NCERT 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 NCERT 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 NCERT Solutions. All NCERT Solutions for class 8 Science are prepared by experts and are 100% accurate.
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Question 1:
The belief that the mother is completely responsible for the sex of the child is wrong because the child
(a) gets sex chromosomes only from the mother.
(b) develops in the body of the mother.
(c) gets one sex chromosome from the mother and the other from the father.
(d) gets sex chromosomes only from the father.
Answer:
A female has two X chromosomes whereas a male has one X and a Y chromosome. If a sperm containing X chromosomes fertilizes the egg, the child will be female as the zygote would have two X chromosomes. If a sperm containing Y chromosomes fertilizes the egg, then the child will be son as the zygote would have one X and a Y chromosome. The sex chromosome of the father is responsible for determining the sex of the unborn child.
Hence, the correct answer is option (d).
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Question 2:
AIDS can spread from an infected person to another person through
(a) sharing food (c) sharing comb
(b) blood transfusion (d) a mosquito bite
Answer:
AIDS can spread from an infected person to another person through blood transfusion. It can also be transmitted through sharing of syringes for injecting drugs, from mother to infant through milk, and by sexual contact with an infected person.
Hence, the correct answer is option (b).
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Question 3:
Given below are events that lead to pregnancy and development of embryo.
(i) Fertilization of egg
(ii) Maturation of egg
(iii) Release of egg
(iv) Embedding of embryo in thickened uterine wall.
Which of the following options gives the correct order of sequence in which they occur?
(a) i, ii, iii, iv, (b) ii, i, iii, iv
(c) i, iv, ii, iii (d) ii, iii, i, iv.
Answer:
Ova or egg is released with the onset of puberty. Ova after maturation is released from one of the ovaries and 28-30 days. In this phase, the uterus wall becomes thick to receive eggs. If the eggs are fertilized by sperm results in the formation of a zygote. This leads to pregnancy. During pregnancy, the zygote begins to divide and then embedded in the uterus for further embryonic development.
Hence, the correct answer is option (d).
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Question 4:
For the metamorphosis of tadpoles which of the following elements must be available in water?
(a) chlorine (c) sulphur
(b) carbon (d) iodine
Answer:
The tadpole passes to several stages to become a frog and the change from larva to become an adult is called metamorphosis. This process in insects is controlled by insect hormone. In frogs, metamorphosis is controlled by the thyroxine hormone that is produced by the thyroid gland. Production of thyroxine hormone from the thyroid gland requires iodine in water. If iodine is not present in sufficient amout in the water in which tadpoles grow, the tadpoles are not able to become frogs.
Hence, the correct answer is option (d).
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Question 5:
The most conspicuous visible change that occurs in boys during puberty is:
(a) development in voice box.
(b) increase in height.
(c) production of sperms.
(d) increased sweating.
Answer:
The most conspicuous visible change that takes place in boys during puberty is an increase in height. It occurs in boys because of the release of the male hormones called testosterone that is responsible for the development of secondary sexual characters in males.
Hence, the correct answer is option (b).
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Question 6:
Structures present in a cell which is responsible for determination of the sex of a baby is
(a) cytoplasm (c) nucleus
(b) cell membrane (d) chromosome
Answer:
A chromosome is a structure that is present in a cell and is responsible for the determination of the sex of a baby. A chromosome is a thread-like structure that is present in the nucleus of every cell. Human beings have 23 pairs of chromosomes in the nuclei of every cell and two chromosomes such as X and Y out of 23 chromosomes are called sex chromosomes. Females have XX chromosome whereas the male has XY chromosome.
Hence, the correct answer is option (d).
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Question 7:
Unscramble the underlined words in the following sentences.
(a) Reproductive life of a woman lasts from hacreemn to spauoemen.
(b) The development of a caterpillar to an adult butterfly is termed as poommertaissh.
(c) The overgrowth of sumselc in xalnyr leads to the hoarse voice in adolescent boys.
(d) Dannalier helps the body to adjust and fight the stress.
Answer:
(a) The reproductive life of a woman lasts from menarche to menopause. Menarche is the first menstrual flow that begins at puberty. Stoppage of menstruation at an age of 45-50 years is called menopause.
