NCERT Exemplar Solutions Class 8 Science Reaching the Age of Adolescence

Multiple Choice Questions..........................

Question 1:  The belief that the mother is completely responsible for the sex of the child is wrong because the child

(a) gets sex chromosome 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 chromosome only from the father. 

Solution 1:  (c) gets one sex chromosome from the mother and the other from the father. 

Mother has a pair of X chromosomes on their 23rd chromosome set, which she still donates to the offspring. On the 23rd set of chromosomes, Father has an XY chromosome. The infant would be female if the father donates the X chromosome. The child would be male if Father donates the Y chromosome. As a consequence, the child's sex is the responsibility of the father.

Question 2: AIDS can spread from an infected person to another person through:

(a) sharing food

(b) blood transfusion

(c) sharing comb

(d) a mosquito bite 

Solution 2: (b) blood transfusion

The following methods can be used to spread AIDS from an infected person:

1. Via the exchange of fluids during sexual activity.
2. By breast milk, from an infected mother to an infant.
3. Using the same needles and syringes.
4. From the infected mother to the unborn child.

Question 3: Given below are events that lead to pregnancy and development of the embryo.

i)Fertilization of egg

ii)Maturation of egg

iii)Release of egg

iv)Embedding of the embryo in the 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 

Solution 3: (d) ii, iii, i, iv

The eggs get mature, then release, and after that it gets fertilized. Embedments of embryo in the thickened uterine walls are the events lead to pregnancy and development of the embryo.

Question 4: For the metamorphosis of tadpoles which of the following elements must be available in the water?

(a) chlorine

(b) carbon

(c) sulphur

(d) iodine 

Solution:  (d) iodine

Thyroxine, a hormone, is responsible for metamorphosis. Iodine is required for the thyroid gland to produce thyroxine. As a result, iodine should be present in water for tadpole metamorphosis.

Question 5:  The most conspicuous visible change that occurs in boys during puberty is:

(a) development in the voice box.

(b) increase in height.

(c) production of sperms.

(d) increased sweating. 

Solution 5: (b) increase in height.

The most noticeable change during puberty is a rise in height. Long bones, such as those in the arms and legs, lengthen at this moment, making an individual taller.

Question 6: Structures present in a cell which is responsible for determination of the sex of a baby is

(a) cytoplasm

(b) cell membrane

(c) nucleus

(d) chromosome 

Solution 6: (d) chromosome

The sex of a child is determined by the 23rd set of chromosomes, known as the sex chromosome. The kid would be a girl if the 23rd set of chromosomes is XX, and a boy if the sex chromosome is XY.

Very Short Answer Questions........................

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. 

Solution 7:

(a) Reproductive life of a woman lasts from menarche to menopause.

(b) The development of a caterpillar to an adult butterfly is termed as metamorphosis.

(c) The overgrowth of muscles in larynx leads to the hoarse voice in adolescent boys.

(d) Adrenalin helps the body to adjust and fight the stress.

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 estrogens are responsible for the development of __________ characters.

(d) Release of sex hormones is under the control of a hormone secreted from the __________. 

Solution 8:

(a) In females, the uterine wall thickens to receive the fertilized egg.

(b) Endocrine glands release hormones directly into the bloodstream for transportation to the target site.

(c) The sex hormones, testosterone and estrogens are responsible for the development of secondary sexual characters.

(d) Release of sex hormones is under the control of a hormone secreted from the pituitary gland.

Question 9: Give a suitable word for each of the following statements.

(a) The site which response to a hormone.

(b) Name of a gland which transports secretions through ducts.

(c) Chemicals which control changes at the adolescence stage.

(d) It marks the beginning of the reproductive period. 

Solution 9:

(a) Target site

(b) Sweat glands/salivary glands/oil glands

(c) Hormones

(d) Puberty

Question 10: Name the hormone that is released by testes at the onset of puberty. 

Solution 10:  Testosterone is a hormone produced by the testes at the start of puberty.

Question 11:  Name the female hormone produced by ovaries that helps in the development of mammary glands 

Solution 11:  Estrogens are a female hormone released by the ovaries that aids in mammary gland growth.

Short Answer Questions........................

Question 12: Match the hormones given in Column A with their deficiency disease given in Column B.

Solution 12:

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? 

