DAV Class 8 Science Chapter 15 Question Answers – Reaching the Age of Adolescence
Somewhere between childhood and adulthood, the body goes through a big set of changes. Your height shoots up, your voice changes, your skin behaves differently, and your feelings can swing more than before. None of this is random. Chapter 15 of the DAV Class 8 Science book explains what adolescence is, which chemical messengers (hormones) drive these changes, and how to look after your body during this time. This post gives easy answers to every question in the chapter, with a short reason behind each one.
The chapter in one minute
Adolescence is the stage of life when a child grows into an adult. Its first phase, when the body begins changing rapidly towards reproductive maturity, is called puberty. The changes are controlled by hormones, which are chemicals made by glands called endocrine glands. These glands have no ducts (tubes) of their own, so they pour their hormones straight into the blood.
Here are the main glands and what they do:
| Gland | Hormone | What it does |
|---|---|---|
| Pituitary | Several hormones | Controls other glands, including the testes and ovaries |
| Thyroid | Thyroxine | Controls growth and metabolism, and metamorphosis in frogs |
| Adrenal | Adrenaline | Helps the body respond to stress and danger |
| Testes | Testosterone | Brings about male changes at puberty |
| Ovaries | Oestrogen and progesterone | Bring about female changes and control the menstrual cycle |
A. Fill in the blanks
1. Endocrine glands release hormones into the bloodstream.
2. The larynx is also known as the voice box.
3. Acne and pimples are common in adolescence because the sebaceous glands produce more sebum.
4. A shortage of vitamin D reduces the absorption of calcium by the body.
5. Thyroxine is the hormone needed for metamorphosis in a frog.
6. Autosomes are the chromosomes other than the sex chromosomes.
B. Match the following
The textbook gives the answer key as (1) E, (2) D, (3) A, (4) B, (5) C. Since the two columns are shown as a picture in the book, match them with your own copy. These facts will help you make each pair:
The thyroid gland makes thyroxine. The adrenal glands make adrenaline, which handles stress. The testes make testosterone, and the ovaries make oestrogen. The pituitary gland is called the master gland because it controls other glands. A shortage of iodine causes goitre, and a shortage of vitamin D weakens the bones.
C. Choose the correct option
1. The period of rapid change leading to sexual maturity is called puberty.
2. The start of menstruation in a girl is called menarche.
3. The hormone that controls the body’s response to stress is adrenaline.
4. The one that does not make hormones is the sebaceous gland. It makes sebum, an oily substance for the skin, and has ducts, so it is not an endocrine gland.
5. The mineral needed for a tadpole to grow into a frog is iodine. The thyroid needs iodine to make thyroxine.
D. Short answer questions
1. What is adolescence?
Adolescence is the stage of transition from childhood to adulthood. It generally covers the teenage years, from about 11 to 19.
2. Define puberty. What factors influence it?
Puberty is the first phase of adolescence, when the body goes through sudden and noticeable changes. It is influenced by a person’s diet, genes and surroundings.
3. Why are endocrine glands called ductless glands?
Because they have no ducts of their own. They release their hormones directly into the blood, which carries them around the body.
4. Why do tadpoles in iodine-deficient water fail to become frogs?
The thyroid gland needs iodine to make thyroxine. Without enough iodine, there is not enough thyroxine, and without thyroxine the tadpole cannot go through metamorphosis.
5. How does the pituitary gland control the maturation of the gonads?
The pituitary gland in the brain releases hormones that tell the testes and ovaries to start working. In response, the testes make testosterone and the ovaries make oestrogen and progesterone, and these hormones help the gonads to mature.
6. Why are women above fifty generally unable to have children?
Around the age of 45 to 50, a woman’s menstrual cycle stops. This is called menopause, and it marks the end of the reproductive phase of her life.
E. Long answer questions
1. List the changes that take place in males and females during puberty.
- Height and weight: There is a sudden growth spurt. In girls it is most noticeable between about 11 and 13 years, and in boys between about 13 and 15 years.
