Lakhmir Singh & Manjit Kaur: Reaching The Age Adolescence- 4 | Lakhmir Singh & Manjit Kaur Solutions: Class 8 Science PDF Download

Q.91. (a) What changes take place in boys during puberty?
(b) What changes take place in girls during puberty?

(a) Changes take place in boys during puberty:

(i) The most conspicuous change (clear visible change) in boys during puberty is the sudden increase in height.

(ii) Shoulder become broad and chest become wide.

(iii) Muscles of the body grow more prominently than in the girls.

(iv) Voice deepens in boys. It becomes low pitched voice.

(v) Many adolescent boys and girls may get acne and pimples on the face during puberty due to the increased activity of sebaceous glands and sweat glands in the skin.

(vi) Hair grow on the face in the form of moustache and beard, and on the chest.

(vii) Hair grows under the arms and in the region above the thighs or the pubic region.

(viii) Testes and penis become larger.

(ix) Testes start to make sperm.

(b) Changes which occur in girls during puberty are:

(i) Rapid increase in height.

(ii) The region below the waist becomes wider.

(iii) Hair grow in armpits and in pubic regions between the thighs.

(iv) The ovary enlarges and starts producing matured eggs.

(v) Menstruation begins.

(vi) Have high pitched voice.

(vii) Development and enlargement of breast.

Q.92. (a) What is meant by the ‘primary sexual characteristics’ in humans? State two primary sexual characteristics in boys and two in girls.
(b) What is meant by ‘secondary sexual characteristics’ in humans? Explain with the help of two examples.

(a) Sexual characteristics which are present in babies at birth are called primary sexual characters. They include internal and external sex organs which are present in babies at the time of their birth. The primary sexual characteristics in males are Testes and penis.
The primary sexual characteristics in females are ovaries and uterus.
(b) Sexual characteristics which develop in mature boys and girls are called secondary sexual characters. These changes are controlled by hormones.

Hormones released by the reproductive organs like testes and ovaries and involved in the development of secondary sexual characteristics are called sex hormones. The two common sex hormones are testosterone and estrogen.

Secondary sexual characteristics in males are:

• Hair grow on the face in the form of moustache and beard, and on the chest.
• Testis grow and starts producing sperms in males.

Secondary sexual characteristics in females are:

• Milk secreting glands or mammary glands develop inside the breasts.
• Initiation of menstruation.
• Ovary enlarges and starts producing matured eggs.

Q.93. Describe menstrual cycle. What is the duration of menstruation cycle in women?

• Menstrual cycle begins when a girl reaches the age of puberty. At this age, ovaries release sex hormones in the blood which cause maturation of ova in ovaries. One mature egg or ovum is released by one of the ovaries once in about 28 to 30 days. This is termed as ovulation. Before ovulation, uterus prepares itself to receive the fertilized egg. The inner lining of the uterus becomes thick and soft with lots of blood capillaries in it.
• If the ovum does not get fertilized, then the inner lining of uterus is not required and hence it breaks down and comes out through the vagina in the form of a bleeding called menstruation.
• Menstruation occurs once in about 28 to 30 days and it usually lasts for 3 to 5 days.

  
  

Q.94. (a) What is an exocrine gland? Name two exocrine glands.
(b) What is an endocrine gland? Name two endocrine glands.

(a) A gland which secretes its product into a duct or tube is called exocrine gland. Salivary gland and sweat gland are examples of exocrine glands.

(b) Endocrine glands are also known as ductless glands as they release their secretion directly into the bloodstream. Thyroid gland, adrenal gland and pituitary gland are endocrine glands.

Q.95. (a) What is meant by ‘reproductive health’?
(b) State the conditions necessary to maintain good reproductive health during adolescence.

(a) Reproductive health is defined as a state of physical, mental and social well- being of a person in all matters relating to the reproductive system at all stages of life.

(b) The important conditions necessary to maintain good reproductive health during adolescence are:

• It is necessary to eat balanced diet during adolescence.
• It is necessary to maintain personal hygiene during adolescence.
• It is necessary to take adequate physical exercise during adolescence.
• It is necessary to avoid taking any drugs during adolescence.

Q.96. Reproductive age in women starts when their:
(a) Menstruation starts
(b) Breasts start developing
(c) Body weight increases
(d) Height increases

Correct Answer is option (a)
In females, the reproductive phase of life begins at puberty (10 to 12 years of age) and generally lasts till the age of approximately 45 to 50 years. The first occurrence of menstruation at puberty is called menarche. It is the beginning of the reproductive life of a girl.

Q.97. The sex of a child is determined by:
(a) The presence of an X chromosomes in egg (or ovum)
(b) The presence of a Y chromosomes in sperm
(c) The egg of father and mother
(d) The length of the mother’s pregnancy

Correct Answer is option (b)
The sex of a child is determined by the presence of a Y chromosomes in sperm.

