NCERT Class VIII Science Solutions: Chapter 10-Reaching the age of Adolescence Part 6

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Question 22:

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

  1. A frightened person.

  2. Growth of a child to adult.

  3. Development of caterpillar to moth.

  4. Development of tadpole to frog.

Answer:

  1. Adrenaline is secreted from adrenal gland during the stress conditions like fright or fear fright or fear, anger, worry or embarrassment. The hormones prepare prepares the body to function at maximum efficiency by increasing the heart beat and breathing rate, raising B.R. etc.

    Image of Adrenaline

    Image of Adrenaline

    Image of Adrenaline

  2. Growth hormone is secreted from pituitary gland to regulate the normal growth of a person, growth of a child to adult. Its deficiency in childhood makes a person dwarf, while its excess makes a person very tall.

  3. Insect hormones control the development of caterpillar to moth, i.e. metamorphosis.

  4. Thyroxine is produced by thyroid gland to control the development of tadpole to frog. Iodine in water is necessary for its production.

Question 23:

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

Answer:

No, this thickening of the uterine wall is not permanent.

If the egg gets fertilized, it starts developing and gets embedded in the uterine wall resulting in pregnancy. During pregnancy no more eggs are released and the thickened lining is discharged only when the baby is born. However, if fertilization does not occur, the released egg and the thickened lining are shed off resulting in menstruation

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?

Answer:

The swelling on the neck of Radha may have been because of goiter, a condition of the thyroid gland during which the gland produces insufficient quantity of thyroxine. However, the protrusion in John’s throat would be Adam’s apple, a result of growth of voice box in adolescent boys.

Question 25:

Observe the chart and graph given in Fig carefully and answer the following questions

Percentage of Full Height
Percentage of full height

Age in Years

% of full height

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%

Result for Line Chart

Line Chart

Result for Line Chart

  1. Which of the line represents the height of boys?

  2. Which line represents the height of girls?

  3. What is the difference between the pattern of increase in the height of boys and girls?

  4. Is this pattern true for each individual?

Answer:

  1. The red line represents the height of boys.

  2. The blue line represents the height of girls.

  3. At the onset of puberty, girls grow faster in height than the boys and by the age of 18 years, approximately both reach their maximum height.

  4. No, the rate of growth in height varies among individuals. Some may grow in height suddenly at puberty and then slow down, while others may grow gradually.

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