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

Ans: Adolescence is the period of life when a body undergoes changes leading to reproductive maturity. These changes mark the onset of puberty.

Ans: 

(a) Adolescene: Human beings become capable of reproduction after the puberty sets in. The period of life when the body undergoes changes, leading to reproductive maturity, is called adolescence. Between the age of 11 years and 19 years children are called adolescents.
(b) Puberty: Puberty is the process of physical changes by which a child's body matures into an adult body and it becomes capable of sexual reproduction to enable fertilisation.The human body undergo several changes during adolescence; these changes mark the onset of puberty

Ans: 
(a) Adam’s apple: 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.
(b) Secondary sexual characters: 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.

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

Ans: 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.

Ans: 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.

Ans: The increased secretion of sweat and sebaceous gland in the skin causes acne and pimples on the face of young people.

Ans: 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.

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.

Ans: 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.

Ans: 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.

Ans:  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.

Ans: Testosterone is the male hormone and estrogen is the female hormone. The uterine wall in females prepares itself to receive the developing fertilised egg. In case if there is no fertilisation, the thickened lining of uterine wall breaks down and goes out of body along with blood, this is called menstruation. Menarche is the first menstrual flow which begins at puberty and stoppage of menstruation is called as menopause.

Ans: Female has two X chromosome while male has one X and one Y chromosome. The unfertilised egg has only one X chromosome but sperm are of two kinds one has X chromosome and other has Y chromosome, when sperm containing X chromosome fertilises with egg the zygote would have two X chromosomes and develop into female, similarly when sperm containing Y chromosome fertilises with egg the zygote would have one X and one Y chromosomes and develop into a male child.

Ans: Under secretion of Insulin causes diabetes, thyroxine under secretion causes goitre.

Ans: The production of all hormones is under the control of pituitary gland.The pituitary gland is termed the "Master Gland" because it directs other organs and endocrine glands, such as the adrenal glands and thyroid glands to suppress or induce hormone production, it involves following functions

• Growth Hormone Production
• Production of Hormones That Act on Other Endocrine Glands
• Production of Hormones That Act on the Muscles and the Kidneys
• Endocrine Function Regulation
• Storage of Hormones Produced by the Hypothalamus

Ans: The life cycle of insects involves four different stage namely, egg, larva, pupa and adult. The changes from larva to adult is called metamorphosis, in insects metamorphosis is controlled by insects hormones in the same way in frog tadpole became a frog under the action of thyroxine hormone produced by thyroid.

Ans: Adolescence is the phase of growth and development of different body parts, thus it requires a complete healthy food that is the balanced diet.

Ans: Walking and playing in fresh air keeps the body fit and healthy. All youngsters should take walks, exercise and play outdoor games to keep themselves fit and for the proper growth and development of body.

Ans: Take bath regularly, wash and clean all body parts every day. Use clean towel to wipe yourself, females should take special care of cleanliness during menstrual flow.

Ans: The under secretion of insulin hormone by pancreas leads to increase in blood glucose level and causes diabetes in human beings.

Ans: The under secretion of thyroxine hormone by thyroid gland causes swelling of thyroid gland which causes swelling of the neck or larynx which is called as goitre.

Ans: AIDS is caused by a dangerous virus called HIV , this virus can pass on to a normal person from an infected person by Infected blood, Infected needles, multiple partners, Infected mother to her baby before birth, Injectable Drug Abuse.

Ans: Growing up is a natural process. The period of life, when the body undergoes changes, leading to reproductive maturity is called adolescence.

Ans: Adolescence begins around the age of 11 and lasts up to 18 or 19 years of age. Since this period covers the teens (13 to 18 or 19 years of age) adolescence is also called teenage.

Ans: The human body undergoes several changes during adolescence. These changes mark the onset of puberty. The most important change which marks puberty is that boys and girls become capable of reproduction.

