NCERT 8th Class (CBSE) Science: Reaching the Age of Adolescence

Question: Choose the correct option: Adolescents should be careful about what they eat, because

1. proper diet develops their brains.
2. proper diet is needed for the rapid growth taking place in their body.
3. adolescents feel hungry all the time.
4. taste buds are well developed in teenagers.

Answer: Adolescents should be careful about what they eat, because proper diet is needed for the rapid growth taking place in their body.

Question: Choose the correct option: Reproductive age in women starts when their

1. menstruation starts.
2. breasts start developing.
3. body weight increases.
4. height increases.

Answer: Reproductive age in women starts when their menstruation starts.

Question: Choose the correct option: The right meal for adolescents consists of

1. chips, noodles, coke.
2. chapatti, dal, vegetables.
3. rice, noodles and burger.
4. vegetable cutlets, chips and lemon drink.

Answer: The right meal for adolescents consists of chapatti, dal, vegetables.

Question: Write notes on:

1. Adam’s apple.
2. Secondary sexual characters.
3. Sex determination in the unborn baby.

Answer: (a) Adam’s apple: In human males, the larynx grows larger during puberty and can be seen as a protruding part of the throat. This protrusion is known as the Adam’s apple. In boys, under the influence of sex hormones, the larynx becomes prominent. As a result, the vocal cords become longer and thicker, causing the voice to become hoarse.

However, in females, the larynx is of a small size and is hardly visible. Therefore, girls have a high pitched voice, while the voice of boys is low pitched.

(b) Secondary sexual characters are those features that help in distinguishing the male and the female body from each other. They are physical or behavioral characteristics that appear in humans at the time of puberty.

Secondary sexual characters in boys: 

1. Appearance of moustache and beard.
2. Appearance of chest hair.
3. Growth of hair in genital area and other parts of the skin.

Secondary sexual character in girls:

1. Increase in breast size and darkening of the skin of nipples present at the tip of the breasts.
2. Growth of hair in genital area and other body parts.

(c) Sex determination in an unborn baby: Whether the baby will be a boy or a girl is determined by the chromosomes present inside the nucleus of the fertilized egg. There are 23 pairs, i.e. 46 chromosomes, in every normal human cell. In each pair, one chromosome comes from the father and one from the mother.

Two out of these 46 chromosomes are sex chromosomes, called X and Y chromosomes. A female has two X sex-chromosomes and a male has one X and one Y sex chromosomes. Each gamete has only one chromosome. An egg has an X chromosome. A sperm may have an X or a Y chromosome.

1. If a sperm containing an X chromosome fertilizes the egg, the zygote would have two X chromosomes and would develop into a female.
2. If a sperm containing a Y chromosome fertilizes the egg, the zygote would have one X and one Y chromosomes and would develop into a male.

It can be seen from the above that the sex chromosomes of the father, rather than those of the mother, determine the sex of the child.