CBSE Class 8 Science Reaching The Age Of Adolescence Notes

CBSE Class 8 Science Reaching the Age of Adolescence Chapter Notes. Learning the important concepts is very important for every student to get better marks in examinations. The concepts should be clear which will help in faster learning. The attached concepts made as per NCERT and CBSE pattern will help the student to understand the chapter and score better marks in the examinations.

REACHING THE AGE OF ADOLESCENCE

ADOLESCENCE

• The period of life, when the our body undergoes changes, leading to reproductive maturity, is called adolescence.
                     O R
• The period of transition from childhood to adulthood is called adolescence.

• Adolescence begins around the age of 11 and lasts upto 18 to 19 years of age.

• This period covers the 'teens' (13 to 18 or 19 years of age), adolescents are also called 'teenagers.'

PUBERTY

The start of the time when a boy is biologically ready to become a father, and a girl is biologically ready to become a mother.

REVIEW QUESTIONS

1. What is adolescence ?

2. Define puberty.

3. Adolescents are generally called teenagers. Why ?

CHANGES AT PUBERTY

Increase in Height :

• The most conspicuous change during puberty is the sudden increase in height. At this time the long bones, that is, the bones of the arms and the legs elongate and make a person tall.

• The rate of growth in height varies in different individuals.

• Height of an individual is more or less similar to that of some family member. This is because height depends on the genes inherited from parents. It is , however, very important to eat the right kind of food during these growing years. This helps the bones, muscles and other parts of the body get adequate nourishment for growth.

Change in Body Shape :

• In boys shoulders generally broaden as a result of growth.

• In girls, the region below the waist becomes wider.

• In boys, the muscles of the body grow more prominently than in the girls.

Voice Change :

• At puberty, the voice box or the larynx begins to grow. Boys develop larger voice boxes. The growing voice boxes 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.

• Generally, girls have a high pitched voice, whereas boys have a deep voice.

Increased Activity of Sweat and Sebaceous Gland :

• During puberty the secretion of sweat glands and sebaceous glands (oil glands) increases. Many young people get acne and pimples on the face at this time because of the increased activity of these glands in the skin.

Development of Sex Organs :
• At puberty, male sex organs like the testes and penis develop completely. The testes also begin to produce sperms.

• In girls, the ovaries enlarge and eggs begin to mature. Also ovaries start releasing mature eggs.

Reaching Mental, Intellectual and Emotional Maturity :

Mental growth :- Thinking skill develops. They are able to think in a more flexible, abstract, and logical way. The ability to see others point of view, exploring ideas, developing concepts and memory skills improve.

Emotional growth :- Emotional changes cause the young person to look at friend and family in new ways. They are very happy at one moment and the very next their mood changes. These comes a feeling of giving and of helping people. Interest in the opposite sex and desire for closeness arise.

Social growth :- In includes developing a personal identity, accepting oneself, forming more mature relationships with peers of both sexes, developing independence and preparing for a career.

REVIEW QUESTIONS

1. Name the male sex hormone.

2. List the changes which are occur at puberty.

3. What is Adam's apple ?

4. Name the female sex hormone.

SECONDARY SEXUAL CHARACTERS

The reproductive organs are testes and ovaries which produce the gametes, i.e., sperms in males and ova in females. The features which help to distinguish the male from the female, are called secondary sexual characters.

Pubertal Changes (Secondary Sexual Characters) in Male :

Widening of shoulders.

Deepening of voice.

Growth of hairs under chest armpits and around pubic area.

Appearance of beard and moustaches.

Growth of sex organs, [Testes & Penis].

Increased activity of sweat and sebaceous glands.

Oily skin and appearance of pimples.

Darkening in skin colour of the genital area.

Pubertal Changes (Secondary Sexual Characters) in Female :

Widening of pelvis and hips.

High pitch voice.

Growth of hairs under armpits and around pubic area.

Initiation of menstrual cycle.

Growth of mammary glands (breasts).

