Class 8 Science Chapter 7: Reaching the Age of Adolescence

Introduction to Reaching the Age of Adolescence:

These notes of Reaching the Age of Adolescence cover the entire chapter comprehensively for quick revision. Practice all NCERT questions and in-text activities for better marks!

1. Adolescence and Puberty

• Adolescence: The period of life when the body undergoes major changes leading to reproductive maturity. It begins around the age of 11 and lasts up to 18 or 19 years.
• Puberty: The phase during adolescence when reproductive organs become functional and sexual maturity is reached.
• Adolescence is a bridge between childhood and adulthood.
• The onset of puberty varies among individuals. Girls generally reach puberty earlier than boys.

2. Age of Onset

• In girls: Puberty usually starts between 10–13 years (often around 11 years).
• In boys: Puberty usually starts between 11–14 years (often around 13 years).
• The entire process of puberty takes about 3–5 years to complete.

3. Changes at Puberty

A. Increase in Height

• The most noticeable change is sudden increase in height.
• Growth is maximum during the early years of puberty; later it slows down.
• Long bones (bones of arms and legs) elongate.
• Girls grow faster initially; boys have a longer growth period, so they often become taller than girls.

B. Change in Body Shape

• Boys: Shoulders become broader, chest widens.
• Girls: Hips become wider, pelvis broadens for future childbirth.

C. Voice Change

• In boys: Voice box (larynx) grows larger → voice becomes deep and hoarse (voice “cracks”).
• In girls: Larynx grows slightly → voice becomes slightly shrill but not as deep as boys.

D. Increased Activity of Sweat and Sebaceous (Oil) Glands

• Leads to more sweating and body odour.
• Causes acne and pimples on the face due to excess oil secretion.

E. Development of Secondary Sexual Characters These are features that help distinguish males from females but are not directly involved in reproduction.

F. Development of Sex Organs (Primary Sexual Characters)

• In boys: Testes enlarge, start producing sperms; penis becomes longer.
• In girls: Ovaries enlarge, start releasing mature eggs; menstruation begins.

4. Reproductive Phase of Life

• In females: From about 11–45/50 years (menarche to menopause).
  • Menarche: The first menstrual flow (usually between 10–15 years).
  • Menopause: Stoppage of menstruation (usually around 45–50 years).
  • Menstrual cycle occurs roughly every 28–30 days.
• In males: From about 13–14 years onwards till old age. Sperm production continues throughout life.

5. Hormones and Their Role

• Hormones are chemical messengers secreted directly into the blood by endocrine glands.
• Pituitary Gland (master gland) secretes hormones that stimulate testes (in boys) and ovaries (in girls) to release sex hormones.
• Sex hormones:
  • In boys: Testosterone (produced by testes).
  • In girls: Estrogen and Progesterone (produced by ovaries).
• These hormones cause all the changes of puberty and development of secondary sexual characters.

6. Role of Hormones in Girls (Menstrual Cycle – Simplified)

• Ovary releases one mature egg roughly every month.
• Uterus lining thickens to receive the fertilized egg.
• If fertilization does not occur → thickened lining along with blood vessels is shed → menstruation (periods).
• Duration of menstrual flow: 3–5 days.
• Cycle length: Usually 28–30 days (can vary).

7. Determination of Sex of the Baby

• Human beings have 23 pairs of chromosomes (46 total).
• 22 pairs are autosomes; 1 pair is sex chromosomes.
• Females: XX (homogametic)
• Males: XY (heterogametic)
• All eggs carry X chromosome.
• Sperm can carry either X or Y.
  • Sperm with X + Egg (X) → XX → Baby girl
  • Sperm with Y + Egg (X) → XY → Baby boy
• Therefore, the sex of the baby is determined by the father.

8. Endocrine Glands Involved in Puberty

• Pituitary gland: Stimulates other glands.
• Thyroid gland: Produces thyroxine (regulates metabolism and growth).
• Adrenal glands: Secrete adrenaline and other hormones.
• Testes (in boys): Testosterone.
• Ovaries (in girls): Estrogen and progesterone.
• Pancreas: Insulin (though not directly related to puberty, important for overall growth).

9. Nutritional and Health Needs of Adolescents

• Adolescents need a balanced diet rich in:
  • Proteins (for growth and repair)
  • Carbohydrates and fats (for energy)
  • Iron (especially girls due to menstruation)
  • Calcium and Vitamin D (for strong bones)
  • Iodine (thyroxine production)
• Deficiency of iron → anaemia (common in girls).
• Regular exercise is essential for proper muscle and bone development.

10. Personal Hygiene During Adolescence

• Bath daily to avoid body odour.
• Change undergarments daily.
• Girls should keep menstrual hygiene:
  • Use sanitary pads or menstrual cups.
  • Change pads every 4–6 hours.
  • Wash genital area properly.
• Clean face regularly to prevent acne.
• Avoid sharing towels/combs to prevent infections.

11. Emotional and Mental Changes

• Mood swings due to hormonal changes.
• Attraction towards opposite sex.
• Desire for independence.
• Confusion and anxiety about body changes.
• Peer pressure increases.
• Adolescents need emotional support from parents/teachers.

12. Myths and Misconceptions

• Myth: Masturbation causes physical weakness or infertility → Scientifically false.
• Myth: Menstruating girls are impure → Menstruation is a natural process.
• Myth: Boys should not cry → Emotions are natural for both genders.

13. Say “No” to Drugs

• Adolescence is the time when many start experimenting with tobacco, alcohol, and drugs due to peer pressure.
• These are addictive and harmful to health.
• Drugs affect brain development and can lead to serious diseases.

14. AIDS (Acquired Immuno Deficiency Syndrome)

• Caused by HIV (Human Immunodeficiency Virus).
• Spreads through:
  • Unprotected sexual contact
  • Infected blood transfusion
  • Infected mother to child during pregnancy/birth/breastfeeding
  • Sharing infected needles
• No cure yet, but can be managed with medicines (ART).
• Prevention: Safe sex, screened blood, avoid sharing needles.

Important Diagrams to Practice

1. Male and female reproductive systems
2. Location of major endocrine glands
3. Changes in height graph (boys vs girls)
4. Menstrual cycle (simplified)

Key Points for Exams

• Puberty ends when an adolescent reaches reproductive maturity.
• Testosterone → male hormone; Estrogen → female hormone.
• Adam’s apple is prominent in boys.
• Menarche is the beginning; menopause is the end of menstruation.
• Sex of the child is determined by the father’s sperm (X or Y).

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