Class 8 | Science | Ch 10 |
Reaching the Age of Adolescence | NCERT Solutions
1. What is the term used for chemical secretions of endocrine glands for changes taking place in the body?
Answer:
Hormones are chemical substances secreted by endocrine glands. They are the chemical substances which co-ordinate the activities of living organism and their growth.
2. Define adolescence.
Answer:
The transition period of physical and mental development which occur between childhood and adulthood is called adolescence.
or
The period of life of a person when the body undergoes a lot of changes leading to reproductive maturity is called Adolescence.
3. What is menstruation? Explain.
Answer:
With the onset of puberty , the eggs begin to mature in the ovaries of a women. One mature egg or ovum is released by one of the ovaries once in about 28 to 30 days. During this period, the inner lining of uterus grows and become thick and spongy, and prepares itself to receive the fertilised egg.In case the fertilisation of egg cell occurs by sperm , the fertilised egg cell begins to divide to form an embryo. The embryo then gets embedded in the thick uterus lining. This results in pregnancy which ultimately leads to the birth of a baby.
If fertilisation does not occur due to lack of sperm , then the egg released by the ovary dies within a few days and the thick lining breaks down. Since the thick uterus lining contains a lot of blood vessels, therefore , the breaking down of uterus lining produces blood along with other tissues. The blood and other tissues come out of vagina of woman in the form of a bleeding. The bleeding from the uterus which occur in a woman or mature girl every month (if the egg cell has not been fertilised) is called menstrual flow or menstruation.
Menstruation occurs every 28 to 30 days because ovulation occurs after every 28 to 30 days .It is also called as monthly periods or menses or periods. It usually lasts for 3 to 5 days in a month.
4. List changes in the body that take place at puberty.
Answer:
Changes which take place at puberty are:
(1) Increase in height
There is sudden increase in the height of boys and girls. The long bones elongate or lengthen and make a person tall. Initially girls grow faster then boys but by about 18 yrs of age, both boys and girls reach maximum height. The maximum height of boys is slightly more than that of girls. Some boys and girls may grow suddenly at puberty and then slow down, while others may grow gradually.
(2) Change in Body shape and appearance
When puberty is set in, a time of rapid changes in body shape and appearance starts in boys and girls which make the boys and girls look different from one another. Testes in the boys and ovaries in girls make different hormones which make the bodies of boys and girls to develop in different way.
(1)Boys develop broader shoulders and wider chests than girls.
(2) Girls develop broader hips than boys. Due to this, the region below waist become wider in girls than boys.
(3) Boys develop more muscle than girls. So, the body of boys look more muscular than that of girls.
(4) Boys develop Adam’s apple which makes them look different from girls.
(5) Girls develop breasts. This also changes the body shape of grown up girls.
(6) Boys develop facial hairs but the girls do not have facial hair.
(3) Change in voice
At puberty, the voice box begins to grow in boys as well as girls. The growth of voice box in boys become much more than the growth of voice box in girls. Due to this, the voice box in boys become much bigger than the voice box in girls.
5. Prepare a Table having two columns depicting names of endocrine glands
and hormones secreted by them.
Answer:
| Endocrine gland | Hormone |
| Pituitary | Growth hormone |
| Thyroid | Thyroxine |
| Adrenal | Adrenaline |
| Pancreas | Insulin |
| Testes | Testosterone |
| Ovaries | Oestrogen & Progesterone |
6. What are sex hormones? Why are they named so? State their function.
Answer:
The hormones involved in the development and control of the reproductive organs and secondary sexual characteristics are called sex hormones. In females the sex hormones produced by the ovary is called oestrogen and in males the sex hormones produced by the testis is called testosterone.
Function
In male, the testes produces the male sex hormone testosterone. This hormone helps in the development and maintenance of the primary and secondary sexual characters and production of sperms.
In female, the ovaries secrete oestrogen and progesterone responsible for the primary and secondary sexual characters.
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: (ii) chapati, dal, vegetables.
8. Write notes on—
(a) Adam’s apple.
