or a Y chromosome.
  • Now, during fertilisation, if a sperm carrying an X chromosome fertilises the egg, then the zygote formed would contain two X chromosomes. Such a zygote would develop into a female.
  • If a sperm carrying a Y chromosome fertilises the egg, then the resulting zygote will have an X and a Y chromosome. Such a zygote would develop into a male.
  • Hence, it would be correct to say that the gender of the baby is determined by the father. 
Class 8 Science Chapter 7: Reaching the Age of Adolescence: Sex of the Baby

Hormones other than Sex Hormones

Apart from the pituitary, the testes and the ovaries, there are other endocrine glands in the body such as the thyroid, pancreas and adrenals.

  • The thyroid gland produces the hormone thyroxine. Deficiency of this hormone can lead to a disease called goitre in which the throat swells up and bulges. 
  • The pancreas produces insulin hormone that regulates the sugar levels in the blood. The malfunction of the pancreas can lead to a disease called diabetes
  • The adrenal glands secrete adrenaline. It helps the body to adjust to stress when one is very angry, embarrassed or worried. It is also known as the fight or flight hormone.
  • The pituitary also secretes growth hormone which is necessary for the normal growth of a person.
Class 8 Science Chapter 7: Reaching the Age of Adolescence: Endocrine Glands

Role of Hormones in Completing the Life History of Insects and Frog

  • Insect hormones control metamorphosis in insects.
  • In a frog, it is controlled by thyroxine, the hormone produced by the thyroid.
  • Thyroxine production requires the presence of iodine in water. If the water in which the tadpoles are growing does not contain sufficient iodine, the tadpoles cannot become adults.

Also Read: Branches of Zoology: Specialisations, Programs & More

Class 8 Science Chapter 7 Reaching the Age of Adolescence: Reproductive Health Notes

This section focuses on how to maintain reproductive health. The role of diet, personal hygiene and exercise is also covered in the same. Let’s have a look at it.

Nutritional Needs of the Adolescent

A balanced diet is one that includes proteins, carbohydrates, fats and vitamins in requisite proportions.

  • Iron builds blood and iron-rich food such as leafy vegetables, jaggery, meat, citrus, and Indian gooseberry (amla) are good for adolescents
  • Chips and packed or tinned snacks, though very tasty should never replace regular meals as they do not have adequate nutritional value.

Also Read: Essay on Food for School Students: 100, 200, 300 Words

Class 8 Science Chapter 7: Reaching the Age of Adolescence: Balanced Diet

Personal Hygiene

Here are some key points about the personal hygiene of girls:

  • Girls should take special care of cleanliness during the time of menstrual flow. They should keep track of their menstrual cycle and be prepared for the onset of menstruation
  • Use sanitary napkins or clean homemade pads. Change pads after every 4–5 hours as per the requirement.

Also Read: Impact of Personal Hygiene on Student’s Well-being

Say “NO” to Drugs

Drugs are addictive. If you take them once, you feel like taking them again and again. They harm the body in the long run. Just say ‘No’ unless prescribed by the doctor. Drugs are addictive. If you take them once, you feel like taking them again and again. They harm the body in the long run. 

Also Read: How to Become a Drug Inspector?

Important Definitions in NCERT Class 8 Science Chapter 7: Reaching the Age of Adolescence

Here are the important definitions in Class 8 Science Chapter 7 Reaching the Age of Adolescence:

  • Adolescence: That phase of life when the body changes to reach reproductive maturity is known as adolescence.
  • Secondary Sexual Characters: The characters that help in distinguishing males from females are known as secondary sexual characters.
  • Endocrine Glands: Endocrine glands are the ones that secrete hormones directly into the bloodstream. They are also known as ductless glands.
  • Menstruation: 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. 
  • Menarche: The first menstrual flow begins at puberty and is termed menarche.
  • Menopause: At 45 to 50 years of age, the menstrual cycle stops. Stoppage of menstruation is termed menopause. 
  • Chromosome: Thread-like structures that are present inside the nucleus of every cell are known as chromosomes.
Chapter 1Chapter 2Chapter 3
Chapter 4Chapter 5Chapter 6
Chapter 7Chapter 8Chapter 9
Chapter 10Chapter 11Chapter 12
Chapter 13

NCERT Solutions of Class 8 Science  Chapter 7: Reaching the Age of Adolescence

Let us now explore NCERT Solutions of Class 8 Science Chapter 7 to get answers to all writing

questions in the lesson Reaching the Age of Adolescence.

Exercise Questions

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

Soln:

Hormones are chemical substances that are secreted by endocrine glands or the endocrine system. They are responsible for the changes taking place in the body.

2. Define adolescence.

Soln:

That phase of life when the body changes to reach reproductive maturity is known as adolescence. It begins at around the age of 11 and goes up to the age of 18 and 19. 

In girls, it may start a year or two earlier than the boys. The changes that the body goes through during the adolescent years mark the onset of puberty. The phase of puberty ends when the adolescent phase reaches reproductive maturity. 

