Introduction

Adolescence is the stage of life between childhood and adulthood. It usually happens between the ages of 11 and 19. Children at this age are called teenagers because these years fall in the “teens.” During this period, the body becomes capable of reproduction and undergoes many physical, emotional, and mental changes.

Changes at Puberty

Growth and Height

One of the most noticeable changes during puberty is a sudden increase in height. This happens because the long bones of arms and legs grow quickly. Growth is not uniform, so some body parts may seem out of proportion at first, but it balances over time.

Change in Body Shape

• Boys: Shoulders and chest become broader; muscles develop more strongly.

• Girls: Hips widen, and the body takes on a rounded shape.
  These differences are normal and lead to gender-specific characteristics.

Voice Change

• In boys, the voice box (larynx) grows larger, making their voices deeper. Voice “cracking” may happen during this phase.

• In girls, the voice may change slightly, but not as much as in boys.

Sweat and Oil Glands

Sweat glands and sebaceous (oil) glands become more active, leading to increased sweating and sometimes acne. Both boys and girls also develop body hair, such as underarm and pubic hair. Boys may also grow beards and mustaches.

Development of Sex Organs

• Boys: Testes and penis develop fully, and the testes begin producing sperm.

• Girls: Ovaries enlarge, eggs mature, and ovulation begins. This marks the start of reproductive capability.

 

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Role of Hormones

Hormones control most changes during puberty. The pituitary gland in the brain releases hormones that signal the testes in boys to produce testosterone and the ovaries in girls to produce estrogen. These sex hormones drive the physical and reproductive changes of adolescence.

Other important hormones include:

• Thyroxine – regulates metabolism

• Insulin – controls blood sugar

• Adrenaline – prepares the body to respond to stress

Reproductive Phase in Humans

Adolescents enter the reproductive phase once their sex organs mature and start producing gametes (sperm in boys and eggs in girls).

• In girls, the reproductive phase begins at puberty and lasts until about 45–50 years. The menstrual cycle involves egg release, thickening of the uterine lining, and shedding if pregnancy does not occur.

• The start of menstruation is called menarche. The end of menstruation is called menopause.

How is the Sex of the Baby Determined?

The sex of a baby depends on the chromosomes carried by the sperm.

• Females have XX chromosomes.

• Males have XY chromosomes.

• If an X-bearing sperm fertilizes the egg → the baby will be female (XX).

• If a Y-bearing sperm fertilizes the egg → the baby will be male (XY).

 

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Important Definitions

1. Adolescence: Transition between childhood and adulthood (11–19 years), marked by physical and emotional changes.

2. Puberty: The stage when the body becomes sexually mature.

3. Larynx: Voice box in the throat that produces sound.

4. Sebaceous Gland: Oil gland in the skin; overactivity causes acne.

5. Acne: Skin condition with pimples due to overactive oil glands.

6. Testicle (Testis): Male organ producing sperm and testosterone.

7. Ovary: Female organ producing eggs and hormones.

8. Pituitary Gland: Master gland controlling hormone release.

9. Testosterone: Male hormone responsible for male traits.

10. Estrogen: Female hormone regulating female traits and menstruation.

11. Menstrual Cycle: Monthly changes in the female reproductive system.

12. Menarche: First menstrual cycle in females.

13. Menopause: End of menstruation and reproductive years in women.

14. Sex Chromosome: Chromosomes that decide the baby’s sex (XX or XY).

15. Thyroxine: Hormone that regulates metabolism.

16. Insulin: Hormone that regulates blood sugar.

17. Adrenaline: Hormone that helps the body respond to stress.

Recap

• Adolescence lasts from 11–19 years.

• Puberty brings growth, body changes, voice changes, and development of sex organs.

• Hormones control these changes.

• Adolescents become capable of reproduction.

• The sex of the baby is determined by the father’s sperm chromosome (X or Y).

Important Questions

1. What is adolescence?

2. Explain puberty and its main changes.

3. Why do boys’ voices crack during puberty?

4. What role do hormones play in adolescence?

5. What is menarche and menopause?

6. How is the sex of the baby determined?

 

Class 8th Science – Reaching the Age of Adolescence Notes by The Busy Brains

 

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