Reaching the Age of Adolescence For Class 8 Science Important Question Answer

Ans. (b) 11 to 19 years

Ans. (b) 23 pairs

Ans. (c) testosterone

Ans. (b) hormones

Ans. (a) Adrenalin

Ans. (c) menarche

Ans.  (b) adolescence

Ans.  (a) Voice box

Ans.  (b) Metamorphosis

Ans.  (d) 45-50 years in women

Ans. (d) Males only

Ans. (d) Adolescent boys

Ans. (a) one X and one Y

Ans. (d) Testis

Ans. (c) 11 – 19 years

Ans.  (d) 18 – 19 years

Ans.  (a) 10 – 12 years

Ans. Growing up is a natural process. The period of life, when the body undergoes several changes leading to reproductive maturity, is cabled adolescence. The adolescence period is 11 to 19 years of age.

Ans. During puberty, the human body undergoes several changes, but the most important changes which marks puberty is that boys and girls become capable of reproduction.

Ans. Body shape changes differently in boys and girls at puberty. Boys have broader shoulders and wider chests. Their muscles grow more prominently than girls. In girls, the region below the waist becomes wider.

Ans. During puberty the secretion of sweat glands and sebaceous glands (oil glands) increases. It develops acne and pimples on the face of young boys and girls.

Ans. At puberty, in girls, breasts begin to develop, the region below the waist become wider, voice become shriller. Boys begin to grow facial hair, i.e., moustache and beard. Boys also develop hair on their chest, the muscles of the body grow more prominently, develop larger voice box which can be seen as a protruding part of the throat called Adam’s apple. In both boys and girls, hair grows under the arms and in the pubic region. As these features distinguish the male from the female they are called secondary sexual characters.

Ans. The changes in human body at puberty occur due to release of hormones by different types of glands. Hormones are chemical substances secreted from endocrine glands or endocrine system. Male hormone or testosterone are responsible for changes in male whereas female hormone or estrogen are responsible for changes in female.

Ans. Endocrine glands release hormones into the blood stream to reach a particular body part called target site. The target responds to the hormone. There are many endocrine glands or ductless glands in the body.

Ans. At puberty, in girls the ovaries get enlarged and start producing eggs (ovum). One egg matures and is released by one of the ovaries once in about 28 to 30 days. During this period, the wall of the uterus becomes thick so as to receive the egg. If the egg is fertilised then it begins to develop and results in pregnancy. If this egg is not fertilised, the released egg and thickened lining of the uterus along with its blood vessels are shed off causing bleeding in female which is called menstruation. It occurs once in about 28 to 30 days.

Ans. There are several changes in females at the onset of puberty. They are:

• growth of hair in armpit and pubic region.
• development of breasts and mammary glands.
• ovaries get enlarged and begin producing eggs.
• menstruation cycle starts; and
• increased activity of sweat and sebaceous glands.

Ans. There are various changes in males at puberty. They are:

• sudden increase in height.
• growth of hair at different parts of body like face, armpit and pubic region, development of moustache and beard.
• development of Adam’s apple in throat, voice becomes hoarse.
• shoulders become broader and chest wider.
• growth of size of reproductive organs like penis, testes begin to produce sperms, etc.

Ans. Hormones play an important role in the completion of life cycle of insects and frogs. Metamorphosis in insects is controlled by insect hormones. In a frog, it is controlled by thyroxine, the hormone produced by thyroid gland. Thyroxine production requires the presence of iodine in water. Water in which iodine is not, present, the tadpoles cannot become adult.

Ans. There are various changes in human at puberty. They are as follows:

• Change in height: During puberty, there is sudden increase in height in boys and girls. Initially, girls grow faster in height than in boys. But both reach their maximum height at the age of 18 years.
• Change in voice: Boys develop larger voice box or larynx to form protruding part of throat called Adam’s apple making their voice hoarse, girls have high pitched voice.
• Change in body shape: In boys, shoulders broaden and muscles grow more prominently than in girls. In girls the region below the waist becomes wider.
• Secretion of sweat and sebaceous glands (oil glands) in both boys and girls increases and acne or pimples grow on faces of many youths.
• Development of sex organs: In males, testes and penis develop completely. Testes begin producing sperms. In girls, ovaries are enlarged and begin to produce eggs. Both boys and girls reach reproductive maturity.
• In girls, menstruation or periods starts.
• All human beings attain mental, intellectual and emotional maturity at puberty.
• Facial hair like moustache and beard are grown in boys. Hair are grown in armpit and pubic region in both boys and girls. Breasts are developed in girls. These characters are called secondary sexual characters as they distinguish a male from a female.

Ans. There are different types of glands in our body and they secrete different types of hormones which control groftoth, behaviour, development and reproduction. The following table shows different types of glands, hormones secreted by them and their functions:

Q 31 – Explain sex determination in human.

Ans.

Sex determination of a baby is done at the time of fertilisation when a male gametes fuse with a female gamete. It depends on male partner whether the baby will be a male child or female child. The chances of child to be male or female actually depend on the chromsomes present in the fertilised eggs or ova. There are 23 pairs of chromosomes in the nuclei of all human beings out of which two are sex chromosomes named X and Y. A male has one X and one Y chromosome and a female has two X chromosomes. The gametes (egg and sperm) have only one set of chromosomes. The unfetilised egg always has one X chromosome. But sperms are of two kinds. One kind has an 

When a sperm containing X chromosome fertilises the egg, the zygote would have two X chromosomes and develop into a female child. If the sperm contributes a Y chromosome to the egg (ovum) at fertilisation, the zygote would develop into a male child. Fig. 10.5 shows sex determination in humans.

Ans. The state of physical, mental and social well being of an individual is regarded as an individual’s health. A healthy person is free from disease, tension and anxiety. Reproductive health refers to a state of physical, mental and social well-being in all matters relating to the reproductive system, at all stages of life. We should take following measures to maintain reproductive health:

• To have a balanced diet: As far as practicable, we should have a balanced diet, i.e., a diet contain¬
  ing proteins, vitamins, carbohydrates, fats and minerals. We can have our food which contain these nutrients.
• To take physical exercise: We should take physical exercise like morning walk, running, etc., daily.
• To maintain personal hygiene: We should maintain personal hygiene to stay fit and healthy. We should wash our body especially pubic region, armpit, etc., properly.
• Avoid harmful drugs: We should avoid taking harmful drugs and alcohol.

Ans. The swelling on the neck of Radha may be because of insufficient production of thyroxine which results in goitre. However slight protrusion in John’s throat may be due to enlargement of voice box, also known as Adam’s apple, in adolescent boys.

Ans.

• Regular face wash keeps the face clean and dry and helps to reduce the pimples.
• During adolescence, secretion of sweat glands and sebaceous glands increases leading to formation of acne and pimples.
• During adolescence, all parts of the body do not grow at the same rate. Sometimes the arms and legs or hands and feet of adolescents look oversized and out of proportion with the body.
• We must be self-aware, must take proper care and diet during the growing period, not get worried or lose our self-esteem.

Ans. Our law does not permit the marriages of girls below 18 years of age and the boys below 21 years.
Biologically also, it is not good for both boys and girls. Early marriages are not good for the couple due , to following reasons:

• Girls below the age of 18 are not biologically mature enough to produce a baby.
• Boys also are not mature enough to take such a major responsibility to look after their child properly and it creates many hurdles in the socio-economic development, education, maintaining livelihood, etc., of both the boys and girls. .
• The newly born babies also have to suffer many problems regarding their proper care, etc.