NCERT Solutions Science for Class 8 Chapter 10 REACHING THE AGE OF ADOLESCENCE | Class8 Science Chapter 10
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NCERT Solutions Science for Class 8 Chapter 10 REACHING THE AGE OF ADOLESCENCE
class8 science Chapter 10
NCERT Solutions Science for Class 8 Chapter 10 REACHING THE AGE OF ADOLESCENCE
science for class 8 Chapter 10 question answer
1. What is the term used for chemical secretions of endocrine glands responsible for changes taking place in the body?
Answer : Hormones are chemical substances. These are secretions from endocrine glands, or endocrine system.
2. Define adolescence.
Answer : Humans become capable of reproduction after puberty sets in. Children between the ages of 11 and 19 years are called adolescents.
3. What is menstruation? Explain.
Answer : The uterine wall in females prepares itself to receive the developing fertilised egg. In case there is no fertilisation, the thickened lining of the uterine wall breaks down and goes out of the body along with blood. This is called menstruation.
Girls should take special care of cleanliness during the time of menstrual flow. They should keep track of their menstrual cycle and be prepared for the onset of menstruation. Use sanitary napkin or clean homemade pads. Change pads after every 4–5 hours as per the requirement.
4. List changes in the body that take place at puberty.
Answer : Following are the physical changes that occur during puberty
| 1. | Increase in height | |
| 2. | Change in body shape | |
| 3. | Change in voice | |
| 4. | Development of reproductive organs | |
| 5. | Mental development | |
| 6. | Intellectual development | |
| 7. | development of emotional maturity | |
| 8. | development in activity of sweat and oil glands | |
| 9. | Hair grow at various places on the body |
5. Prepare a Table having two columns depicting names of endocrine glands and hormones secreted by them.
Answer : The names of the endocrine glands and the hormones secreted by them are as follows:
| Endocrine glands | Secreted hormones |
| testis | testosterone hormone (male hormone) |
| ovary | estrogen hormone (female hormone) |
| pituitary | growth hormone |
| thyroid | thyroxine |
| parathyroid | parathyroid hormone |
| adrenal | adrenaline hormone |
| pancreas | insulin |
6. What are sex hormones? Why are they named so? State their function.
Answer :
Sex Hormones :- The hormones which are responsible for secondary sexual characteristics are called sex hormones. These are controlled by hormones secreted by the pituitary gland.
They were named so because they are different in male and female sex and As these features help to distinguish the male from the female they are called secondary sexual characters..
There are two types of sex hormones –
(a) male sex hormones (testosterone) and
(b) female hormones (estrogen).
Functions of Male Sex Hormones – Male hormones increase the facial hair of the boy. The ability to produce sperm is produced by this hormone.
Functions of Female Sex Hormone – Through this hormone, secondary sex characteristics in female like growth of breasts, thinning of voice and control of pregnancy etc.
7. Choose the correct option.
| (a) | Adolescents should be careful about what they eat, because | ||
| (i) | proper diet develops their brains. | ||
| (ii) | proper diet is needed for the rapid growth taking place in their body. | ||
| (iii) | adolescents feel hungry all the time. | ||
| (iv) | taste buds are well developed in teenagers. | ||
Answer : (ii) proper diet is needed for the rapid growth taking place in their body.
| (b) | Reproductive age in women starts when their | ||
| (i) | menstruation starts. | ||
| (ii) | breasts start developing. | ||
| (iii) | body weight increases. | ||
| (iv) | height increases. | ||
Answer : (i) menstruation starts.
| (c) | The right meal for adolescents consists of | ||
| (i) | chips, noodles, coke. | ||
| (ii) | chapati, dal, vegetables. | ||
| (iii) | rice, noodles and burger. | ||
| (iv) | vegetable cutlets, chips and lemon drink. | ||
Answer : (iv) vegetable cutlets, chips and lemon drink.
8. Write notes on —
| (a) | Adam’s apple. | |
| (b) | Secondary sexual characters. | |
| (c) | Sex determination in the unborn baby. |
Answer :
(a) Adam’s apple
At puberty, the voice box or the larynx begins to grow. Boys develop larger voice boxes. The growing voice box in boys can be seen as a protruding part of the throat called Adam’s apple. In girls, the larynx is hardly visible from the outside because of its small size. Generally, girls have a high pitched voice, whereas boys have a deep voice.
(b) Secondary sexual characters
In girls, breasts begin to develop at puberty and boys begin to grow facial hair, that is, moustaches and beard. As these features help to distinguish the male from the female they are called secondary sexual characters. Boys also develop hair on their chest. In both, boys and girls, hair grows under the arms and in the region above the thighs or the pubic region.
(c) Sex determination in the unborn baby
All human beings have 23 pairs of chromosomes in the nuclei of their cells. Two chromosomes out of these are the sex chromosomes, named X and Y. A female has two X chromosomes, while a male has one X and one Y chromosome. The gametes (egg and sperm) have only one set of chromosomes. The unfertilised egg always has one X chromosome. But sperms are of two kinds. One kind has an X chromosome, and the other kind has a Y chromosome.
When a sperm containing X chromosome fertilises the egg, the zygote would have two X chromosomes and develop into a female child. If the sperm contributes a Y chromosome to the egg (ovum) at fertilisation, the zygote would develop into a male child.
