Living Science 2019 Solutions for Class 8 Science Chapter 10 Reaching The Age Of Adolescence are provided here with simple step-by-step explanations. These solutions for Reaching The Age Of Adolescence are extremely popular among class 8 students for Science Reaching The Age Of Adolescence Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Living Science 2019 Book of class 8 Science Chapter 10 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Living Science 2019 Solutions. All Living Science 2019 Solutions for class 8 Science are prepared by experts and are 100% accurate.
Page No 132:
Question 1:
State two processes in the body that are controlled by the nervous system and two that are controlled by the endocrine system.
Answer:
The processes that are controlled by the nervous system are as follows:
1. The rate of breathing
2. The rate of heartbeat
The processes that are controlled by the endocrine system are as follows:
1. The amount of sugar in blood
2. Growth and development of an organism
Page No 132:
Question 2:
The nervous system controls body processes by sending messages from the brain through the nerves. How does the endocrine system control body processes?
Answer:
The endocrine system controls different body processes by producing chemical messengers called hormones. These hormones are carried to different parts of the body through blood and they exert different effects, which are responsible for regulating different processes of the body.
Page No 132:
Question 3:
At which stage in a child's life does he/she become an adolescent? What marks the end of adolescence?
Answer:
A child becomes adolescent when he/she reaches the stage of puberty. A boy attains puberty during 11-16 years of age, whereas a girl attains puberty during 10-15 years of age. The end of adolescence is marked by the cessation in further development of the body. Generally, the end of puberty corresponds to the end of adolescence.
Page No 132:
Question 4:
Hormones control the increase in the height of an adolescent and the final height attained. Do you agree? Give reasons.
Answer:
Hormones control the way in which the height of an individual increases during adolescence. The sudden increase in the amount of growth hormone (GH) during adolescence leads to an abrupt increase in the height of an individual. However, the final height attained by an individual depends on the genes of an individual and not on the hormones. This is because genes determine the maximum possible height that can be attained by an individual and hormones only help in the expression of these genes. Thus, hormones do not regulate the final height attained by an individual.
Page No 132:
Question 5:
Pimples appear in those adolescents who do not keep their skin clean. Do you agree? Give reasons.
Answer:
Pimples occur due to hormonal changes that take place during puberty/adolescence. During puberty/adolescence, the activity of sebaceous (oil) glands becomes high. This leads to an increase in the oil production by the skin, which leads to microbial growth on the skin. This microbial growth is the reason for pimples. In order to reduce the growth of microbes, it is essential to keep the skin clean. Thus, the adolescents who do not keep their skin clean experience pimples.
Page No 134:
Question 1:
The menstrual cycle consists of three processes. What are these?
Answer:
The three processes that occur during menstrual cycle are as follows:
1. In the early phase of menstrual cycle, a single ovum (egg) is produced by one of the ovaries. This process is called ovulation.
2. Ovulation is followed by the thickening of the uterus wall which is essential for the reception of egg.
3. In case fertilization does not occur, the lining of the uterus as well as the egg are shed, which is accompanied by bleeding. This period is called menstrual period.
Page No 134:
Question 2:
The sex of a baby is determined by which egg gets fertilized- one containing the X chromosome or one containing the Y chromosome. Do you agree? Give reasons.
Answer:
The sex of a baby is determined by the type of chromosomes present within the nucleus of a fertilized egg. The chromosomes which control the sexual development of an organism are called sex chromosomes. A female has two 'X' chromosomes, whereas a male has one 'X' chromosome and one 'Y' chromosome. Thus, eggs produced a female will have only 'X' chromosomes, but males can produce both 'X' and 'Y' containing sperms. Thus, the sex of a baby is not determined by the egg that gets fertilized.
Page No 134:
Question 3:
Why is iodine essential for metamorphosis to take place properly?
Answer:
The process of metamorphosis is controlled by hormones such as thyroxine. This hormone is produced by the thyroid gland and its synthesis requires the presence of iodine. Thus, iodine is essential for metamorphosis because it is required for the synthesis of thyroxine hormone.
Page No 136:
Question 1:
Which of these processes in the body is controlled by hormones?
(a) blood circulation
(b) growth
(c) digestion
(d) excretion
Answer:
(b) growth
Growth is controlled by hormones in the body.
