SCIENCE

Reaching the Age of Adolescence – NCERT Class 8 Full Summary

Adolescence is the period of life when a child undergoes physical, emotional, and hormonal changes, transitioning into adulthood. This phase typically begins around the age of 11 and lasts until 18 or 19 years.

1. Adolescence and Puberty

• Adolescence: The phase of rapid growth and development between childhood and adulthood.

• Puberty: The stage during adolescence when the body undergoes changes leading to reproductive maturity.

Changes During Puberty

Puberty brings about several physical, emotional, and psychological changes due to hormonal activity.

2. Changes at Puberty

A. Physical Changes

1. Increase in Height

   • Growth in bones and muscles leads to an increase in height.

   • Boys grow taller than girls on average.

2. Change in Body Shape

   • Boys: Broad shoulders, muscular body.

   • Girls: Wider hips, increased fat deposition.

3. Voice Changes

   • Boys: Voice deepens as the larynx (voice box) enlarges.

   • Girls: Voice remains soft, with minor changes.

4. Increased Activity of Sweat and Sebaceous Glands

   • Leads to pimples and acne due to more oil (sebum) production.

5. Growth of Hair

   • Hair develops in armpits, pubic areas, chest (boys), and face (boys).

B. Secondary Sexual Characteristics

These are features that distinguish males and females but are not directly involved in reproduction.

• Boys: Growth of facial and chest hair, deep voice.

• Girls: Development of breasts, broader hips.

3. Role of Hormones in Puberty

Hormones control puberty and sexual development.

• Testosterone (Male Hormone): Produced by testes, responsible for male puberty changes.

• Estrogen (Female Hormone): Produced by ovaries, responsible for female puberty changes.

The pituitary gland in the brain signals the release of these hormones.

4. The Reproductive Phase of Life

• Boys: Begin sperm production from puberty and continue throughout life.

• Girls: Start menstruation, indicating reproductive maturity.

Menstrual Cycle (In Girls)

• Occurs approximately every 28–30 days.

• The ovary releases an egg (ovulation).

• If fertilization does not occur, the uterine lining sheds as menstrual blood (lasting 3–7 days).

• This continues until menopause (around 45–50 years of age).

5. Determination of Sex in a Baby

• The sex of a baby is determined by chromosomes in sperm and egg.

• Humans have 23 pairs (46 total) of chromosomes.

• The 23rd pair determines gender:

  • XX = Female

  • XY = Male

• The father’s sperm decides the sex of the baby.

6. Hormones Other Than Sex Hormones

• Growth Hormone: Controls height and body growth.

• Thyroxine: Produced by the thyroid gland, controls metabolism.

• Insulin: Regulates blood sugar levels.

• Adrenaline: Prepares the body for stress and emergencies.

7. Healthy Adolescence Habits

• Balanced Diet: Essential for proper growth and development.

• Personal Hygiene: Helps prevent infections (e.g., regular bathing, changing undergarments).

• Regular Exercise: Keeps the body fit and strengthens muscles.

• Avoiding Harmful Substances: Stay away from drugs, alcohol, and tobacco.

8. Adolescence and Mental Well-Being

• Emotional changes lead to mood swings, stress, and peer pressure.

• It’s important to express feelings, communicate openly, and maintain self-confidence.

This summary covers the Class 8 NCERT Chapter – Reaching the Age of Adolescence in detail. Let me know if you need any clarifications! 😊