3. What is menstruation? Explain.

Soln:

  • In females, the reproductive phase of life begins at puberty (10 to 12 years of age) and generally lasts till the age of approximately 45 to 50 years.
  • With the onset of puberty, ova begin to mature. One ovum is released by one of the ovaries once in about 28-30 days.
  • During this, the uterine walls start to become thick, to receive and nourish the egg in case of fertilisation.
  • In case it is fertilised and begins to develop.
  • 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
  • Menstruation occurs once in about 28 to 30 days. 
  • The first menstrual flow begins at puberty and is termed menarche.
  • At 45 to 50 years of age, the menstrual cycle stops. Stoppage of menstruation is termed menopause

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

Soln:

Several changes take place during puberty. They are mentioned as follows:-

Increase in Height

  • At puberty there is a sudden increase in height this is because during this time, the bones of the arms and legs elongate.
  • The rate of growth varies in boys and girls. 
  • Height depends on the genes inherited from the family.

Change in Body Shape

  • Boys’ shoulders broaden.
  • In girls, the region below the waist becomes wider.
  • In boys, the muscles of the body grow more prominently than in girls.

Voice Change

  • The voice box or the larynx starts growing during puberty.
  • The vice box in boys becomes more prominent and can be seen as a protruding part of the throat called Adam’s apple
  • Girls have a high-pitched voice, whereas boys have a deep voice.

Increased Activity of Sweat and Sebaceous Glands

  • During puberty, the secretion of sweat glands and sebaceous glands (oil glands) increases.
  • Pimples and acne also appear on the face.

Development of Sex Organs

  • 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

  • Adolescents become self-conscious.
  • It is often the time in one’s life when the brain has the greatest capacity for learning.
  • They may also feel insecure.
  • These changes are a natural part of growing up.

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

Soln:

Endocrine GlandsHormones
TestisTestosterone
OvaryOestrogen
PituitaryGrowth hormone
AdrenalAdrenalin
PancreasInsulin
ThyroidThyroxin

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

Soln:

Sex hormones are those chemical substances that are produced by the sex organs that are responsible for the development of secondary sexual characteristics that appear during puberty.  

In males, the testes produce the hormone testosterone. It helps in the development of secondary sexual characteristics such as facial hair, hoarse voice, broad shoulders, etc.

In females, the ovaries produce estrogen. It helps in the development of secondary sexual characteristics such as the development of breasts, onset of menstrual cycle, high-pitched voice, etc.

7. Choose the correct option.

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

(i) 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.

(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.

Soln:

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

b) (i) menstruation starts.

c) (ii) chapati, dal, vegetables.

8. Write notes on—

(a) Adam’s apple.

(b) Secondary sexual characters.

(c) Sex determination in the unborn baby.

Soln:

a) Adam’s apple: The voice box or the larynx starts growing during puberty.

The voice box in boys becomes more prominent and can be seen as a protruding part of the throat called Adam’s apple. This is because of the sex hormones, hence making the vocal cords thicker and longer, which causes the voice to become hoarse. On the other hand, in females, the larynx is small and hardly visible. Hence,  girls have a high-pitched voice while boys have a deep voice.

b) Secondary sexual characters: Sex hormones are those chemical substances that are produced by the sex organs that are responsible for the development of secondary sexual characteristics that appear during puberty.  

In males, the testes produce the hormone testosterone. It helps in the development of secondary sexual characteristics such as facial hair, hoarse voice, broad shoulders, etc.

In females, the ovaries produce estrogen. It helps in the development of secondary sexual characteristics such as the development of breasts, onset of menstrual cycle, high-pitched voice, etc.

c) Sex determination in the unborn baby: All human beings have 23 pairs of chromosomes in the nuclei of their cells out of which 22 are autosomes and one is a pair of sex chromosomes i.e. X and Y. A female has two X chromosomes, while a male has one X and one Y chromosome. The gametes (egg and sperm) have only one set of chromosomes. The unfertilised egg always carries an X chromosome but the sperm may carry an X or a Y chromosome. Now, during fertilisation, if a sperm carrying an X chromosome fertilises the egg, then the zygote formed would contain two X chromosomes. Such a zygote would develop into a female. If a sperm carrying a Y chromosome fertilises the egg, then the resulting zygote will have an X and a Y chromosome. Such a zygote would develop into a male.

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

Soln:

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

CBSE Notes Class 8 EnglishCBSE Notes Class 8 History CBSE Notes Class 8 Geography
CBSE Notes Class 8 CivicsCBSE Notes Class 8 MathematicsCBSE Notes Class 8 Science

FAQs

Q1. What are the ages of adolescence?

Ans: The adolescent age starts from 11 years and continues till 19 years.

Q2. What is menstruation?

Ans: 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.

Q3. What are hormones in Class 8 notes?

Ans: Hormones are chemical substances that are secreted by endocrine glands or the endocrine system.

Follow Leverage Edu for complete study material on CBSE Notes of Class 8 Science

Leave a Reply

Required fields are marked *

*

*