(b) The development of a caterpillar to an adult butterfly is termed as metamorphosis. Metamorphosis is a process of change from larvae to an adult and is controlled by insect hormones.
(c) The overgrowth of muscles in the larynx leads to the hoarse voice in adolescent boys. This occurs when muscles present in the voice box grow out of control and the voice becomes hoarse but it remains only for a few days or weeks and after that, the voice becomes normal.
(d) Adrenaline hormone helps the body to adjust and fight the stress. It is often released when a person is stressed, frightened, worried and angry.
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Question 8:
Complete the following sentences.
(a) In females, the uterine wall thickens to receive the __________.
(b) Endocrine glands release hormones directly into ___________ for transportation to the __________.
(c) The sex hormones,_______________________ and estrogen are responsible for the development of __________ characters.
(d) Release of sex hormones is under the control of a hormone secreted from the __________.
Answer:
(a) In females, the uterine wall thickens to receive the egg or ova. The uterine wall in females becomes thickened to receive eggs after fertilization for further development during pregnancy.
(b) Endocrine glands release hormones directly into the bloodstream for transportation to the specific body parts and is called target site.
(c) The sex hormones, testosterone and estrogen are responsible for the development of secondary sexual characters in males and females.
(d) Release of sex hormones is under the control of a hormone that is secreted from the pituitary gland.
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Question 9:
Give a suitable word for each of the following statements.
(a) The site which responds to a hormone.
(b) Name of a gland which transports secretions through ducts.
(c) Chemicals which control changes at adolescence stage.
(d) It marks the beginning of reproductive period.
Answer:
(a) Target site responds to a hormone. Target sites are regions where endocrine glands release hormones into the bloodstream to reach their specific body part.
(b) Exocrine gland are gland that transports secretions through ducts. For example-sweat gland, salivary gland, digestive gland.
(c) Hormones are chemicals that control changes at the adolescence stage.
(d) Puberty marks the beginning of the reproductive period. In this phase, the human body undergoes several changes during adolescence.
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Question 10:
Name the hormone that is released by testes at the onset of puberty.
Answer:
Testosterone hormone is released by testes at the onset of puberty. This hormone is responsible for the development of secondary sexual characters such as the growth of facial hair, deepening of the voice, development of hair on the chest.
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Question 11:
Name the female hormone produced by ovaries that helps in development of mammary glands.
Answer:
Oestrogen is the female hormone that is produced by the ovaries. This hormone is responsible for the development of mammary glands in the breast of the females.
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Question 12:
Match the hormones given in Column A with their deficiency disease given in Column B.
Column A Column B
(a) thyroxine (i) salt imbalance
(b) growth hormone (ii) diabetes
(c) Insulin (iii) goitre
(d) Adrenal hormone (iv) Dwarfism
Answer:
(a)-(iii). Goitre is caused due to the deficiency of the thyroxine hormone by the thyroid gland.
(b)-(iv). Growth hormone is secreted by the pituitary gland that is required for the normal growth of a person and dwarfism is caused due to the deficiency of growth hormone.
(c)-(ii). Diabetes is caused due to the insufficient production of insulin hormone.
(d)-(i). Adrenal glands secrete hormones that are required for the maintenance of correct salt balance in the blood.
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Question 13:
Lila always eats only dal and rice in every meal. She often falls ill and has become prone to diseases. Can you suggest changes in her diet which can make her healthy and free from disease?
Answer:
Lila will have to follow a balanced diet that is rich in protein, carbohydrates, vitamins, and fat in considerable amounts. Lila will include green vegetables, dairy products, nuts, and fruits in her diet as they are rich in all essential nutrients that are required for the proper growth and development of the body.
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Question 14:
Mention any two features each that are seen in boys and girls each to distinguish them from each other at puberty.
Answer:
Changes in girls during puberty-
(i) Development of breast.
(ii) Menstruation begins.
Changes in boys during puberty-
(i) Development of facial hair.
(ii) Increase in height.
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Question 15:
We should avoid taking medicines/drugs unless prescribed by a doctor. Give reasons.