Maturation of secondary sex organs like fallopian tubes, uterus.

Increased activity of sweat and sebaceous glands.

Oily skin and appearance of pimples.

Darkening in skin colour of the genital area.

REVIEW QUESTIONS

1. Define secondary sexual characters.

2. Write the secondary sexual characters in boys.

3. Write the secondary sexual characters in girls.

4. Which endocrine gland stimulates testes and ovaries to release sex hormones ?

Reproductive Phase of Life in Humans:-

Adolescents become capable of reproduction when their testes and ovaries begin to produce gametes. The capacity for maturation and production of gametes lasts for a much longer time in males than in females. 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.

Menstruation occurs once in about 28 to 30 days.

The first menstrual flow begins at puberty and is termed menarche.

At 45 to 50 years of age, the menstrual cycle stops. Stoppage of menstruation is termed menopause.

Menstrual cycle is controlled by hormones. The cycle includes the maturation of the egg, its release, thickening of uterine wall and its breakdown if pregnancy does not occur. In case the egg is fertilised it begins to divide and then gets embedded in the uterus for further development.

SEX DETERMINATION

All human beings have 23 pairs of chromosomes in the nuclei of their cells. Two chromosomes out of these are the sex chromosomes, named X and Y.

A female has two X chromosomes, while a male has one X and one Y chromosome. The gametes (egg and sperm) 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 the other kind has a Y chromosome.

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. The sex chromosomes of the father determine the sex of an unborn baby. The belief that the mother is responsible for the sex of her baby is completely wrong and to blame her for this is totally unjustified.

REVIEW QUESTIONS

1. How many chromosomes are present in human beings ?

2. Define the term menarche ?

3. Which hormone play main role in menstrual cycle ?

4. What is number of sex chromosomes in human male and female ?

5. Who is the responsible to determine the sex of unborn baby ?

Role of Hormones in Completing the Life History of Insects and Frogs :-

The caterpillar of silk worm has to pass through various stages to become an adult. Similarly, a tadpole also passes through various stages to become a frog.

This process of change from larvae or caterpillar to an adult is called metamorphosis. The process of metamorphosis in insects is controlled by insect hormones.

In a frog the process of metamorphosis is regulated by thyroxine hormone which is produced by thyroid gland. A tadpole cannot become an adult if there is deficiency of iodine in the water where it is growing.

REPRODUCTIVE HEALTH

Health is a state of complete mental, physical and social well being.

• Nutritional Needs of the Adolescents :-

♦ 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.

♦ Milk is a balanced food in itself.

♦ Fruits also provide nourishment.

♦ For infants, mother's milk provides all the nourishment that they need.

♦ Iron builds blood and iron-rich food such as leafy vegetables, jaggery, meat, citrus, Indian gooseberry (amla) are good for adolescents.

♦ Chips and packed or tinned snacks, through very tasty should never replace regular meals as they do not have adequate nutritional value.

• Personal Hygiene :-

Everyone should have a bath at least once everyday. It is more necessary for teenagers because the increased activity of sweat glands sometimes makes the body smelly. All parts of the body should be washed and cleaned everyday. If cleanliness is not maintained there are chances of catching bacterial infection. Girls should take special care of cleanliness during the time of menstrual cycle.

• Physical exercise :-

Walking and playing in fresh air keeps the body fit and healthy. All young boys and girls should take walks, exercise and play outdoor games.

• Say "NO" to Drugs and Alcohols :-

Adolescence is a period of much activity in the body and mind which is a normal part of growing up. So do not feel confused or insecure. If anybody suggests that you will get relief if you take some drugs, just say 'No' unless prescribed by the doctor. Drugs are addictive. If you take them once, you feel like taking them again and again. They harm the body in the long run. They ruin health and happiness.

