Class 8 Science Notes Chapter 10 (Chapter 10) – Examplar Problems Book

Alright class, let's focus on Chapter 10, 'Reaching the Age of Adolescence,' from your Science Exemplar book. This is an important chapter, not just for your school exams but also for various government competitive exams, as it deals with fundamental biological changes in humans. Pay close attention to the definitions, processes, and the role of hormones.

Chapter 10: Reaching the Age of Adolescence - Detailed Notes

1. Adolescence and Puberty:

• Adolescence: The period of life when the body undergoes significant changes, leading to reproductive maturity. It typically starts around the age of 11 and lasts up to 18 or 19 years. Adolescents are also called 'teenagers' (covering ages 13 to 19).
• Puberty: The specific period within adolescence during which adolescents reach sexual maturity and become capable of reproduction. It marks the onset of adolescence. The changes occurring during puberty are triggered by hormones.

2. Changes During Puberty:

• a) Increase in Height:
  • Sudden and rapid increase in height due to the elongation of long bones (arms and legs).
  • Rate of growth varies among individuals. Girls generally grow faster than boys initially but reach their maximum height earlier.
  • Maximum height is largely determined by genetics inherited from parents.
• b) Change in Body Shape:
  • Boys: Shoulders broaden, chest becomes wider, muscles grow more prominently.
  • Girls: Region below the waist becomes wider, hips broaden.
• c) Change in Voice:
  • Boys: The voice box or larynx begins to grow larger, often protruding as the 'Adam's apple'. This causes the voice to deepen and become hoarse initially, then stabilize.
  • Girls: Larynx grows but less prominently, so the voice generally remains high-pitched.
• d) Increased Activity of Sweat and Sebaceous Glands:
  • Secretion of sweat (sudoriferous glands) and oil (sebaceous glands) increases significantly.
  • This can lead to acne and pimples on the face due to bacterial action on trapped oil and sweat.
• e) Development of Sex Organs:
  • Boys: Testes and penis develop completely. Testes start producing sperm.
  • Girls: Ovaries enlarge, and eggs begin to mature. Ovaries start releasing mature eggs (ovulation). Uterus develops.
• f) Reaching Mental, Intellectual, and Emotional Maturity:
  • Adolescence is also a time of significant cognitive and emotional development.
  • Increased capacity for learning, abstract thinking, and reasoning.
  • Tendency towards self-consciousness, mood swings, and seeking independence. Peer group influence becomes strong.

3. Secondary Sexual Characters:

• These are features that help distinguish males from females physically but are not directly involved in reproduction.
• Boys: Growth of facial hair (moustache, beard), hair on the chest, underarms, and pubic region; deepening of the voice.
• Girls: Development of breasts, growth of hair underarms and pubic region; onset of menstruation.
• These changes are controlled by sex hormones.

4. Role of Hormones:

• Hormones: Chemical substances secreted by endocrine glands that travel through the bloodstream to target sites/organs, stimulating specific changes.
• Endocrine Glands (Ductless Glands): Glands that release hormones directly into the bloodstream.
• Key Glands and Hormones in Puberty:
  • Pituitary Gland: Often called the 'master gland'. It secretes hormones that stimulate the testes and ovaries to produce their respective hormones. It also produces Growth Hormone.
  • Testes (in Males): Produce the male sex hormone Testosterone. Testosterone triggers male secondary sexual characters and sperm production.
  • Ovaries (in Females): Produce the female sex hormone Estrogen. Estrogen triggers female secondary sexual characters, breast development, and maturation of eggs. Ovaries also produce Progesterone, which primarily helps maintain pregnancy.
• Hormonal Control Mechanism: Pituitary hormones stimulate testes/ovaries -> Testes/Ovaries release Testosterone/Estrogen -> These hormones travel via blood to target sites (e.g., voice box, skin, breasts, bones) -> Stimulate changes associated with puberty. This is regulated by a feedback mechanism.

5. Reproductive Phase of Life in Humans:

• Begins at puberty when gamete (sperm and ova) production starts.
• In Females:
  • Menarche: The first occurrence of menstruation, typically between ages 10-13. Marks the beginning of the reproductive phase.
  • Menstruation: The cyclical shedding of the uterine lining, along with blood and the unfertilised egg, occurring approximately every 28-30 days.
  • Ovulation: Release of a mature egg from the ovary, usually around the middle of the menstrual cycle.
  • Menopause: The cessation (stopping) of menstruation and ovulation, typically occurring between ages 45-55. Marks the end of the reproductive phase in females.
• In Males: The reproductive phase lasts much longer than in females, often throughout life after puberty.

6. Sex Determination in Humans:

• Human cells have 23 pairs of chromosomes (46 total) in the nucleus.
• One pair constitutes the Sex Chromosomes:
  • Females have two X chromosomes (XX). All female eggs carry an X chromosome.
  • Males have one X and one Y chromosome (XY). Sperm can carry either an X or a Y chromosome (50% chance for each).
• Determination of Baby's Sex:
  • If a sperm carrying an X chromosome fertilizes the egg (X), the zygote will be XX (Female).
  • If a sperm carrying a Y chromosome fertilizes the egg (X), the zygote will be XY (Male).
  • Therefore, the father's sperm determines the sex of the child.

