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Science: Class 8 — Chapter 7: Reaching the Age of Adolescence

7.1 Adolescence and Puberty
7.1.1 Introduction to Adolescence
  • Reproductive Capability: Humans and many animals can reproduce only after 'growing up' to a certain age.
  • Body Changes: This chapter covers changes in the human body that lead to reproductive capability.
  • Role of Hormones: Discusses how hormones cause changes that turn a child into an adult.
7.1.2 Defining Adolescence
  • Growth Spurt: A sudden noticeable increase in growth occurs around age 10 or 11.
  • Adolescence: The period of life when the body undergoes changes leading to reproductive maturity.
  • Age Range: Typically begins around 11 and lasts up to 18 or 19 years of age.
  • Teenagers: Adolescents are also called 'teenagers' as this period covers the 'teens' (13 to 18 or 19 years).
  • Gender Variation: In girls, adolescence may begin a year or two earlier than in boys.
7.1.3 Understanding Puberty
  • Onset of Puberty: Changes during adolescence mark the beginning of puberty.
  • Key Change: The most significant change is that boys and girls become capable of reproduction.
  • End of Puberty: Puberty concludes when an adolescent achieves reproductive maturity.
7.2 Changes at Puberty
7.2.1 Increase in Height
  • Conspicuous Change: The most obvious change during puberty is a sudden increase in height.
  • Bone Elongation: Long bones of the arms and legs elongate, contributing to increased height.
  • Growth Rate: Initially, girls grow faster than boys, but both typically reach maximum height by around 18 years.
  • Individual Variation: The rate of height growth varies among individuals; some grow suddenly, others gradually.
  • Body Proportion: All body parts do not grow at the same rate, leading to temporary disproportions that eventually balance out.
  • Genetic Influence: Height is largely determined by genes inherited from parents.
  • Nutritional Needs: Proper nutrition during these years is crucial for the adequate growth of bones, muscles, and other body parts.
7.2.2 Change in Body Shape
  • Boys: Shoulders generally broaden, and chests become wider due to growth. Muscles of the body grow more prominently.
  • Girls: The region below the waist becomes wider.
  • Gender Differences: Changes occurring in adolescent boys and girls are distinct.
7.2.3 Voice Change
  • Larynx Growth: At puberty, the voice box (larynx) begins to grow, becoming larger in boys.
  • Adam's Apple: In boys, the growing voice box can be seen as a protruding part of the throat called Adam’s apple.
  • Girls' Larynx: In girls, the larynx is smaller and hardly visible from the outside.
  • Voice Pitch: Girls generally have a high-pitched voice, while boys develop a deep voice.
  • Hoarse Voice: Sometimes, in adolescent boys, the muscles of the growing voice box go out of control, causing a temporary hoarseness for a few days or weeks.
7.2.4 Increased Activity of Sweat and Sebaceous Glands
  • Gland Secretion: During puberty, the secretion of sweat glands and sebaceous glands (oil glands) increases.
  • Acne and Pimples: Increased activity of these skin glands often leads to acne and pimples in young people.
  • Gland Types: Sweat, oil, and salivary glands release secretions through ducts. Endocrine glands release hormones directly into the bloodstream (ductless glands).
7.2.5 Development of Sex Organs
  • Male Sex Organs: Testes and penis develop completely, and testes begin to produce sperms.
  • Female Sex Organs: Ovaries enlarge, eggs begin to mature, and ovaries start releasing mature eggs.
7.2.6 Reaching Mental, Intellectual and Emotional Maturity
  • Way of Thinking: Adolescence involves a change in a person's way of thinking.
  • Independence and Self-Consciousness: Adolescents become more independent and self-conscious.
  • Intellectual Development: The brain has a great capacity for learning during this period, and individuals spend considerable time thinking.
  • Insecurity: Adolescents may sometimes feel insecure while adjusting to body and mind changes, but these are natural parts of growing up.
7.3 Secondary Sexual Characters
7.4 Role of Hormones in Initiating Reproductive Function
7.5 Reproductive Phase of Life in Humans
7.5.1 Onset of Reproductive Capability
  • Gamete Production: Adolescents become capable of reproduction when testes and ovaries begin producing gametes.
