Q.1 What is the term used for secretions of endocrine glands responsible for changes taking place in the body?
NCERT Solutions for Class 8 Science Chapter 10 Reaching The Age Of Adolsence
Answer :
Hormones are used for secretions of endocrine glands and are responsible for changes taking place in the body.
A hormone is a member of a class of signaling molecules in multicellular organisms, that are transported to distant organs to regulate physiology and behaviour.
The main function of endocrine glands is to secrete hormones directly into the bloodstream to serve as messengers, controlling and coordinating activities throughout the body.
NCERT Solutions for Class 8 Science Chapter 10 Reaching The Age Of Adolsence
Answer :
Adolescence is a transitional stage of physical and psychological development that generally occurs during the period from puberty to legal adulthood.
The period of life when the body undergoes changes, thus leading to reproductive maturity, is called adolescence.
The period of adolescence is normally between 11 to 19 years of age.
NCERT Solutions for Class 8 Science Chapter 10 Reaching The Age Of Adolsence
Answer :
Menstruation is the process of the shedding of the uterine lining which is basically the blood lining, on a regular monthly basis.
It begins at puberty when the female individual starts producing ovum. The ovum is released into the fallopian tube and waits till it gets fertilized by a sperm, otherwise it sheds along with the blood vessels during menstruation.
The blood vessels develops in the uterine lining in the form of a cushion to receive a fertilized egg. As a result the inner lining of the uterus becomes thick and is supplied with blood to nourish the growing embryo. If the ovum is not fertilized, then the lining of the uterus breaks down and gets released in the form of blood through the vagina. This lasts for about two to eight days. As the cycle occurs every month, so it is known as the menstrual cycle.
NCERT Solutions for Class 8 Science Chapter 10 Reaching The Age Of Adolsence
Answer :
Changes in the body that take place at puberty are as follows:
(i) There is sudden increase in height and weight of adolescents.
(ii) There is broadening of shoulders and widening of chest in boys while the region below waist becomes wider in case of girls.
(iii) Due to hormonal changes the larynx becomes prominent and the vocal cords become longer and thicker which causes the voice to become hoarse. In case of boys, this increase of vocal cord is visible and hence called as Adam's apple.
(iv) There is growth of hair in areas such as underarms, pubic region, face, hands, and legs. Boys grow moustache and beard while girls have a increase in the size of their breast.
(v) There is appearance of acne as a result of excessive secretion of oil from skin in both boys and girls.
(iv) Testis grows and starts producing sperms in males whereas the ovary enlarges and starts producing ovum in case of girls.
NCERT Solutions for Class 8 Science Chapter 10 Reaching The Age Of Adolsence
Answer :
Sex hormones are chemical substances produced by primary sex organs thus affecting the development of secondary sexual characters and reproduction.
Testosterone is the male sex hormone produced by the testis and estrogen is the female sex hormone produced by the ovary. As they develop the sexual characteristics of an organism, hence they are known as sex hormones.
Testosterone:
This hormone develops secondary sexual characters in boys such as the growth of beard, hoarseness of the voice, development of secondary reproductive organs, etc. It also regulates bone mass, fat distribution, muscle mass, strength and the production of red blood cells and sperm.
Estrogen:
This hormone develops secondary sexual characters in females such as the enlargement of breasts, development of female reproductive organs and pubic hair etc. It keeps cholesterol in control and protects bone health and also maintains the menstrual cycle and ovum production.
Q.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.
(b) Reproductive age in women starts when their:
(i) menstruation starts.
(ii) breasts start developing.
(iii) body weight increases.
(iv) height increases.
(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.
NCERT Solutions for Class 8 Science Chapter 10 Reaching The Age Of Adolsence
Answer :
(a) Adolescents should be careful about what they eat, because :
(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.
(c) The right meal for adolescents consists of :
(ii) chapati, dal, vegetables.
Q.8 Write notes on:
(a) Adam’s apple
(b) Secondary sexual characters.
(c) Sex determination in the unborn baby.
NCERT Solutions for Class 8 Science Chapter 10 Reaching The Age Of Adolsence
Answer :
(a)Adam’s apple
When there is an increase in the size of the larynx during puberty, it sticks out at the front of the throat. Everyone's larynx grows during puberty, but a girl's larynx doesn't grow as much as a boy's larynx grows. As boys' larynx grows more, it makes their voices deeper than girls' voice. In boys, the voice box tends to protrude out on the upper part of the neck, below the chin and is referred as Adam’s apple.
(b) Secondary sexual characters.
Secondary sexual characteristics are the features that appear during puberty in humans, and at sexual maturity in other animals. These characters are visible more apparently and thus help in distinguishing a male from a female. In humans, visible secondary sexual characteristics include pubic hair, enlarged breasts and widened hips in females and facial hair and Adam's apple in males.
(c) Sex determination in the unborn baby.
Every human has two types of chromosomes i.e., autosomes and sex chromosomes. There are 22 autosomes and 2 types of sex chromosomes i.e., X and Y. There is a total of 23 pairs of chromosomes in an individual.
A male individual has 44 autosomes and XY sex chromosomes while a female individual has 44 autosomes and XX sex chromosomes.
So if a male gamete(sperm) containing 22 autosomes and X chromosome fuses with a female gamete(ova/egg) containing 22 autosomes and X chromosome, then the zygote contains a total of (44 + XX) chromosomes, thus later forming a female child.
And if a male gamete(sperm) containing 22 autosomes and Y chromosome fuses with a female gamete(ova/egg) containing 22 autosomes and X chromosome, then the zygote contains a total of (44 + XY) chromosomes, thus later forming a male child.
As the sex of a child depends on the type of male gamete containing either X or Y chromosome, hence the sex determination of a child depends on the father.
NCERT Solutions for Class 8 Science Chapter 10 Reaching The Age Of Adolsence
Answer :
Q.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?
NCERT Solutions for Class 8 Science Chapter 10 Reaching The Age Of Adolsence
Answer :
The graph shows the relation between the age and height of boys and girls with a comparison between both of them.
From the above graph, we conclude that initially boys grow faster than girls from 0-8 years.
At reaching puberty, both has a sudden rise in their height, though the girls grow faster than boys from 8-16 years.
Both reach their maximum height at the age of 20. Here the boys show a greater increase in height than girls.
Now, growth in both of them comes to a halt, upon reaching the end of adolescence as the hormonal changes and their secretions had become stable at this point.