Solution 13:   Lila's regular diet consists solely of carbohydrates and proteins. Lila should eat vitamin and mineral-rich foods to remain healthy. She can eat more fruits and vegetables on a regular basis.

Question 14:  Mention any two features each that are seen in boys and girls each to distinguish them from each other at puberty. 

Solution 14:  Two features that are seen in boys at puberty:

1. The voice starts to sound hoarse.
2. Hair growth on the face.

Two features that are seen in girls at puberty:

1. The area under the waist expands.
2. Enlargement of breast.

Question 15:  We should avoid taking medicines/drugs unless prescribed by a doctor. Give reasons. 

Solution 15:  We should not take medications/drugs until they have been prescribed by a doctor because certain medicines have a variety of side effects that can cause adverse effects or contribute to drug addiction, all of which can be harmful to our health and happiness.

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. 

Solution 16:  No, potato chips and burgers are not nutritious because they have so little nutritional value and are not foods that should be consumed on a daily basis.

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 

Solution 17:

(a) The meal that includes all nutrients is a balanced diet.

(b) Insufficient production of thyroxine in the tadpoles leads to their incomplete development.

(c) Endocrine glands are also called ductless glands.

(d) After attaining puberty boys develop a deep voice.

Question 18:  Fill the blank circles in the given figure and identify the sex of child A and B.

Solution 18:

Child ‘A’ is Male.

Child ‘B’ is Female.

Long Answer Questions........................

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) The wider region below the waist

(d) Development of muscles

(e) Development of mammary glands

(f) Growth of facial hair

(g) Acne and pimples on the face

(h) Development of sex organs

(i) High-pitched voice

(j) Growth of pubic hair.

Categorise these changes according to their occurrence in boys and those that occur in girls and fill in the table given below. 

Solution 19:

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. 

Solution 20:

1. Pituitary gland
2. Testis
3. Pancreas
4. Adrenal gland

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.

Solution 21:

Question 22:  Name the hormone which would be released during the following situations:

(a) a frightened person.

(b) growth of a child to an adult.

(c) development of caterpillar to moth.

(d) development of tadpole to frog. 

Solution 22:

(a) Adrenaline hormone is released in a frightened person.

(b) Growth hormone is released at the time of growth of a child.

(c) Insect hormone is responsible at the point of development of caterpillar to moth.

(d) Thyroxine hormone is responsible for the development of tadpole to frog.

Question 23:  In human females, each time during maturation and release of the egg the inner wall of the uterus thickens. Is this thickening permanent? Give reasons. 

Solution 23:  The uterus wall thickening is not permanent. The zygote continues to form after fertilisation and becomes lodged in the uterine wall. This leads to a pregnancy. No more ore eggs are released during pregnancy, but a thickened uterine lining is released after the baby is delivered.

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 diagnoses? 

Solution 24:   Radha's neck swelling may be caused by goitre. Goitre is a disorder in which the thyroid gland releases inadequate amounts of the hormone thyroxine. The swelling of John's neck may be due to Adam's apple, which is caused by the development of the voice box in adolescent boys.

Question 25:  Observe the chart and graph given in below figure carefully and answer the following questions.

(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? 

Solution 25:

(a) Boys' height is shown by the red line.

(b) Girls' height is defined by the blue line.

(c) Girls develop faster than boys at the start of puberty, and by the age of 18 years, they have reached their full height.

(d) No, the pace at which people grow taller differs from one person to the next. Some people grow taller quickly at puberty and then slow down, while others grow slowly.

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? 

Solution 26:  Sweat glands and sebaceous glands secretion increases after puberty. Salma's sweat glands and sebaceous glands secreted more as she approached puberty, resulting in pimples on her face. Salma would be able to get rid of her pimples if she uses a daily face wash to keep her face clean and dry.

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. 

Solution 27:  In India, girls must be 18 years old to marry, while boys must be 21 years old. Before the age of 18, girls are not physically or mentally mature enough to bear a child. Both the mother and the infant would suffer as a result of early motherhood. It is 21 for boys because they are not mentally stable enough and financially secure enough at such a young age.

Question 28:  It is believed that the 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? 

Solution 28:   The height of an individual is not solely determined by hereditary factors. It is dependent on the type of food that they consume, what kind of physical activity they are engaged in. Various growth hormone secretion affect the growth of a child. They are afflicted with a disease at some point in their lives.