Q.98. The legal age for the marriage of boys in our country is:
(a) 16 years
(b) 18 years
(c) 21 years
(d) 24 years

Correct Answer is option (c)
The legal age for the marriage is 21 years for boys, and 18 years for girls in our country.

Q.99. The legal age for the marriage of girls in our country is:
(a) 16 years
(b) 18 years
(c) 21 years
(d) 24 years

Correct Answer is option (b)
The legal age for the marriage is 21 years for boys, and 18 years for girls in our country.

Q.100. The right meal for adolescents consists of:
(a) Chips, noodles, coke
(b) Chapati, dal, vegetables
(c) Rice, noodles and burger
(d) Vegetable cutlets, chips and lemon drink

Correct Answer is option (b)
Adolescents need balanced diet for normal growth and development of the body. A balanced diet means that the meals include proteins, carbohydrates, fats and vitamins in requisite proportions. Our Indian meal of roti /rice, dal(pulses) and vegetables is a balanced meal.

Q.101. Adolescents should be careful about what they eat because Adolescents should be careful about what they eat because:
(a) Proper diet develops their brains
(b) Proper diet is needed for the rapid growth taking place in their body
(c) Adolescents feel hungry all the time
(d) Taste buds are well developed in teenagers

Correct Answer is option (b)

Adolescents should be careful about what they eat because proper diet is needed for the rapid growth taking place in their body.

Q.102. AIDS disease is caused by:
(a) Bacteria
(b) Virus
(c) Worms
(d) Protozoa

Correct Answer is option (b)

AIDS is caused by a dangerous virus called HIV. This virus can be spread from infected person to healthy person by sharing the syringes used for injecting drugs.

Q.103. Which of the following human disease can be prevented by the same hormone which brings about metamorphosis in frogs?
(a) Diabetes
(b) Anaemia
(c) Goiter
(d) Reckets

Correct Answer is option (c)
Thyroxine hormone is required for the metamorphosis of larvae (tadpoles) into adult frogs. Iodine is needed continuously by thyroid gland to make thyroxine hormone. If people do not have enough iodine in their die, they will get goiter disease caused by lack of thyroxine. So, people are advised to use iodized salt in cooking food.

Q.104. Which of the following is a mis-matched pair?
(a) Adrenaline : pituitary gland
(b) Estrogen : ovary
(c) Pancreas : insulin
(d) Testosterone : testis

Correct Answer is option (a)
Adrenaline hormone secreted by adrenal glands whereas pituitary gland secretes growth hormone.

Q.105. The hormone which is associated with male puberty is called:
(a) Oestrogen
(b) Adrenaline
(c) Testosterone
(d) Progesterone

Correct Answer is option (c)
Testosterone is a male sex hormone which is secreted by testes. This hormone brings changes in boys such as growth of facial hair.

Q.106. The dramatic changes in body features associated with puberty are mainly because of the secretions of:
(i) Thyroxine
(ii) Estrogen
(iii) Adrenaline
(iv) Testosterone
(a) A and B
(b) B and C
(c) A and C
(d) B and D

Correct Answer is option (d)
Estrogen and testosterone are sex hormones which involved in the development and control of the reproductive organs and secondary sexual characteristics.

Q.107. Which of the following endocrine gland does not occur as a pair in the human body?
(a) Adrenal
(b) Pituitary
(c) Testis
(d) Ovary

Correct Answer is option (b)
Pituitary gland is attached to the base of brain. It secretes growth hormone.

Q.108. Iodine is necessary for the synthesis of one of the following hormones. This hormone is:
(a) Adrenaline
(b) Auxine
(c) Insulin
(d) Thyroxine

Correct Answer is option (d)
Iodine is needed continuously by thyroid gland to make thyroxine hormone. If people do not have enough iodine in their die, they will get goiter disease caused by lack of thyroxine. So, people are advised to use iodized salt in cooking food.

Q.109. Which of the following endocrine gland does not a primary sexual characteristic in females?
(a) Fallopian tubes
(b) Ovaries
(c) Seminal vesicles
(d) Vagina

Correct Answer is option (c)
Ovaries, vagina and fallopian tubes are organs of female reproductive system whereas seminal vesicles are part of male reproductive system.

Q.110. Which of the following is the secondary sexual characteristics in females?
(a) Low pitched voice
(b) Broadening of chest
(c) Broadening of hip
(d) Developing Adam’s apple

Correct Answer is option (b)
During puberty, the region below the waist becomes wider in girls.

Q.111. Which of the following can lead to menstruation in a 21 year old woman during ovulation?
(i) Sperms available for fertilization
(ii) Oviducts blocked
(iii) Sperms not available for fertilization
(iv) Oviducts not blocked
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (i) and (iii)
(d) (ii) and (iv)

Correct Answer is option (b)
There are two conditions which can lead to menstruation in a 21-year-old woman during ovulation. These are: (i) Blocked oviduct and, (ii) sperms not available for fertilization.

