Class 8 Science Chapter 7 Question Answers - Reaching the Age of Adolescence

Q1: Adolescence is also a period of change in a person’s way of thinking. Justify the statement.  

Ans: Adolescence are more independent than before and are also self-conscious, during adolescence intellectual development take place and teenagers tend to spend considerable time in thinking, infact it the time when brain has the greatest capacity of learning. Sometimes adolescent may feel more attraction towards opposite sex because of release of sex hormones and they may also feel insecure while trying to adjust to the changes in mind and body, but they should understand that these changes are natural part of growing up.
Q2: Explain changes occuring in human body at puberty.

Ans: 
1. There is sudden increase in height during puberty, at this time the bones of arms and legs elongate and make a person tall.

2. There is change in body shape during puberty which includes broader shoulder and wider chests in boys and in girls region below the waist becomes wider.
3. In boys, at puberty, there develop a larger voice box which can be seen as a protruding part of the throat called Adam’s apple. Sometimes the muscles of the growing voice box go out of control and the voice becomes hoarse.
4. The increased secretion of sweat and sebaceous gland in the skin causes acne and pimples on the face of young people.
5. At puberty male sex organs like testes and penis develop completely, the testes also begin to produce sperms, in the girls ovaries enlarge and starts releasing mature eggs, these are mainly controlled by hormones like testosterone in male and estrogen in female.

6. During puberty many features develops in boys and girls that help to distinguish male from female, which is called secondary sexual character. This causes changes in boys like production of sperms, growth of beard and moustaches, growth of hair on chest, under the arms and in pubic region, this causes changes in girls like production of ova, development of breast, development of mammary gland inside the breast, growth of hair under the arms and in pubic region.
Q3: Explain secondary sexual characters and roles of hormones in initiating reproductive function

Ans: During puberty many features develops in boys and girls that help to distinguish male from female, which is called secondary sexual character. This causes changes in boys like production of sperms, growth of beard and moustaches, growth of hair on chest, under the arms and in pubic region, this causes changes in girls like production of ova, development of breast, development of mammary gland inside the breast, growth of hair under the arms and in pubic region.
The changes occuring in body at adolescence is mainly controlled by the action of hormones. Hormones are chemical substance secreted by endocrine gland that reaches to a particular body part via bloodstream. Changes in boys like production of sperms, growth of beard and moustaches, growth of hair on chest, under the arms and in pubic region are all because of release of male hormone testosterone and changes in girls like production of ova, development of breast, development of mammary gland inside the breast, growth of hair under the arms and in pubic region are all because of the female hormone estrogen produced by ovaries.
Hormones from endocrine glands like testes and ovaries stimulates testosterone in male and estrogen in female respectively .These hormones are released in bloodstream and they reaches to their target sites that is the particular body parts where they have to show their effects, the target sites respond to the hormone and it stimulate to the changes in the body at onset of puberty. Thus we can say that the onset of puberty is controlled by hormones.

Q4: How do hormones work? Explain with the help of a flow chart.
Ans.

Q5: Explain the sex determination of a baby in human.
Ans. Inside the fertilised egg or zygote is the instructor for determination of sex of the baby. The instruction is present in the chromosomes in the fertilised egg. All human beings have 23 pairs of chromosomes in the nuclei of their cells. Out of these chromosomes 

two chromosomes are the sex chromosomes named X and Y. A female has two X chromosomes while a male has one X and one Y chromosomes. The eggs and sperms have only one set of chromosomes. The unfertilised egg always has one X chromosome.  But sperms are of two kinds. One kind has an X chromosome and other kind has Y chromosome. When a sperm containing X chromosome fertilises the eggs the zygote develops into a female child. If sperm contributes a Y chromosome to the egg at fertilisation, the zygote develops into a male child.

Q6: What are endocrine glands? Write the names of hormones and the functions of thyroid, pancreas and adrenal glands.
Ans. The glands which have no any duct to pour their secretions (hormones) into blood directly are called endocrine glands.
Thyroid: Thyroid is the endocrine gland. It secretes thyroxine hormone. If thyroid does not produce thyroxine, then thyroid glands increase in size and cause a disease called goitre.
Pancreas: Pancreas is also an endocrine gland which produces insulin hormone. If insulin is not produced sufficient then a person suffers from a disease called diabetes.
Adrenal: The hormone produced by adrenal gland is called adrenalin. This hormone maintains the correct salt balance in the blood. It also adjusts the body to stress when one is very angry, embarrassed or worried.

Q7: What do you mean by health? What are the factors which help to keep a good health?
Ans. The physical and mental well being of an individual is regarded as health.
The factors that help to keep a good health:
(i) One should take a balanced diet.
(ii) One should care and keep personal hygiene.
(iii) Walking and playing in fresh air keeps the body fit and healthy.
(iv) All young boys and girls should take walks, exercise and play outdoor games to keep good health.
(v) Avoid the alcohol and tobacco.
(vi) Drink clean water, breathe in clean air and eat clean food.