REVIEW QUESTIONS

1. Define 'balanced diet.'

2. Why physical exercise is essential for adolescents ?

3. How can you achieve a healthy life ?

4. Define metamorphosis.

ADOLESCENT PREGNANCY

You might be knowing that in our country, the legal age for marriage is 18 years for girls and 21 years for boys. This is because teenage mothers are not prepared mentally or physically for motherhood. Early marriage and motherhood cause health problems in the mother and the child. It also curtails employment opportunities for the young woman and may cause mental agony as she is not ready for responsibilities of motherhood.

AIDS (ACQUIRED IMMUNO DEFICIENCY SYNDROME)

AIDS is a disease which is caused by HIV virus. This virus destroys the natural defence mechanism of the body and makes it susceptible to diseases.

Causes of AIDS

1. Sharing the needle of the syringe for injecting drugs.

2. Unprotected sex with an infected person.

3. Transfusing blood into the body of a healthy person from an infected person.

4. Infected mother can pass HIV virus through milk to an infant.

How to Prevent AIDS

1. Use disposable syringes.

2. Get blood from registered blood banks for transfusion.

3. Have safe and protected sex.

4. HIV infected mother should not breast feed her baby

5. Be faithful to your partner.

HUMAN ENDOCRINE SYSTEM
• The branch of biology which deals with study of endocrine system and its physiology is known as "endocrinology".
• "Thomas Addison" is known as 'Father of Endocrinology'.
• The glands which pour their secretion directly in the blood are called endocrine glands. These glands lack ducts, so these glands are called ductless glands. e.g.– Thyroid gland, parathyroid gland.
• Whereas the glands with duct are called exocrine glands. e.g. – Sweat gland, salivary gland.
• Pancreas has both exocrine and endocrine part, so it is also called mixed gland or common gland or heterocrine gland.

H O R M O N E S 
• Substances secreted by endocrine glands are called "Hormones".
• The term hormone was coined by Starling.         

1. What are hormones?
2. What are endocrine glands?
3. What are the secretions of endocrine glands known as?
4. Distinguish between exocrine and endocrine glands.
5. Term "Hormone" was coined by ? 

OBJECTIVE QUESTIONS

Question. A hormone secreted in a female body only :-
(A) Progesterone
(B) Testosterone
(C) Thyroxine
(D) Adrenalin
Answer: A

Question. Sexual maturity in males obtained at the age of :-
(A) 12-13 years
(B) 13-14 years
(C) 14-15 years
(D) 16-17 years
Answer: C

Question. 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
Answer: B

Question. The stage when the reproductive organs reach sexual maturity is called :-
(A) puberty
(B) menstruation
(C) gestation
(D) fertilization
Answer: A

Question. Which of the following is not a part of female reproductive system ?
(A) ovary
(B) oviduct
(C) uterus
(D) embryo
Answer: D

Question. Reproductive age in women starts when their :-
(A) Menstruation starts
(B) Breasts starts developing
(C) Body weight increases
(D) Height increases
Answer: A

Question. In a frog the process of metamorphosis is regulated by :-
(A) Insulin
(B) Testosterone
(C) Growth hormone
(D) Thyroxine
Answer: D

Question. Sperms in male are produced in :-
(A) testes
(B) urethra
(C) epididymis
(D) penis
Answer: A

Question. Which of the following constitutes the right meal for adolescents ?
(A) Chips, noodles, coke
(B) Chapatti, dal, vegetables
(C) Rice, noodles and burger
(D) vegetable cutlets, chips and lemon drink
Answer: B

Question. After fertilization the human embryo grows inside the :-
(A) uterus
(B) ovary
(C) fallopian tubes
(D) zygote
Answer: A

Question. Secretions of endocrine glands are called :-
(A) enzymes
(B) hormones
(C) catalysts
(D) sugars
Answer: B

Question. The features which help to distinguish the male from the female are called :-
(A) Sex chromosomes
(B) Primary sexual characters
(C) Secondary sexual characters
(D) All of these
Answer: C

Question. If fertilization doesn't occur, the ovum is released out of :-
(A) urine
(B) menstrual cycle
(C) sweat
(D) None of these
Answer: B