Q.112. The faulty functioning of an endocrine gland can make a person very short or very tall.
This gland is:
(a) Thyroid
(b)  Pituitary
(c)  Adrenal
(d)  Pancreas

Correct Answer is option (b)
Growth hormone is secreted by pituitary gland. Growth hormone is necessary for the normal growth of a person.

Q.113. Which of the following hormone prepares our body for action in emergency situations?
(a) Testosterone
(b) Insulin
(c) Thyroxine
(d) Adrenaline

Correct Answer is option (d)
Adrenaline hormone prepares our body for action to face emergency situation like danger, fear, anger or excitement.

Q.114. A doctor advised a person to take injection of insulin because:
(a) His blood pressure was high
(b) His heart beat was high
(c) His blood sugar was high
(d) His thyroxine level in blood was high

Correct Answer is option (c)
Insulin hormone is secreted by pancreas. The function of insulin hormone is to lower the blood sugar level.

Q.115. Pimples and acne are formed due to the increased activity of:
(i) Adrenal glands
(ii) Sebaceous glands
(iii) Thyroid gland
(iv) Sweat glands
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (i) and (iii)
(d) (ii) and (iv)

Correct Answer is option (d)
Many adolescent boys and girls may get acne and pimples on the face during puberty due to the increased activity of sebaceous glands and sweat glands in the skin.

Q.116. When a human female reaches a certain age, then vaginal bleeding occurs for a few days after regular intervals of time:
(a) What is this process known as (i) in scientific terms, and (ii) in everyday language?
(b) What is the human female said to have attained at this stage?
(c) What does the onset of this process in human female signify?
(d) At what particular event in the life of a human female this process stops temporarily but starts again?

(e) What name is given to the event when this process stops permanently?

(a) (i) It is known as menstruation in scientific terms.

(ii) It is known as periods in everyday language.

(b) The process of menstruation begins at Puberty.

(c) The onset of menstruation in human female signify that the reproductive system of human female has started working.

(d) In the beginning of pregnancy, the process of menstruation stops temporarily but starts again.

(e) When menstruation stops permanently, it is termed menopause.

Q.117. A woman is in her reproductive phase of life. Even when the sperms are available at the time of release of a mature ovum by her ovary, fertilization does not take place. Due to this, the woman is unable to bear a baby.
(a) What is the most likely defect in the reproductive system of this woman?
(b) Name the technique by which this woman can also have a baby?

(a) Due to blocked oviducts of the woman, the ovum released by her ovary cannot meet the sperm and get fertilized.

(b) In vitro fertilization technique is used to help those couples in having babies who can produce sperms and ovum but fertilization does not take place inside the woman’s body due to blocked oviducts.

Q.119. Raj Kumar and his wife Sunita have been blessed with a baby girl. On the other hand, Kripa Shanker and his wife Vimla have been blessed with a baby boy. What type of sex chromosome has been contributed:
(a) By raj Kumar
(b) By Sunita
(c) By Kirpa Shanker
(d) By Vimla

If X chromosome carrying sperm fuses with an egg cell carrying X chromosome at fertilization, then the zygote will have XX chromosomes and develop into a female child.

In the other case, if Y chromosome carrying sperm fuses with an egg cell carrying X chromosome at fertilization, then the zygote will have XY chromosomes and develop into a male child. Thus, father is responsible for the sex of the unborn child.

(a) Raj Kumar and his wife Sunita have been blessed with a baby girl. It means, X chromosome has been contributed by raj Kumar.

(b) Sunita also contributed X chromosome.

(c) Kripa Shanker and his wife Vimla have been blessed with a baby boy, thus, kripa shanker contributed Y chromosome.

(d) Vimla contributed X chromosome.

Q.119. A gland W is located just below the stomach in the human body. The gland W secrets a hormone X. The deficiency of hormone X in the body causes a disease Y in which the blood sugar level of a person rises too much. The person having high blood sugar is called Z. What are W, X, Y and Z?

W is Pancreas ; X is Insulin ; Y is Diabetes ; Z is Diabetic.

Q.120. It was observed that the tadpoles are not growing into adult frogs in a village pond. A scientist who was asked to find the reason for this concluded that the pond water did not contain sufficient amount of a mineral P which could make a hormone Question The hormone Q can causes a phenomenon R in tadpoles so that they become adult frogs.
(a) What are (i) P (ii) Q, and (iii) R?
(b) name one human disease which can also be caused due to the deficiency of P in the food and water.

(a)

• iodine
• Thyroxine
• Metamorphosis

(b) Iodine is needed continuously by thyroid gland to make thyroxine hormone. If people do not have enough iodine in their die, they will get goiter disease caused by lack of thyroxine. So, people are advised to use iodized salt in cooking food.