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Tamil Nadu (TNBSE)Class 8 Science★ 5-8 marks in the TN Class 8 annual exam through book-back MCQs, fill-ups and short answers

Reaching the Age of Adolescence

Samacheer Kalvi (TN State Board) Class 8 Science — Biology Chapter 20, Reaching the Age of Adolescence. Adolescence and puberty, secondary sexual characters in boys and girls, the endocrine glands and their hormones, sex determination by chromosomes, the menstrual cycle, and the importance of a balanced diet and hygiene. Notes with the actual book-back questions, common mistakes and quick revision.

⏱ 16 min readEasy difficulty✓ Free · NCERT-aligned

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By the end of this chapter you'll be able to…

1Define adolescence and puberty
2List secondary sexual characters in boys and girls
3Match endocrine glands to their hormones
4Explain sex determination by chromosomes
5Describe the menstrual cycle and adolescent health

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Why this chapter matters

Reaching the Age of Adolescence explains the changes of puberty, the hormones and glands behind them, how sex is determined and how to stay healthy as a teenager. The master gland, Adam's apple and sex determination by the father are directly tested book-back content in the TN Class 8 exam.

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Chapter 18 — Organisation of Life

Body systems.

Reaching the Age of Adolescence — Class 8 Science (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 8 Science, Biology — Chapter 20. Growing up — the changes of puberty and the glands behind them.

1. About this chapter

This chapter covers adolescence and puberty, secondary sexual characters, the endocrine glands and hormones, sex determination, the menstrual cycle, and health during adolescence.

2. Adolescence and puberty

Adolescence is the period of life from about 11 to 19 years.
The age at which a person becomes capable of reproduction (sexual maturity) is called puberty.

3. Secondary sexual characters

These are the physical features that distinguish males from females and appear at puberty:

In boys: facial and body hair, broader shoulders, and a deeper voice — the larynx grows to form the Adam's apple.
In girls: breasts develop, hips become wider, and menstruation begins (the first flow is called menarche).

4. Endocrine glands and hormones

Hormones are chemical substances secreted by endocrine (ductless) glands directly into the blood.

Gland	Hormone	Role
Pituitary	growth hormone	"master gland"; controls other glands
Thyroid	thyroxine	needs iodine; deficiency causes goitre
Pancreas	insulin	controls blood sugar (diabetes if low)
Testes	testosterone	male characters
Ovaries	oestrogen	female characters

5. Sex determination and the menstrual cycle

Sex is decided by chromosomes: a female is XX, a male is XY. The father's sperm (X or Y) determines the sex of the child.
The menstrual cycle is about 28 days; menarche is the first menstruation and menopause is when it stops (around 45–50 years). Cleanliness during menstruation is important to avoid infection.

6. Worked examples

Example 1. What is the Adam's apple? The growth of the larynx in boys at puberty.

Example 2. Which gland is the master gland? The pituitary gland.

Example 3. Whose chromosome determines the sex of a child? The father's (the sperm carries X or Y).

7. Book-back questions (Samacheer Kalvi)

I. Choose the correct answer

The period of life between 11 and 19 years is called — (a) adolescence / (b) infancy. Ans: (a) adolescence.
The "master gland" of the body is the — (a) thyroid / (b) pituitary. Ans: (b) pituitary.
The Adam's apple is the growth of the — (a) larynx / (b) lungs. Ans: (a) larynx.
The hormone secreted by the thyroid gland is — (a) insulin / (b) thyroxine. Ans: (b) thyroxine.
The sex of a child is determined by the — (a) mother / (b) father. Ans: (b) father.

II. Fill in the blanks 6. Chemical substances secreted by endocrine glands are called hormones. 7. The first menstrual flow is called menarche. 8. A male has the sex chromosomes XY.

III. Answer briefly 9. Name two secondary sexual characters in boys. 10. Why is iodine important in the diet?

8. Common mistakes

Mistake: Saying the mother determines the child's sex. Fix: The father's sperm (X or Y) decides the sex.
Mistake: Calling the thyroid the master gland. Fix: The pituitary is the master gland; the thyroid secretes thyroxine.
Mistake: Confusing menarche and menopause. Fix: Menarche = first menstruation; menopause = when it stops.

9. Quick revision

Biology Ch 20 · adolescence, hormones, reproduction.
Adolescence ≈ 11–19 years; puberty = sexual maturity.
Secondary characters: boys (facial hair, Adam's apple), girls (breasts, menarche).
Endocrine glands: pituitary (master), thyroid (thyroxine, iodine → goitre), pancreas (insulin), testes/ovaries.
Sex: XX female, XY male; father's sperm decides.
Menstrual cycle ≈ 28 days; menarche (first) and menopause (stops). Hygiene matters.