Answer:
At puberty, the voice box begins to grow in boys as well as girls. The growth of voice box in boys become much more than the growth of voice box in girls. Due to this, the voice box in boys become much bigger than the voice box in girls.
The bigger voice box in boys gives deeper voice or low pitched voice. The bigger voice box in grown up boy can be seen as a bulge in front of the throat. The bulge or projection at the front of throat or neck in grown up boys is called Adam’s apple. It is formed in grown up boys because of their bigger voice box in the throat. It is called Adam’s apple after the story of Adam and Eve described in the Bible in which Adam ate a piece of forbidden fruit in the Garden of Eden which got struck in his throat. An Adam’s apple sometimes look like a small rounded apple just under the skin in front of throat.
(b) Secondary sexual characters.
Answer:
The sexual characteristics controlled by hormones which distinguish between sexually mature males and female but are not directly involved in reproduction are called secondary sexual characteristics.
The secondary sexual characteristics in males are:
(1) Hairs grow on face in the form of beard and moustache.
(2) Shoulders and chest broadens.
(3) A deeper voice or low pitched voice.
(4) Adam’s apple develops in front of throat in boys.
The secondary sexual characteristics in boys are produced by the male sex hormone called testosterone made in testes.
The secondary sexual characteristics in females:
(1) Development of breast.
(2) Hips broaden and become more curved and prominent in girls.
(3) A shrill or high pitched voice in girls.
The secondary sexual characteristics in girls are produced by the female sex hormone called estrogen made in ovaries.
(c) Sex determination in the unborn baby.
Answer:
The sex of a baby to be born is decided at the moment the egg cell of woman gets fertilised by the sperm of man and pregnancy occurs.The instructions for determining the sex of baby are present in the sex chromosomes which are in the nucleus of the fertilised egg called zygote.
(1) If a sperm carrying X chromosome fertilises an egg cell which carries X chromosomes , then the zygote formed will have XX combination of sex chromosomes due to which the child born will be a girl.
(2) If a sperm carrying Y chromosomes fertilises an egg cell which carries X chromosomes , then the zygote formed will have XY combination of sex chromosomes due to which the child born will be a boy.
The sex of unborn child depends on whether the zygote formed at the time of fertilisation has XX combination of sex chromosomes or XY combination of sex chromosomes.It is the sperm of man that determines the sex of the child.This is because half of the sperms have X chromosomes and other half have Y chromosomes. The egg cells or ova of woman cannot decide the sex of the child because all the egg cells contain the same sex chromosomes , X chromosomes.
(1) If the father contributes X sex chromosomes at fertilisation through its sperm , the baby born will be a girl.
(2) If the father contributes Y sex chromosomes at fertilisation through its sperm, the baby born will be a boy.
Father is responsible for the sex of the baby which is born.
9. Word game : Use the clues to work out the words.
Across
3. Protruding voice box in boys
4. Glands without ducts
7. Endocrine gland attached to brain
8. Secretion of endocrine glands
9. Pancreatic hormone
10. Female hormone
Down
1. Male hormone
2. Secretes thyroxine
3. Another term for teenage
5. Hormone reaches here through blood stream
6. Voice box
7. Term for changes at adolescence
Answer:
Across
3. Adams Apple
4. Endocrine
7. Pituitary
8. Hormone
9. Insulin
10. Estrogen
Down
1. Testosterone
2. Thyroid
3. Adolescence
5. Target site
6. Larynx
7. Puberty
10. The table below shows the data on likely heights of boys and girls as they
grow in age. Draw graphs showing height and age for both boys and
girls on the same graph paper. What conclusions can be drawn from
these graphs?
Answer:
The graph shows the relation between the age and height of both boys and girls. At the time of puberty there is a sudden increase in height of both boys and girls. On the basis of the above graph, it can be observed that during the age of 4-8 years, girls have less height as compared to boys. However, as soon as girl reach 12-13 years, their height shows a sudden increase and become more than boys. In later years, growth in both sexes becomes stable. Growth during puberty is under the control of hormones.
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