Question. The fusion of male and female gametes usually takes place inside the :-
(A) uterus
(B) ovary
(C) fallopian tubes
(D) zygote
Answer: C

Question. The process of release of ovum by the respective ovary is called as :-
(A) Ovulation
(B) Menstruation
(C) Menarche
(D) Menopause
Answer: A

FILL IN THE BLANKS

Question. The sex chromosomes of ................. determine the sex of an unborn baby. 
Answer: Male

Question. ................. maintains the level of sugar in the blood.
Answer: Insulin

Question. The sex chromosomes are designated as ................. and ................. .
Answer: X, Y

Question. ................. causes pimples in both boys and girls at puberty.
Answer: Hormones

Question. Generally girls have a ................. voice, whereas the voice in boys is ................. .
Answer: High pitched, low pitched

Question. Thyroid gland produces ................. hormone.
Answer: Thyroxine

Question. Endocrine glands release hormones directly into the ................. .
Answer: Blood

Question. Testes produce male sex hormone ................. .
Answer: Testosterone

Question. Menstrual cycle is controlled by mainly ................. hormone.
Answer: Estrogen

Question. ................. is also called the emergency hormone.
Answer: Adrenaline

WRITE TRUE OR FALSE FOR THE FOLLOWING

Question. Mother is responsible for the sex of a baby.
Answer: F

Question. The first menstrual flow begins at puberty and is termed menopause.
Answer: F

Question. Estrogen is a female sex hormone.
Answer: T

Question. The stoppage of menstruation is termed menarche.
Answer: F

Question. Pituitary gland is also called the master gland.
Answer: T

Question. The human body undergoes several changes during adolescence. These changes mark the onset of puberty.
Answer: T

Question. Diabetes is caused due to the deficiency of insulin in the blood.
Answer: T

Question. The height of an individual depends on the genes inherited from the parents.
Answer: T

Question. Menstrual cycle starts in a girl at puberty.
Answer: T

Question. In girls, the muscles of the body grow more prominently than in the boys.
Answer: F

MATCH THE FOLLOWING ( IMAGE PAGE NO. 9)

(A) (1) → f ; (2) → e ; (3) → d ; (4) → a ; (5) → b ; (6) → c.

Question. Endocrine glands put their secretions directly into :-
(A) ducts
(B) blood
(C) both
(D) none of these
Answer: B

Question. The first hormone to be isolated was :-
(A) thyroxine
(B) testosterone
(C) epinephrine
(D) secretin
Answer: D

Question. According to the accepted concept of hormone action, if receptor molecules are removed from target organs :-
(A) the target organ will continue to respond to the hormone without any difference
(B) the target organ will continue to respond to the hormone but will require higher concentration
(C) the target organ will not respond to the hormone
(D) the target organ will continue to respond to the hormone but in the opposite way
Answer: C

Question. In an accident the anterior pituitary of a four year old boy was severely damaged but the boy survived. What is likely to happen :-
(A) High levels of thyroxine will be released
(B) Spermatogenesis will be released
(C) The boy will not grow much in height
(D) The growth of mammary glands will be stimulated
Answer: C

Question. A gorilla like man with huge hand and legs. This is due to the abnormal secretion of :-
(A) pituitary FSH
(B) pituitary LH
(C) pituitary GH
(D) thyroid
Answer: C

Question. LH and FSH are called :-
(A) antistress hormones
(B) gonadotropic hormones
(C) emergency hormone
(D) neurohormones
Answer: B

Question. FSH is to estrogen as LH is to :-
(A) vasopressin
(B) testosterone
(C) progesterone
(D) LTH
Answer: C

Question. In a pregnant woman having prolonged labour pains, its childbirth has to be hastened. It is advisable to administer a hormone that can :-
(A) activate the smooth muscles
(B) increase the metabolic rate
(C) release glucose into the blood
(D) stimulate the ovary
Answer: A

