class 8 Reaching the Age of Adolescence Short notes science chapter 10

Puberty

The human body undergoes several changes during adolescence. These changes mark the onset of puberty.

• The most important change, which marks puberty is that boys and girls become capable of reproduction.
• Puberty ends when an adolescent reaches reproductive maturity

Changes at Puberty

Increase in Height

There is a sudden increase in height when one reaches puberty. Long bones grow rapidly, which results in an increase in height. The maximum height is attained by 18 years of age.

Change in Body Shape

Boys become muscular. Their shoulders widen and the waist becomes narrow. The girls widen below the waist and narrow at the shoulders.

Change in Voice

The boys develop a deep and hoarse voice. This happens because the voice box or  the larynx becomes larger. The voice of the girls is usually high-pitched.

The growing voice box in boys can be seen as a protruding part of the throat called Adam’s apple.

In girls, the larynx is hardly visible from the outside because of its small size.

Adam's Apple

Increased Activity of Sweat and Sebaceous Gland

The secretions from the sweat and sebaceous glands increase at this time due to which many teenagers suffer from acne.

Development of Sex Organs

In boys, the testes and penis enlarge and the production of sperms begin. In girls, the ovaries enlarge and start releasing matured eggs.

Secondary sexual characteristics

These are external, visible characteristics that develop in boys and girls after puberty, help to distinguish two sexes and are not directly involved in reproduction. Few of them are as follows.

Boys:

1. The growth of facial hair.
2. The growth of body hair including underarm, abdomen, chest hair and pubic hair.
3. Chest and shoulders widen and body becomes muscular
4. Skin becomes more rough and porous, secretion of sweat glands and sebaceous glands increase
5. Larynx (Adam’s apple)/voice box protrudes out and voice becomes deep and husk.

Girls:

1. Enlargement of breasts
2. The growth of body hair, prominently in the underarm and pubic areas.
3. Widening of hips
4. Changed fat distribution. More fat below the skin, at hips, buttocks and thighs.
5. Development of secondary reproductive organs.

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

• Oestrogen/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 lead 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 onset of the menstrual cycle is called as ‘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 as ‘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.
• But 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.

No Crash Dieting

Personal hygiene

• Personal hygiene is very important, especially during teenage.
• Increased activity of sweat glands sometimes makes the body smelly.
• It also lead 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.

Balance diet for adolescent

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.
• Any teenager 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.

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For more chapters you can follow the link given below

Science Note for Class 8
Chapter 1 Crop Production and Management Class 8 Notes
Chapter 2 Microorganisms: Friend and Foe Class 8 Notes
Chapter 3 Synthetic Fibres and Plastics Class 8 Notes
Chapter 4 Materials: Metals and Non-Metals Class 8 Notes
Chapter 5 Coal and Petroleum Class 8 Notes
Chapter 6 Combustion and Flame Class 8 Notes
Chapter 7 Conservation of Plants and Animals Class 8 Notes
Chapter 8 Cell Structure and Functions Class 8 Notes
Chapter 9 Reproduction in Animals Class 8 Notes
Chapter 10 Reaching the Age of Adolescence Class 8 Notes
Chapter 11 Force and Pressure Class 8 Notes
Chapter 12 Friction Class 8 Notes
Chapter 13 Sound Class 8 Notes
Chapter 14 Chemical Effects of Electric Current Class 8 Notes
Chapter 15 Some Natural Phenomena Class 8 Notes
Chapter 16 Light Class 8 Notes
Chapter 17 Stars and the Solar System Class 8 Notes
Chapter 18 Pollution of Air and Water Class 8 Notes

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