CBSE Class 8 Science Exemplar Chapter 10: Reaching the Age of Adolescence NCERT Solutions

Reviewed by NCERT Help Editorial Team · Updated on 29 Jul 2026

NCERT Solutions PDF Class 8 PDF

CBSE Class 8 Science chapter 'Reaching the Age of Adolescence' explores the profound biological and physiological transformations during human puberty. The solutions detail the hormonal mechanisms governing adolescence, differentiate between male and female reproductive systems, and explain the reproductive process from fertilization to embryo development. They also address the prevention of sexually transmitted infections like AIDS. Furthermore, the chapter examines metamorphosis in amphibians, highlighting the crucial role of iodine in this developmental change. These explanations are designed to clarify intricate subjects, serving as a vital aid for students aiming for academic success and a comprehensive understanding of human growth and reproductive health.

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Quick info

Board	CBSE
Class	Class 8
Subject	Science Exemplar
Session	2026
Language	English
Type	NCERT Solutions
Chapter	Chapter 10

Chapter summary

Chapter 10, 'Reaching the Age of Adolescence,' focuses on the biological transformations during puberty. The NCERT Solutions explain the hormonal changes, secondary sexual characteristics in boys and girls, the reproductive process from gamete maturation to embryo implantation, and the transmission and prevention of AIDS. It also touches upon metamorphosis in tadpoles and the essential role of iodine. These solutions aim to clarify the scientific aspects of growing up and reproduction for Class 8 students.

Learning outcomes

Understand the biological changes during adolescence and puberty.
Explain the role of hormones in sexual development.
Describe the process of human reproduction, including fertilization and embryo development.
Identify the modes of transmission and prevention of AIDS.
Explain the process of metamorphosis and the role of iodine in tadpole development.
Differentiate between male and female sex chromosomes and their role in determining the sex of a child.

Topics covered

Paper topics

Adolescence and Puberty
Hormonal Changes
Secondary Sexual Characteristics
Reproductive System
Fertilization and Embryo Development
Sex Determination
AIDS Transmission and Prevention
Metamorphosis
Role of Iodine
Changes in Boys during Puberty

Important topics

Puberty and Hormonal Control
Human Reproduction Process
Sex Determination
AIDS Transmission and Prevention
Metamorphosis

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Questions and Solutions

Multiple Choice Questions

1. The belief that the mother is completely responsible for the sex of the child is wrong because the child

(a) gets sex chromosome only from the mother.

(b) develops in the body of the mother.

(d) gets sex chromosome only from the father.

Solution: The correct option is (c). The sex of a child is determined by the sex chromosomes inherited from both parents. The mother contributes an X chromosome, while the father contributes either an X chromosome (resulting in a female child, XX) or a Y chromosome (resulting in a male child, XY). Therefore, the father's chromosome determines the sex of the child, not solely the mother's.

2. AIDS can spread from an infected person to another person through

(a) sharing food

(b) blood transfusion

(d) a mosquito bite

Solution: The correct option is (b) blood transfusion. AIDS (Acquired Immunodeficiency Syndrome) is caused by the HIV virus and can be transmitted through infected blood, sharing of needles and syringes, sexual contact, and from an infected mother to her child during pregnancy, childbirth, or breastfeeding. It is not transmitted through casual contact like sharing food, combs, or via mosquito bites.

Events leading to pregnancy and development of embryo

3. Given below are events that lead to pregnancy and development of embryo:

i) Fertilization of egg

ii) Maturation of egg

iii) Release of egg

iv) Embedding of embryo in thickened uterine wall.

Which of the following options gives the correct order of sequence in which they occur?

(a) i, ii, iii, iv

(b) ii, i, iii, iv

(d) ii, iii, i, iv

Solution: The correct option is (d) ii, iii, i, iv. The sequence of events is as follows: First, after puberty, the egg matures (ii). Then, the mature egg is released from the ovary (iii). If sperm are present, fertilization occurs, forming a zygote (i). The zygote undergoes cell division to form an embryo, which then embeds itself in the thickened uterine wall for further development (iv).

Metamorphosis of tadpoles

4. For the metamorphosis of tadpoles, which of the following elements must be available in water?

(a) chlorine

(b) carbon

(d) iodine

Solution: The correct option is (d) iodine. Metamorphosis, the transformation of a tadpole into a frog, is regulated by the hormone thyroxine. The thyroid gland produces thyroxine, and iodine is a crucial component required for the synthesis of this hormone. Therefore, iodine must be present in the water for tadpoles to undergo metamorphosis successfully.

Changes during puberty in boys

5. The most conspicuous visible change that occurs in boys during puberty is:

(a) development in voice box.

(b) increase in height.

(d) increased sweating.

Solution: The most conspicuous visible change among the options provided is (a) development in the voice box. During puberty, boys experience a significant growth in their larynx (voice box), leading to a deepening of the voice. While height increase (b), sperm production (c), and increased sweating (d) also occur, the change in voice is often the most noticeable and audible transformation.

Common mistakes

Incorrectly attributing the determination of a child's sex solely to the mother.
Misunderstanding the modes of transmission for diseases like AIDS.
Confusing the sequence of events in human reproduction.
Not recognizing the specific element required for tadpole metamorphosis.

Revision tips

Review the diagrams of the male and female reproductive systems to understand their functions.
Create flashcards for key terms like puberty, hormones, fertilization, and metamorphosis.
Focus on understanding the correct sequence of reproductive events.
Pay close attention to the ways diseases like AIDS are transmitted and prevented.
Memorize the role of specific elements like iodine in biological processes.

Practice MCQs

Q1. The determination of the sex of a child is primarily influenced by:

Q2. Which of the following is NOT a mode of transmission for AIDS?

Q3. What is the correct sequence of events leading to embryo development?

Q4. The metamorphosis of tadpoles into frogs requires the presence of which element in water?

Q5. A significant visible change in boys during puberty is:

Frequently asked questions

What is the main topic of Chapter 10 for Class 8 Science Exemplar?

Chapter 10, 'Reaching the Age of Adolescence,' focuses on the biological changes that occur during puberty, human reproduction, and related concepts like metamorphosis.

How do these NCERT Solutions help students?

These solutions provide clear, step-by-step explanations for each question, helping students understand complex topics like hormonal changes, reproduction, and disease transmission, which is crucial for exam preparation.

Who is responsible for the sex of a child?

The father is responsible for the sex of the child. The child inherits an X chromosome from the mother and either an X or a Y chromosome from the father. A Y chromosome from the father results in a male child.

What is metamorphosis and what element is crucial for it?

Metamorphosis is the process of transformation from an immature form to an adult form in two or more distinct stages, like a tadpole becoming a frog. Iodine is essential for this process as it helps produce the hormone thyroxine.

Can AIDS be spread by sharing food?

No, AIDS cannot be spread by sharing food. It is transmitted through specific means such as sharing needles, blood transfusions, sexual contact, and from mother to child.

What are the key changes during puberty in boys?

Key changes include the deepening of the voice due to voice box development, increased height, growth of facial and body hair, and the production of sperms.

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