  • Duration of Fertility: The capacity for maturation and production of gametes lasts much longer in males than in females.
7.5.2 Female Reproductive Phase: Menstrual Cycle
  • Beginning: Reproductive phase in females starts at puberty (10-12 years) and typically lasts until 45-50 years.
  • Ovum Maturation: Ova begin to mature with puberty. One ovum matures and is released by an ovary approximately every 28-30 days.
  • Uterine Preparation: The uterus wall thickens to receive a fertilised egg; this prepares for potential pregnancy.
  • Menstruation: If fertilisation does not occur, the released egg and thickened uterine lining (with blood vessels) are shed, causing bleeding.
  • Frequency: Menstruation occurs once every 28-30 days.
  • Menarche: The first menstrual flow, which begins at puberty, is called menarche.
  • Menopause: The cessation of the menstrual cycle, occurring around 45-50 years of age, is termed menopause.
  • Irregularity: Initially, the menstrual cycle may be irregular and takes time to become regular.
  • Hormonal Control: The menstrual cycle (egg maturation, release, uterine wall thickening/breakdown) is controlled by hormones.
  • Fertilisation: If the egg is fertilised, it divides and embeds in the uterus for development.
7.6 How is the Sex of the Baby Determined?
7.7 Hormones other than Sex Hormones
7.8 Role of Hormones in Completing the Life History of Insects and Frogs
7.9 Reproductive Health
7.9.1 Importance of Health
  • Well-being: Physical and mental well-being is considered an individual's health.
  • Key Factors: A healthy body requires a balanced diet, personal hygiene, and adequate physical exercise.
  • Adolescent Needs: These factors are even more critical during adolescence due to rapid body growth.
7.9.2 Nutritional Needs of Adolescents
  • Rapid Growth: Adolescence is a stage of rapid growth and development, necessitating a carefully planned diet.
  • Balanced Diet: Meals must include proteins, carbohydrates, fats, and vitamins in requisite proportions.
  • Indian Meal: Roti/rice, dal, and vegetables form a balanced Indian meal.
  • Milk and Fruits: Milk is a balanced food, and fruits provide nourishment.
  • Infant Nutrition: Mother's milk provides all necessary nourishment for infants.
  • Iron-Rich Foods: Iron builds blood; leafy vegetables, jaggery, meat, citrus, and Indian gooseberry (amla) are good for adolescents.
  • Avoid Junk Food: Chips, packed/tinned snacks, though tasty, lack adequate nutritional value and should not replace regular meals.
7.9.3 Personal Hygiene
  • Daily Bath: Everyone should bath at least once daily; teenagers especially need this due to increased sweat gland activity causing body odor.
  • Body Cleanliness: All body parts should be washed and cleaned daily to prevent bacterial infections.
  • Menstrual Hygiene: Girls must take special care during menstrual flow, tracking their cycle and using sanitary pads or clean homemade pads, changing them every 4-5 hours.
7.9.4 Physical Exercise
  • Benefits: Walking and playing in fresh air keep the body fit and healthy.
  • Recommendation: All young boys and girls should take walks, exercise, and play outdoor games.
7.9.5 Myths, Taboos, Do’s and Don’ts
  • Dispelling Myths: Adolescents should discard wrong notions based on scientific facts about human reproduction.
  • Common Myths: Examples include a girl becoming pregnant by looking at boys during menstruation, the mother being responsible for a child's sex, or a girl not being allowed in the kitchen during menstruation.
7.9.6 Say “NO” to Drugs
  • Normal Growth: Adolescence involves much activity in body and mind; do not feel confused or insecure.
  • Drug Danger: Avoid drugs unless prescribed by a doctor; they are addictive, harm the body long-term, and ruin health and happiness.
  • HIV/AIDS: Caused by HIV virus. Can transmit through sharing syringes for drugs, from infected mother to infant via milk, or through sexual contact with an infected person.
7.9.7 Adolescent Pregnancy
  • Legal Age for Marriage: In India, 18 years for girls and 21 years for boys.
  • Risks of Early Motherhood: Teenage mothers are not mentally or physically prepared, leading to health problems for both mother and child.
  • Socio-Economic Impact: Early marriage and motherhood curtail employment opportunities for young women and can cause mental agony due to unpreparedness for responsibilities.