- Heart and lungs: They grow larger and work more efficiently. These changes are less visible but just as important.
- Body shape: The body takes on a more adult shape, and the changes differ in boys and girls.
- Voice: The larynx grows, and the voice becomes deeper, especially in boys.
- Skin and glands: The sweat glands become more active, and the sebaceous glands make more sebum, which is why acne and pimples are common.
- Reproductive organs: They mature, and the body starts making sperm in boys and eggs in girls.
2. Case study: Arunima and Arun
The passage for this question is given as a picture in the book, so match these answers with it.
(a) Arunima is suffering from goitre, a swelling in the neck. It is caused by a lack of iodine in the diet, which makes the thyroid gland swell.
(b) Arun’s Adam’s apple is growing. This is a normal change in boys at puberty, caused by the growth of the larynx, so he does not need any medicine.
3. How is the sex of an unborn child decided in human beings?
Human body cells have 46 chromosomes. Of these, 44 are autosomes, and the last pair are the sex chromosomes. Females have two X chromosomes (XX), and males have one X and one Y (XY). Every egg carries 22 autosomes and an X chromosome. A sperm carries 22 autosomes plus either an X or a Y.
If an egg is fertilised by a sperm carrying X, the baby will be a girl (XX). If it is fertilised by a sperm carrying Y, the baby will be a boy (XY). So it is the father’s sperm that decides the sex of the child, not the mother.
4. List the events that take place regularly in the female reproductive system from puberty until menopause.
The textbook shows this as a diagram, so use it along with the points below. The events repeat about every 28 days:
- An egg matures in one of the ovaries and is released into the oviduct. This is ovulation, and it happens around the middle of the cycle.
- Meanwhile, the lining of the uterus becomes thick and rich in blood, ready to receive a fertilised egg.
- If the egg is fertilised, it settles in the uterus wall and the baby starts to develop. The cycle pauses during pregnancy.
- If the egg is not fertilised, the thick lining breaks down and leaves the body through the vagina as blood. This is menstruation, and it usually lasts a few days.
- The cycle then begins again. It starts at menarche, during puberty, and stops at menopause, around the age of 45 to 50.
5. Explain the importance of exercise and good personal hygiene in adolescence.
Exercise: Regular activity such as walking, running and playing games helps the body grow and stay fit. It improves digestion and blood flow, makes the lungs work better, and helps beat the stress that comes with adolescence.
Personal hygiene: Because the sweat and sebaceous glands become more active, adolescents need to keep themselves clean. This means bathing daily with soap, brushing the teeth, taking care of the eyes and ears, and keeping the body and clothes neat. Good hygiene prevents skin problems and infections and builds confidence.
Mistakes to avoid in the exam
Students often use adolescence and puberty as if they mean the same thing. Adolescence is the whole stage between childhood and adulthood, and puberty is its first phase.
Another common slip is mixing up menarche and menopause. Menarche is the first period, and menopause is when periods stop for good.
Do not call sebaceous glands endocrine glands. They have ducts and release sebum on the skin, not hormones into the blood.
In the sex determination question, state clearly that the father decides the sex of the child, and show the chromosomes (22 + X or 22 + Y) in your answer.
Frequently asked questions
What is the role of hormones in adolescence?
Hormones act as chemical messengers. They trigger and control growth and the changes of puberty, such as voice change, body growth and the working of the reproductive organs.
Why is the pituitary called the master gland?
Because it releases hormones that control the working of many other glands in the body.
What causes goitre?
A lack of iodine in the diet. The thyroid gland swells, and the neck looks puffy. Using iodised salt helps prevent it.
Why is a balanced diet important during adolescence?
The body is growing fast and needs extra nutrients, including proteins, calcium, iron and vitamins, to grow healthy and strong.
Written for students following the DAV Science book for Class 8. Please cross-check answers with your own textbook and teacher.