Question. Diabetes insipidus is the syndrome which results due to the :-
(A) failure of neurohypophysial system to inhibit the excess release of ADH
(B) failure of neurohypophysial system to produce or release ADH
(C) inability of pituitary to produce oxytocin
(D) inability of pituitary to release ACTH
Answer: B

Question. If a rat was given an injection of sodium iodide with radioactive iodine, then in which one of the following most of the iodine would be incorporated ?
(A) Cartilage
(B) Thyroid
(C) Lymph nodes
(D) Parathyroid
Answer: B

Question. Failure of insulin production results in :-
(A) addison's disease
(B) cushing's disease
(C) diabetes insipidus
(D) diabetes mellitus
Answer: D

Question. The gland whose hormone affects the functions of many other endocrine glands is :-
(A) thyroid gland
(B) pituitary gland
(C) pancreas
(D) parathyroid
Answer: B

Question. Injecting a tadpole with thyroxine would lead to :-
(A) giant but normal tadpoles
(B) precocious metamorphosis
(C) stoppage of metamorphosis
(D) atrophy of gonads
Answer: B

Question. A very high level of calcium in the blood suggests malfunction of the :-
(A) parathyroid
(B) thyroid
(C) thymus
(D) adrenal gland
Answer: A

Question. Cortisone is used for the treatment of inflammation, allergy and arthritis. Which of the following endocrine glands produces cortisone :-
(A) Thyroid
(B) Pancreas
(C) Adrenal
(D) Gonads
Answer: C

Q1. what is adolescence.?

A1. It is the period of life when the body undergoes changes, leading to reproductive maturity.

Q2. Define puberty.

A2. The stage when human body becomes sexually mature.

Q3. Enlist the changes occurring in males and females during puberty.

Q4. What is adam’s apple?

A4. The growing voice box in boys can be seen as a protruding part of the throat called adam’s apple.

Q5. What are secondary sexual characters?

A5. These are the features that help to distinguish males from females.

Q6. Define the following terms.

1. Hormone- they are chemical messengers for various processes and activities in the body

2. Endocrine glands- the ductless glands which secrete hormones directly into blood.

Q7. What is the role of hormones in initiating reproductive function?

A7. 1. Hormones from pituitary stimulate testes and ovaries to release testosterone and estrogen respectively.

2. These sex hormones reach to target sites via blood.

3. Then stimulate changes in the body at the onset of puberty.

Q8. Discuss reproductive phase of life in women.

A8. In females the reproductive phase of life begins at puberty and continues till they reach the age of 45-50 years. The egg begins to mature with the onset of puberty. One mature ovum is released by one of the ovaries every month. The process is called ovulation. During this period, the walls of the uterus become thick so as to receive fertilized egg. Then this egg gets implanted in the uterus resulting in pregnancy.

Q9. How is the sex of a baby determined?

A9. 

Q. Give reasons for the following :

1. Tadpoles growing in iodine deficient water have retarded growth.

A. The process of growth and development is regulated by thyroxine hormone which is produced by thyroid gland. Iodine is required for thyroxine production. That is why retarded growth is seen in tadpoles living in iodine deficient water.

2. Voice becomes hoarse in adolescent boys.

A. Sometimes the muscles of the growing voice box go out of control and the voice becomes hoarse.

3. Adolescents experience acne and pimples.

A. This is dues to increased activity of sebaceous (oil) glands in the skin.

4. Females have no role in determining gender of a child.

A. Y- chromosomes that leads to a boy offspring is contributed by male parent. That is the sperms are of two types, having either X or Y chromosome.

Q10. Name the hormone secreted by the following glands, write their functions as well.

A10 

Q11. Write short note on reproductive health of adolescents.

A11. 1. Nutritional needs of adolescents

2. personal hygiene

3. physical exercise

Q12. What are the causes of AIDS?

A12. 1. Sharing needle of the syringe

2. unprotected sex with infected person.

3. blood transfusion from infected person to healthy one.

4. infected mother can pass HIV through milk to an infant.