Ans: Present height = 120 cm %age of height at this age = 75. So, height at the end of growth period

Ans: There are following two factors which affect the height:
(a) Genes inherited: The height of an individual is more or less similar to that of his or her parents. The height depends on the genes inherited by the parents.
(b) Height also depends on the diet taken by the person in this growing period.

Ans: In boys, the shoulders become broader and chests become wider in the age of adolescence. In girls the region below the waist becomes wider.
In boys the muscles of the body grow more prominently than in the girls. The changes occurring in adolescent boys and girls are different.

Ans: At the puberty, male sex organs like testes and penis develop completely. The testes also begin to produce sperms. In girls, the ovaries enlarge and eggs begin to mature. Ovaries also start releasing mature eggs. 

Ans: Sometimes boys and girls have improportionate body parts. They look tall but face looks smaller. This is because all body parts do not grow at the same rate. But slowly they all catch up and body becomes balanced.

Ans: The voice box or larynx begins to grow. The growing voice box in boys can be seen as a protruding part of the throat, called Adam’s apple. In girls the larynx is hardly visible from the outside because of its small size. Girls have high pitched voice, whereas boys have a deep voice.

Ans: During puberty, the secretions from sweat glands and sebaceous glands increase. Many young people get acne and pimples on the face at this time because activity of these glands in the skin increase.

Ans: In girls, breasts begin to develop at the time of puberty. These features help us to distinguish the male from the female. These characters are called secondary sexual characters. Hair grows under the arms and in the region above the thighs or the pubic regions in girls.

Ans: The facial hair begin to grow in boys, that is moustaches and beard. Boys also develop hair on their chest. Hair grows under the arms and in the region above thighs or pubic region in boys like the girls.

Ans: The changes which occur during puberty are controlled by hormones. The hormones are the chemical substances. These are secretions from endocrine glands or endocrine system. These hormones are secreted from ovary, testes or pituitary gland at the time of puberty. The hormones secreted by pituitary stimulate testes and ovaries to secrete male and female hormones respectively.

Ans: Hormones are released by endocrine glands into blood stream to reach a particular body part called target site. The target site responds to the hormone. There are many endocrine glands or ductless glands in the body.

Ans: In girls, estrogen causes the development of mammary glands. They develop inside the breast and cause enlargement of breasts. In boys testosterone is secreted by testes and it causes growth of moustaches and beard.

Ans: At the time of maturation of ovaries the eggs are released by these ovaries. One egg is released at a time. If this egg is not fertilized, the released egg and thickened lining of the uterus along with its blood vessels are shed off. This causes bleeding in women which is called menstruation. Menstruation occurs once in about 28 to 30 days.

Ans: Menarche: The first menstrual flow beginning at puberty is termed as menarche.
Menopause: At 45 to 50 years of age the menstrual cycle stops. Stoppage of menstruation is termed as menopause.

Ans: In case the egg is fertilized it begins to divide and then gets embedded in the uterus for further development. At last the fertilized egg is developed into a foetus.

Ans: Pituitary gland is called master gland. It is the most important endocrine gland. The hormones secreted by the pituitary gland stimulate testes and ovaries to produce their hormones. Pituitary gland also controls the secretions of other endocrine glands. It is attached to the brain.

Ans: The changes from larva to adult is called metamorphosis. Metamorphosis in insects is controlled by insect hormones. In a frog it is controlled by thyroxine, the hormone produced by thyroid. Thyroxine production required the presence of iodine in water. If the water in which the tadpoles are growing does not contain sufficient iodine, the tadpoles cannot become adults.

Ans: AIDS is caused by a virus named HIV. It can be transmitted from an infected person to a healthy person by following ways:
(i) By infected syringes.
(ii) By infected mother to an infant.
(iii) By sexual contact with infected person.

Ans: The myths which are not facts:
(i) A girl becomes pregnant if she looks at a boy during menstruation.
(ii) The mother is responsible for the sex of her child.
(iii) A girl should not be allowed to work in the kitchen during menstruation.