Friday, 22 March 2013

Chapter 10. Reaching The Age Of Adolescence | Science | CBSE Class VIII (8th) | Solved Exercises

Question 1. What is the term used for secretions of endocrine glands responsible for changes taking place in the body?
Answer :The secretions of endocrine glands responsible for changes taking place in the body is called hormones.Hormones are chemical substances, which are released by endocrine glands directly into the blood stream.. The changes which occur at onset of puberty and adolescence are controlled by hormones
Question 2. Define adolescence.
Answer :The period of life, when the body undergoes changes, leading to reproductive maturity, is called adolescence.Adolescence begins around the age of 11 and lasts upto 18 or 19 years of age.Since this period covers the ‘teens’ , adolescents are also called ‘teenagers’. In girls, adolescence may begin a year or two earlier than in boys. Also, the period of adolescence varies from person to person.The Adolescence is marked by the onset of puberty in which growth of the reproductive organs , change in body size, change in body height, change in Voice etc takes place.
Question 3. What is menstruation? Explain.
Answer :In females, the reproductive phase starts at onset of puberty around 10 to 12 years of age and continues till 40-45 yrears of age. During this period, One ovum 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 and prepares itself to receive the developing fertilised egg. In case there is no fertilisation, the released egg, and the thickened wall lining of the uterus along with its blood vessels, breaks down and goes out of the body. This periodic bleeding due to reproductive cycle in women which is called menstruation.
Question 4. List changes in the body that take place at puberty.
Answer :List changes in the body that take place at puberty.
  1. Increase in Height - The most visible change during puberty is the sudden increase in body height.
  2. Change in Body Shape - The onset of puperty is marked by characteristic changes in body shape.In boys, the shoulders of boys generally broaden . In girls,the region below the waist becomes wider. In boys, the muscles of the body grow more prominently than in the girls.Thus, changes occurring in adolescent boys and girls are different.
  3. Voice Change - At puberty, the voice box or the larynx begins to grow.Boys develop larger voice boxes than girls, resulting in Generally, girls have a high pitched voice, whereas boys have a deep voice..
  4. Increased Activity of Sweat and Sebaceous Glands- 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.
  5. 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.During this period change in Secondary Sexual Characters results in development of breasts in girls and apperance of facial hair (moustache and beard) boys.
  6. Reaching Mental, Intellectual and Emotional Maturity - The puberty is marked by Adolescence stage, in which a person becomes more thoughtful, concious and independent than before
Question 5. Prepare a Table having two columns depicting names of endocrine glands and hormones secreted by them.
Answer :

Names of Endocrine GlandsType of hormones secretions
Pituitary glandGrowth Hormone & Hormone Stimutors
Pancreas Insulin
ThyroidThyroxine
AdrenalsAdrenalin
TestesTestosterone
ovariesEstrogen, 
Question 6. What are sex hormones? Why are they named so? State their function.
Answer :-The sex hormones are also known as male hormone (testosterone) and female hormone (estrogen). These are sereted by testes and ovaries in male and female respectively. These hormones are responsible for the male and female secondary sexual characters. Further, the sex hormones, under the control of hormones from the pituitary gland,secrete many hormones, one of which makes ova mature in the ovaries and sperms form in the testes
Question 7. Choose the correct option.
  1. Adolescents should be careful about what they eat, because
    1. proper diet develops their brains.
    2. proper diet is needed for the rapid growth taking place in their body.
    3. adolescents feel hungry all the time.
    4. taste buds are well developed in teenagers.
  2. Reproductive age in women starts when their
    1. menstruation starts.
    2. breasts start developing.
    3. body weight increases.
    4. height increases.
  3. The right meal for adolescents consists of
    1. chips, noodles, coke
    2. chapati, dal, vegetables.
    3. rice, noodles and burger.
    4. vegetable cutlets, chips and lemon drink.
Answer :
  1. Adolescents should be careful about what they eat, because - (ii) Proper diet is needed for the rapid growth taking place in their body.
  2. Reproductive age in women starts when their - (i) menstruation starts
  3. The right meal for adolescents consists of -(ii) chapati, dal, vegetables.
Question Write notes on—
  1. Adam’s apple.
  2. Secondary sexual characters.
  3. Sex determination in the unborn baby.
Answer :-


  1. Adam’s apple : At puberty, the voice box or the larynx begins to grow. Boys develop larger voice boxes than girls. Due to this, Generally, girls have a high pitched voice, whereas boys have a deep voice. The growing voice box in boys, which is visible as a protruding part of the throat, is called Adam’s apple.
  2. Secondary sexual characters : During onset of puberty in human beings, apart from the growth of reproductive organs such as testes and ovaries in males and females, There are other apparent visible changes, which are distinct in male and females and can be noticed on seeing. In girls, breasts begin to develop at puberty and boys begin to grow facial hair, as moustaches and beard. All these features, which help in to distinguish the male from the female , are called secondary sexual characters.
  3. Sex determination in the unborn baby :The thread like structures, chromosomes, present inside a fertilised egg or zygote are the embedded instruction for determining the sex of the baby. 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. 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.
Question 8. Word game : Use the clues to work out the words.
  1. Across
    • 3. Protruding voice box in boys
    • 4. Glands without ducts
    • 7. Endocrine gland attached to brain
    • 8. Secretion of endocrine glands
    • 9. Pancreatic hormone
    • 10. Female hormone
  2. Down
    • 1. Male hormone
    • 2. Secretes thyroxine
    • 3. Another term for teenage
    • 5. Hormone reaches here through blood stream
    • 6. Voice box
    • 7. Term for changes at adolescence
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Answer :-
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---------3ADAMSAP PLE

---
---------D------ --------
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---------4ENDOCRI NE------
---------S------ ------5T-
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------A--E-----7PITUITARY
----8HORMON-----U------G-
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9INSULIN

10EST-ROGE N-----T-
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Question 10. The table below shows the data on likely heights of boys and girls as they grow in age. Draw graphs showing height and age for both boys and girls on the same graph paper. What conclusions can be drawn from these graphs?

Answer :-
  1. At the time of birth the height of the boys and Girls are identical
  2. From the time of birth, till the age of 8 years, The height of boys grow sligtly more than girls.
  3. After the age of 8 years, the height of girls outpaces the height of boys till the age of 12 years.
  4. After age of 12 years, the height of boys increases at slightly faster rate and becomes almost equal to that of girls at 16th year
  5. After 16th year, the boys continued to grow more in height till the age of 20 years

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