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

Adolescence / puberty

adolescence ≈ 11–19 yrs; puberty = sexual maturity

Growing up.

Endocrine glands

pituitary (master), thyroid (thyroxine), pancreas (insulin)

Hormones into blood.

Sex determination

XX female, XY male; father's sperm decides

Chromosomes.

Menstrual cycle

≈ 28 days; menarche (first), menopause (stops)

Hygiene matters.

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Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT

✗ Saying the mother determines the child's sex

✓ The father's sperm (X or Y) decides the sex.

WATCH OUT

✗ Calling the thyroid the master gland

✓ The pituitary is the master gland; the thyroid secretes thyroxine.

WATCH OUT

✗ Confusing menarche and menopause

✓ Menarche = first menstruation; menopause = when it stops.

NCERT exercises (with solutions)

Every NCERT exercise from this chapter — what it covers and how many questions to expect.

Choose the correct answer

Book-back MCQs on adolescence, master gland, Adam's apple and sex determination.

Questions

Fill in the blanks

Hormones, menarche and sex chromosomes.

Questions

Answer briefly

Secondary characters, iodine, menstrual hygiene.

Questions

Practice problems

Try each one yourself before tapping "Show solution". Active recall > rereading.

Q1EASY· MCQ

The 'master gland' of the body is the ____.

▶ Show solution

pituitary gland.

Q2EASY· MCQ

The Adam's apple is the growth of the ____.

▶ Show solution

larynx.

Q3EASY· MCQ

The sex of a child is determined by the ____.

▶ Show solution

father.

Q4EASY· Fill in the blanks

The first menstrual flow is called ____.

▶ Show solution

menarche.

Q5EASY· Answer briefly

Why is iodine important in the diet?

▶ Show solution

Iodine is needed by the thyroid gland to make thyroxine; its deficiency causes goitre (swelling of the thyroid).

Q6MEDIUM· Answer briefly

How is the sex of a child determined?

▶ Show solution

A female has XX and a male has XY chromosomes. The mother always gives an X; the father's sperm gives either X (girl) or Y (boy), so the father determines the child's sex.

5-minute revision

The whole chapter, distilled. Read this the night before the exam.

•Biology Chapter 20 of Samacheer Kalvi Class 8 Science.
•Adolescence ≈ 11–19 years; puberty = sexual maturity.
•Secondary characters: boys (facial hair, Adam's apple = larynx), girls (breasts, menarche).
•Endocrine glands: pituitary (master), thyroid (thyroxine, iodine → goitre), pancreas (insulin).
•Sex: XX female, XY male; the father's sperm decides.
•Menstrual cycle ≈ 28 days; menarche (first), menopause (stops); hygiene is important.

Tamil Nadu (TNBSE) marks blueprint

Where the marks come from in this chapter — so you can plan your prep.

Typical chapter weightage: 5-8 marks across book-back MCQ, fill-ups and short answers

Question type	Marks each	Typical count	What it tests
MCQ / Fill	1	3-5	Glands, hormones, sex chromosomes
Short Answer	2-3	1-2	Secondary characters, sex determination
Application	2	1	Diet and hygiene

Prep strategy

Match each gland to its hormone
Remember the pituitary is the master gland
Learn that the father determines sex (XX/XY)
Note iodine for thyroxine and menstrual hygiene

Where this shows up in the real world

This chapter isn't just an exam topic — it lives in the world around you.

Health

Understanding hormones explains growth, diabetes and thyroid disorders.

Hygiene

Knowing menstrual care helps prevent infections.

Nutrition

Iodised salt prevents goitre in the community.

Exam strategy

Battle-tested tips from teachers and toppers for this chapter.

Match glands to hormones in a table
State the pituitary is the master gland
Explain sex determination (father, XX/XY)
Link iodine to thyroxine and goitre

Going beyond the textbook

For olympiad aspirants and curious learners — topics that build on this chapter.

Explain how a hormone imbalance can affect growth.
Trace what happens in the body across one menstrual cycle.

Where else this chapter is tested

CBSE board isn't the only one — other exams test this chapter too.

TN Class 8 Annual ExamHigh

Foundation / NMMS ScienceMedium

School unit testsHigh

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Questions students ask

The real ones — pulled from the Q&A community and tutor sessions.

It secretes hormones that control several other endocrine glands (like the thyroid and the sex glands), so it directs much of the body's hormone system.

The body grows rapidly at this age, so it needs extra proteins, vitamins, iron and calcium to support that growth and to keep the blood and bones healthy.

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