Page No 136:
Question 2:
Which of these is not a gland of the endocrine system?
(a) adrenal
(b) thyroid
(c) penis
(d) ovaries
Answer:
(c) penis
Penis is the male reproductive organ of humans and not a gland of the endocrine system.
Page No 136:
Question 3:
Which of these is called the master gland?
(a) pituitary gland
(b) testes
(c) thyroid gland
(d) pancreas
Answer:
(a) pituitary gland
Pituitary gland is called the master gland of the endocrine system. It is the gland that controls the activity of many other endocrine hormones of endocrine system.
Page No 136:
Question 4:
Which combination of sex chromosomes is present in a female?
(a) XX
(b) YY
(c) XY
(d) none of these
Answer:
(a) XX
Female cell contains two X chromosomes (XX) while male cell contains one X and one Y chromosomes (XY).
Page No 136:
Question 5:
The stage at which the body becomes capable of reproduction is called
(a) puberty.
(b) menopause.
(c) menstruation.
(d) gestation.
Answer:
(a) puberty
The stage at which the body becomes capable of reproduction is called puberty. It basically refers to the changes in body during sexual maturation.
Page No 136:
Question 6:
The pituitary gland is located
(a) above the kidneys.
(b) in the neck.
(c) at the base of the brain.
(d) near the sex organs.
Answer:
(c) at the base of the brain
Pituitary is a pea-shaped gland located at the base of the brain and is attached to hypothalamus by a stalk.
Page No 136:
Question 7:
Which hormone controls metamorphosis in frogs?
(a) thyroxine
(b) adrenaline
(c) growth hormone (GH)
(d) testosterone
Answer:
(a) thyroxine
Metamorphosis in frogs is controlled by thyroxine. The presence of thyroxine causes the tadpoles to become adult frogs.
Page No 136:
Question 8:
Which of these is not a secondary sex characteristic?
(a) increase in height
(b) release of testosterone
(c) voice change
(d) hair growth on body
Answer:
(a) increase in height
Secondary sexual characters are those features that help to distinguish the male from the female. Hence, increase in height is not a secondary sexual character while release of testosterone, voice change and hair growth on body are secondary sexual characteristics.
Page No 136:
Question 1:
The glands of the __________ system secrete hormones.
Answer:
The glands of the endocrine system secrete hormones.
Page No 136:
Question 2:
Glands release hormones into the blood stream through ducts. True or false?
Answer:
False.
Endocrine glands secrete their product, hormones, directly into the blood stream rather than through ducts. They are also known as ductless glands because they do not have ducts.
Page No 136:
Question 3:
Hormones act wherever they are released by the glands. True or false?
Answer:
False.
Each hormone has a definite function and acts on a particular tissue. They reach their target cell through blood.
Page No 136:
Question 4:
The hormone __________ released by the __________ gland gives sudden energy to the body to fight or run away when in danger.
Answer:
The hormone adrenaline released by the adrenal gland gives sudden energy to the body to fight or run away when in danger.
Page No 137:
Question 5:
In males, the hormone __________ controls sexual characteristics.
Answer:
In males, the hormone testosterone controls sexual characteristics.
Page No 137:
Question 6:
Adolescence is marked by the onset of puberty. True or false?
Answer:
True.
The human body undergoes several changes during adolescence. These changes mark the onset of puberty.
Page No 137:
Question 7:
All parts of the body grow at the same rate during adolescence. True or false?
Answer:
False.
All parts of the body do not grow at the same rate during adolescence. During this time, the body is out of proportion because of growth spurts.
Page No 137:
Question 8:
The larynx is bigger in __________ (boy/girls).
Answer:
The larynx is bigger in boys.
Page No 137:
Question 9:
Adolescents normally sweat more than adults. Is that true or is it a myth?
Answer:
Yes, it is true. Adolescents normally sweat more than adults because the activity of sweat glands increases during puberty.
Page No 137:
Question 10:
Ovulation is the production of an __________ by one of the __________
Answer:
Ovulation is the production of an ovum (egg) by one of the ovary.
Page No 137:
Question 11:
Does a female begin or end her reproductive period at menopause?
Answer:
A female ends her reproductive period at menopause. It occurs at the age of 45–50 years.
Page No 137:
Question 12:
Every sperm has __________ (one/two) sex chromosomes.