Answer:
We should avoid taking medicines or drugs unless prescribed by a doctor because drugs should be taken in proper dosage otherwise they may harm the body. As they may have some side effects on our health.
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Question 16:
A few of Paheli’s classmates eat potato chips and burgers regularly during the recess at school. Are they healthy eating habits? Give reasons.
Answer:
No, packed and tinned snacks, as well as potato chips, are not considered healthy eating habits because it does not have adequate nutritional content.
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Question 17:
Read the statements given below and fill up the blanks with the correct words listed in the box.
deep, ductless, nutrients, thyroxine
(a) The meal that includes all __________ is a balanced diet.
(b) Insufficient production of __________ in the tadpoles leads to their incomplete development.
(c) Endocrine glands are also called __________ glands.
(d) After attaining puberty boys develop a__________ voice.
Answer:
(a) The meal that includes all nutrients is a balanced diet. It includes protein, carbohydrates, fats, and vitamins in definite proportion.
(b) Insufficinet production of thyroxine hormone in the tadpoles leads to their incomplete development. Thyroxine production requires the presence of iodine in water.
(c) Endocrine glands are also called ductless glands. These glands release hormones directly into the bloodstream to reach a specific body part.
(d) After attaining puberty, boys develop a deep voice. It occurs when muscles of the voice box grow out of control and the voice becomes hoarse.
Page No 56:
Question 18:
Fill the blank circles in the given figure and identify the sex of child A and B.
Answer:
Humans have 23 pairs of chromosomes and out of these 23 pairs of chromosomes, two are sex chromosomes. Females have two X chromosomes and males have one X and one Y chromosome. If the egg is fertilized by sperm containing X chromosome, the child will be girl and if the egg is fertilized by sperm containing the Y chromosome, the child will be a boy.
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Question 19:
During adolescence, the body of boys and girls undergoes certain changes. Given below are a few of those changes.
(a) Broad shoulders
(b) Wider chests
(c) Wider region below waist
(d) Development of muscles
(e) Development of mammary glands
(f) Growth of facial hair
(g) Acne and pimples on face
(h) Development of sex organs
(i) High-pitched voice
(j) Growth of pubic hair.
Categorise these changes into those that occur in boys and those that occur in girls and fill in the table given below.
| Body changes during Adolescence | |
| Boys | Girls |
Answer:
| Body changes during Adolescence | |
| Boys | Girls |
| Broad shoulder | Development of mammary gland |
| Wider chest | High-pitched voice |
| Development of muscles | Wider region below waist |
| Growth of facial hair | Acne and pimple on face |
| Acne and pimples on face | Development of sex organs |
| Development of sex organs | Development of pubic hair |
| Development of pubic hair | |
Page No 57:
Question 20:
In the given Figure mark the positions of the endocrine glands which release the hormones that:
(a) controls the release of sex hormones.
(b) is responsible for the secondary sexual characters in boys.
(c) prevents diabetes.
(d) maintains the correct salt balance in the blood.
Answer:
(a) Pituitary gland controls the release of sex hormones testosterone and estrogen.
(b) Testosterone is responsible for the secondary sexual characters in boys.
(c) Insulin hormone prevents diabetes.
(d) Adrenal gland secretes hormone that helps in the maintenance of correct salt balance in the blood.
Page No 58:
Question 21:
Given below are certain food items required for proper nourishment of adolescents. Name the nutrients present in the food items and write their functions.
| S. No. | Food Items | Major Nutrient | Functions |
| 1. | Pulses and nuts | ||
| 2. | Oranges and Amla | ||
| 3. | Sugar, Roti | ||
| 4. | Oils | ||
| 5. | Vegetables |
Answer:
| S. No. | Food Items | Major Nutrient | Functions |
| 1. | Pulses and nuts | Protein | Helps in the growth and repair of body cells. |
| 2. | Oranges and Amla | Vitamin and iron | Helps in blood formation. |
| 3. | Sugar, Roti | Carbohydrates | Provides energy to the body. |
| 4. | Oils | Fats | Provides energy to the body. |
| 5. | Vegetables | Vitamins and minerals | Helps to keep the body healthy and disease free. |
Page No 58:
Question 22:
Name the hormone which would be released during the following situations:
(a) a frightened person.