7. Hormones Other Than Sex Hormones:

• The endocrine system includes other glands producing vital hormones:
  • Thyroid Gland: Produces Thyroxine. Regulates metabolism. Deficiency causes Goitre.
  • Pancreas: Produces Insulin. Regulates blood sugar levels. Deficiency causes Diabetes.
  • Adrenal Glands: Produce Adrenaline. Helps the body cope with stress ('fight or flight' hormone).
  • Pituitary Gland: Also produces Growth Hormone (GH), essential for normal growth.

8. Role of Hormones in Metamorphosis (Insects and Frogs):

• Metamorphosis: The process of transformation from larva to adult through drastic changes.
• Insects: Insect hormones control metamorphosis (e.g., from caterpillar to pupa to adult butterfly).
• Frogs: Metamorphosis from tadpole to adult frog is controlled by Thyroxine (produced by the thyroid gland).
  • Thyroxine production requires iodine in the water. Tadpoles in iodine-deficient water cannot metamorphose into frogs.

9. Reproductive Health during Adolescence:

• a) Nutritional Needs:
  • Adolescence is a period of rapid growth, requiring a balanced diet.
  • A balanced diet includes proteins, carbohydrates, fats, vitamins, and minerals in adequate proportions (e.g., roti/rice, dal, vegetables, milk, fruits).
  • Iron is crucial for blood formation (especially for girls during menstruation). Iron-rich foods include leafy vegetables, jaggery, meat, amla.
  • Calcium is needed for bone growth (milk, dairy products).
  • Avoid junk food as it lacks nutritional value.
• b) Personal Hygiene:
  • Increased sweat and oil production necessitates regular bathing (at least once a day).
  • Maintaining cleanliness of all body parts is essential to prevent infections.
  • Girls need to take special care of hygiene during menstruation, using clean sanitary napkins and changing them regularly.
• c) Physical Exercise:
  • Regular exercise, walking, playing outdoor games keeps the body fit and healthy.
• d) Say NO to Drugs:
  • Adolescence is a vulnerable age. Peer pressure might lead to experimenting with drugs.
  • Drugs are addictive and harmful, ruining health and happiness. Avoid them completely.
  • HIV/AIDS can spread through sharing syringes used for injecting drugs, besides sexual contact with an infected person.

Multiple Choice Questions (MCQs)

1. The period marking the end of the reproductive phase in a woman's life is called:
   (a) Menarche
   (b) Menstruation
   (c) Menopause
   (d) Puberty

2. Which hormone is primarily responsible for the development of male secondary sexual characters like beard and moustache?
   (a) Estrogen
   (b) Progesterone
   (c) Testosterone
   (d) Adrenaline

3. The voice box in humans is also known as the:
   (a) Pharynx
   (b) Larynx
   (c) Trachea
   (d) Oesophagus

4. Acne and pimples during adolescence are primarily due to the increased activity of:
   (a) Sweat glands only
   (b) Sebaceous glands only
   (c) Both sweat and sebaceous glands
   (d) Pituitary gland

5. In humans, the sex of the baby is determined by:
   (a) The chromosome contributed by the mother
   (b) The chromosome contributed by the father
   (c) The nutritional status of the mother
   (d) The timing of fertilization

6. Which endocrine gland is referred to as the 'master gland'?
   (a) Thyroid gland
   (b) Adrenal gland
   (c) Pancreas
   (d) Pituitary gland

7. The first menstrual flow that begins at puberty is termed:
   (a) Menopause
   (b) Menarche
   (c) Ovulation
   (d) Fertilization

8. Metamorphosis in tadpoles requires the presence of which hormone in the water?
   (a) Insulin
   (b) Adrenaline
   (c) Thyroxine
   (d) Estrogen

9. A human female has which combination of sex chromosomes?
   (a) XY
   (b) XX
   (c) XO
   (d) YY

10. Which of the following is NOT a secondary sexual character in boys?
    (a) Deepening of voice
    (b) Development of breasts
    (c) Growth of facial hair
    (d) Broadening of shoulders

Answer Key for MCQs:

1. (c) Menopause
2. (c) Testosterone
3. (b) Larynx
4. (c) Both sweat and sebaceous glands
5. (b) The chromosome contributed by the father
6. (d) Pituitary gland
7. (b) Menarche
8. (c) Thyroxine (Note: Thyroxine is produced by the tadpole's thyroid gland, but its production requires iodine from the water.)
9. (b) XX
10. (b) Development of breasts (This is a female secondary sexual character)

Make sure you revise these notes thoroughly. Understanding the role of hormones and the changes during adolescence is key. Good luck with your preparation!