Answer:
Every sperm has one sex chromosomes.
Page No 137:
Question 1:
What is the function of the endocrine system? What is it made up of?
Answer:
Endocrine system controls the production and release of hormones, which in turn regulates the various activities of the body.
The two key components of endocrine system are glands and hormones.
Page No 137:
Question 2:
Name four body processes that hormones control.
Answer:
The four body processes that hormones control are growth, development, behaviour and reproduction.
Page No 137:
Question 3:
What hormone does the adrenal glands produce? What is the function of this hormone?
Answer:
The hormone secreted by adrenal gland is adrenaline. It helps in defence of the body in emergency situations. It is also known as emergency hormone or hormone of fight.
Page No 137:
Question 4:
Why is the pituitary gland referred to as the 'master gland'?
Answer:
Pituitary gland is referred to as the master gland of the endocrine system because its hormones control the activity of other glands. It regulates the secretion and release of specific hormones as needed by the body at specific time.
Page No 137:
Question 5:
Name four endocrine glands and the hormones they secrete.
Answer:
Following are the four endocrine glands:
(i) Adrenal gland secretes adrenaline.
(ii) Pituitary gland secretes pituitary hormones such as growth hormone and thyroid-stimulating hormone (TSH).
(iii) Thyroid gland secretes thyroxine.
(iv) Pancreas secretes insulin.
Page No 137:
Question 6:
What do you understand by 'puberty'?
Answer:
Puberty is the stage of life when the body starts to become sexually mature. It starts at the age of 10–15 in girls and 11–16 in boys.
Page No 137:
Question 7:
Why is looking after physical health more important at the adolescent age?
Answer:
Looking after physical health is more important at the adolescent age because rapid physical and mental growth occurs at this stage. For example, during puberty, there is an increased activity of sweat and sebaceous glands due to which personal hygiene becomes very important; otherwise, body odour and bacterial infection may occur.
Page No 137:
Question 8:
What is the final height achieved by an individual primarily governed by? What is the role of hormones in this process?
Answer:
The final height achieved by an individual is primarily governed by the genes that they inherit from their parents. The hormones help in achieving the normal adult height.
Page No 137:
Question 1:
What are the functions of the pituitary gland? List two hormones it produces and give their functions.
Answer:
Functions of the pituitary gland:
(i) It regulates many body functions through the hormones it releases.
(ii) It influences the functioning of the other glands.
Hormones released by the pituitary gland and their functions:
(i) Growth hormone (GH): It is involved in the growth and development of the body.
(ii) Thyroid-stimulating hormone (TSH): It stimulates the thyroid gland to release thyroxine.
Page No 137:
Question 2:
Discuss they way height in adolescents increases.
Answer:
In adolescents, there is a sudden increase in height. It is brought about by elongation of the bones of the arms and the legs. The rate of growth in height varies in different individuals. While some children grow suddenly at puberty and then slow down, others grow gradually.
Page No 137:
Question 3:
What causes pimples to appear in adolescents?
Answer:
During adolescence, there is an increased secretion of sebum (oil) from the sebaceous gland. This makes the skin oilier and leads to the appearance of pimples on the face of adolescents.
Page No 137:
Question 4:
What changes occur in the body shapes of boys and girls at adolescence?
Answer:
Following changes occur in body shapes:
In boys,
(i) Shoulders broaden
(ii) Chest widens
(iii) Body develops muscles
In girls,
(i) Pelvic region widens
(ii) Hips broaden
(iii) Breasts develop and increase in size
Page No 137:
Question 5:
Why do adolescents often find themselves confused and insecure?
Answer:
During adolescence, children go through many mental and emotional changes. They start thinking more maturely and become more independent than before. They tend to spend a lot of time thinking. Sometimes, they face difficulty in adjusting to the changes that occur in their minds and bodies. As a result, they often find themselves feeling confused, insecure and self-conscious.
Page No 137:
Question 1:
Discuss the changes in the voices of boys and girls during adolescence.
Answer:
During adolescence, the larynx gets bigger and the vocal cords are lengthened and thickened. This makes the voice deeper in boys. The increased larynx occurs as a protruding part in some boys and is known as Adam's apple. Sometimes, the muscles of the growing larynx go out of control and the voice grows hoarse; however, it becomes normal after some time. In girls, the larynx grows bigger as well, but the growth is not as much as in boys. Generally, girls have a high-pitched voice because of this change.
