Quick Revision Notes: Class 8 Science

Chapter: Reaching the Age of Adolescence

Adolescence: The period of life, when the body undergoes changes, leading to reproductive maturity. It generally lasts from age 11 to 18 or 19 years.
Puberty: The onset of adolescence during which boys and girls become capable of reproduction.
Key Change: The most important change which marks puberty is that boys and girls become capable of reproduction.

During puberty, the body experiences several distinct physical and physiological transformations:

Increase in Height:
- Sudden growth in height occurs due to the rapid lengthening of long bones (arms and legs) during this phase.
- Calculation of Full Height (Formula): Present Height (cm) / % of full height at this age (from standard chart) × 100
Change in Body Shape:
- Boys: Shoulders grow broader and muscles grow more prominently.
- Girls: Region below the waist becomes wider (hips widen).
Voice Change:
- The voice box or larynx begins to grow.
- In boys, a growing voice box can be seen as a protruding part of the throat called the Adam's apple. Boys develop a deep voice.
- In girls, the voice box is usually small, resulting in a high-pitched voice.
Increased Activity of Sweat and Sebaceous Glands:
- Secretion of sweat and sebaceous (oil) glands increases, often leading to acne and pimples on the face.
Development of Sex Organs:
- Male: Testes and penis develop completely; testes begin to produce sperms.
- Female: Ovaries enlarge; eggs (ova) begin to mature.
Reached Mental, Intellectual, and Emotional Maturity:
- Adolescents become more independent and self-conscious. Brain capacity for learning is at its peak.

Features that help distinguish male from female are called secondary sexual characters.
In Boys: Growth of facial hair (mustache and beard), hair on chest, arms, and legs.
In Girls: Development of breasts, growth of hair in armpits and pubic region.
These features are controlled by hormones.

Hormones: Chemical substances secreted by endocrine glands (ductless glands) directly into the bloodstream to target specific body parts.
Master Gland: The Pituitary gland secretes many hormones, including ones that stimulate testes and ovaries to produce their respective hormones.

Gland	Hormone Secreted	Function / Role
Testes	Testosterone	Controls development of male secondary sexual characters and sperm production.
Ovaries	Estrogen	Controls development of female secondary sexual characters and egg maturation.
Pituitary	Thyroid Stimulating / Growth Hormone, etc.	Stimulates other glands (testes/ovaries) and controls overall body growth.
Adrenal	Adrenaline	Helps the body adjust to stress, anger, or worry (Fight or Flight hormone).

In Females:
- Puberty starts around 10–12 years and lasts till about 45–50 years.
- Menstruation: The shedding of the uterine lining along with blood vessels once every 28 to 30 days if fertilization does not occur.
- Menarche: The first menstrual flow at puberty.
- Menopause: The stoppage of menstruation (around 45 to 50 years of age).
In Males:
- Males can produce sperms from puberty through much of their later life.

Every human cell has 23 pairs of chromosomes (46 chromosomes in total) in its nucleus.
Out of these, 1 pair (2 chromosomes) determines the sex of the individual:
- Females: Possess two X chromosomes (XX).
- Males: Possess one X and one Y chromosome (XY).

All gametes (eggs/ova) produced by females carry an X chromosome.
Sperms are of two types: 50% carry an X chromosome and 50% carry a Y chromosome.
- If a sperm carrying X fertilizes the egg (XX) $\rightarrow$ Baby Girl
- If a sperm carrying Y fertilizes the egg (XY) $\rightarrow$ Baby Boy
Note: The sex of the child is entirely determined by the father's chromosome (Sperm).

Nutritional Needs (Balanced Diet): Adolescence is a stage of rapid growth; hence, the diet must include proteins, carbohydrates, fats, vitamins, and minerals in adequate amounts (e.g., milk, fruits, grains, pulses, green leafy vegetables).
- Iron Deficiency (Anemia): Common in adolescents; needs to be prevented through iron-rich foods like jaggery, meat, citrus fruits, and leafy veggies.
Personal Hygiene:
- Daily bathing is essential due to increased sweat gland activity.
- Girls must maintain special cleanliness during the menstrual cycle.
Say NO to Drugs: Adolescence brings peer pressure and curiosity, but drugs are addictive and ruin physical and mental health.