(b) growth of a child to adult.
(c) development of caterpillar to moth.
(d) development of tadpole to frog.
Answer:
(a) Adrenaline hormone is produced from the adrenal gland that helps the body to adjust the stress when a person is angry or stressed.
(b) Growth hormone is required for the normal growth of a person.
(c) Insect hormone is responsible for the development of caterpillar to moth.
(d) Thyroxine hormone is responsible for the development of tadpole to frog produced by thyroid gland.
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Question 23:
In human females, each time during maturation and release of egg the inner wall of the uterus thickens. Is this thickening permanent? Give reasons.
Answer:
No, the thickening of the uterus is not permanent because this thickening occurs only when the matured eggs are released from the ovaries to receive eggs for development of an embryo, if fertilization occurs. Thus, if fertilization does not occur, the released egg, thickened lining of uterus along with the blood vessels are shed of and causes bleeding in women. This process is called menstruation.
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Question 24:
John and Radha were classmates since childhood. When Radha became eleven years old, she developed a little swelling on her neck. She visited the doctor who started medication for her. After a few years, John also developed a slight protrusion on his throat. He got worried and went to the doctor. But, the doctor assured him that it was a normal feature in boys while they are growing up. Can you think of any reasons for the difference in diagnosis?
Answer:
John is a boy and at the time of puberty, voice boxes develop larger in boys. It can be seen as a protruding part of the throat called adam's apple. Radha is suffering from goiter. It is a disease of the thyroid gland and is caused because of insufficient secretion of the thyroxine hormone produced by the thyroid gland.
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Question 25:
Observe the chart and graph given in the given Figure carefully and answer the following questions.
Age in % of full height
Years Boys Girls
8 72% 77%
9 75% 81%
10 78% 84%
11 81% 88%
12 84% 91%
13 88% 95%
14 92% 98%
15 95% 99%
16 98% 99.5%
17 99% 100%
18 100% 100%
(a) Which of the line represents the height of boys?
(b) Which line represents the height of girls?
(c) What is the difference between the pattern of increase in the height of boys and girls?
(d) Is this pattern true for each individual?
Answer:
(a) Red line represents the height of boys.
(b) Blue line represents the height of girls.
(c) Girls grow faster than boys by about 18 years of age and both reach their maximum height. The rate of growth in terms of height varies in different individuals.
(d) No, this growth pattern is not true for each individual because growth may vary in different individuals as some may grow suddenly at puberty and then slows down whereas other may grow gradually.
Page No 60:
Question 26:
Salma had a very soft and smooth skin during her childhood. As she entered adolescence, she developed pimples on her face. The skin specialist advised her to wash her face at regular intervals. Can you explain the reasons for the appearance of pimples on her face and suggest ways to prevent them?
Answer:
The secretion of sebaceous glands and sweat glands increases during puberty. Due to this, pimples and acne develop on the face of many girls and boys at this age. The appearance of pimples and acne developed are because of the increased activity of these glands.
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Question 27:
Our government has legalised the age for marriage in boys and girls. Give reasons as to why one should get married after a certain age.
Answer:
The government decided the legal age for marriage in girls is 18 years and for boys is 21 years. The major reason behind this is to stop child marriages. When girls are married at an early age and they give birth to children. Girls are not mentally, emotionally, and physically prepared for this. Early marriage causes problems for both mother and children. It increases mortality rate, more chances of STDs, and mothers, as well as children, become weak and prone to diseases. Boys at an early age are not mentally and financially stable to take the responsibilities of family.
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Question 28:
It is believed that height of a child depends upon the genes inherited from parents. However, it is often seen that tall parents may have short children and vice-versa. Are there factors other than genes, that can cause these variations?
Answer:
Factors other than genes that are responsible for the height of a child are hormones, a balanced diet, exercise, and diseases. A balanced diet is a diet that involves protein, carbohydrates, fats, vitamins, and minerals in the right proportion. It is required for the proper growth and development of the body. Growth hormone is produced by the pituitary gland which is required for the growth of the body. Insufficient production of growth hormone causes dwarfism. Exercise or physical activity is also required for the growth and development of the body as it makes a person fit and free from several diseases.
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