Page No 137:
Question 2:
Discuss the menstrual cycle.
Answer:
The cycle of producing and releasing mature eggs or ova is called menstrual cycle. The end of cycle is accompanied by the breakdown of the lining of uterus that gets released in the form of blood and mucus through the vagina. It takes around 28 days to complete.
The menstrual cycle starts at the age of 10–15 years (menarche) and the cycle stops at the age of 40–50 years (menopause).
Page No 137:
Question 3:
Explain what determines the sex of a baby.
Answer:
The sex of a baby is determined by the type of sperm that fertilises the ovum.
(i) If the sperm-carrying X chromosome fertilises the egg, it would be a baby girl, because the chromosome pair will be XX after fertilization.
(ii) If the sperm-carrying Y chromosome fertilises the egg, it would be a baby boy, because the chromosome pair will be XY after fertilization.
Page No 137:
Question 4:
How should an adolescent look after his/her physical health?
Answer:
During adolescence, there is rapid mental and physical growth. Thus, it is necessary for adolescents to take care of their physical health.
(i) Take a balanced diet containing the right amount of carbohydrates, proteins, fats, vitamins and minerals.
(ii) Do not consume fast food as a substitute for meals, for in spite of the good taste such food lack adequate nutrition.
(iii) Maintain proper personal hygiene. Due to increased activity of sweat and sebaceous glands, proper cleaning of body is essential; otherwise, it may lead to body odour and bacterial infection. Girls should especially be careful about hygiene during menstruation.
(iv) Engage in physical exercises like walking, jogging and aerobics that keep the body physically and mentally fit.
Page No 137:
Question 1:
Many adolescent boys look awkward and disproportionate. Why is that so?
Answer:
Many adolescent boys look awkward and disproportionate because during puberty, their bodies go through various changes. For example, some parts of the body like the hands and feet grow faster than arms and legs. Also, due to increased activity of hormones, pimples start to appear that may remain throughout the teenage years.
All these changes at puberty make adolescents feel awkward and clumsy. However, eventually, all these changes disappear and soon the body regains its normal proportions.
Page No 137:
Question 2:
Why do you think the pelvic area in girls broadens at puberty?
Answer:
The pelvic area in girls broadens at puberty because they have to bear a baby in their uterus later in their life.
Page No 137:
Question 3:
Drugs are harmful at all ages. Why do we then specifically emphasise that adolescents should avoid drugs?
Answer:
Adolescents are more prone to drugs. As they go through many mental and emotional changes during adolescence, they may start consuming drugs in order to overcome negative emotions (such as stress, pressure, depression and frustration) and to excel in various fields. Sometimes, curiosity, need for adventure and excitement and experimentation also lead to consumption of drugs by adolescents.
As drugs are inherently addictive, adolescents taking such substances become dependent on them. This can lead to health problems and indulgence in criminal activities.
Page No 138:
Question 1:
The graph given below shows how the lining of the uterus in a female who has achieved puberty varies with time.
Examine the graph and answer the following questions.
1. What is happening between A and B?
2. Mark the corresponding points in the second menstrual cycle when the same happens.
3. Fertilization occurs on day 16 of the second menstrual cycle. How do you expect the graph to behave after point C? Will the pattern of the first and second months be followed?
Answer:
1. The period between A and B represents the menstrual flow. During this phase the uterus lining is shed along with blood and moves out of the body in the form of bleeding.
2. The points I and II correspond to the period when bleeding/menstrual flow will occur.
3. Since fertilisation occurs on day 16, the graph after point C will be straight lined. It is because, once fertilisation occurs, the uterus lining is retained and no bleeding/menstrual flow occurs during that period.
Page No 138:
Question 1:
Ramesh studies in Class 10. He says he would like to try alcohol and drugs just to see what they are like. Is he correct in doing this? What advice would you give him?
Answer:
No, Ramesh is wrong. Most of the adolescents get addicted to alcohol and drugs on the pertext of trying them. It is one of the major reasons why most of the adolescents fall into the trap of alcohol and drugs.
I would advice him to stay away from such things and also talk to him about their ill effects.
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