SCIENCE CH- THE TEEN YEARS NOTES
THE TEEN YEARS
Facts that Matter
• Adolescence: The period of life, when the body
undergoes changes, leading to reproductive maturity is known as adolescence.
• Generally,
adolescence begins at the age of 11 and lasts upto 18 or 19 years of age.
Adolescents are also called teenagers because they cover the period of the �teens� i.e. 13 to 18 or 19 years of age.
• Puberty: The period of adolescence during which a adolescent
reaches sexual maturity and becomes able to have children.
• Changes
at Puberty
• During
puberty sudden increase in height takes place. This happens due to elongation
of long bones of legs and arms that make a person tall.
• Girls
grow faster than boys by about 18 years of age, both reach their maximum
height. The rate of growth in height varies in different individual.
Height
of an individual (male or female) depends on the genes inherited from parents.
However, right kind of food during growing years is also essential.
• Calculation
for full height (cm): The average rate of growth in the height of boys and
girls with age given in the chart helps in calculating full height of the
individuals.
Calculation for full
height (cm)
For example: A girl is
9 years old and 120 cm tall. At the end of the growth period she is likely to
be
• Boys
develop larger voice boxes (Larynx) to form a protruding part of throat called
Adam�s Apple. Boys have deep voice.
In
Girls, larynx is hardly visible (Adam�s apple not visible).
They have pitched voice.
• Change in Body Shape: In boys, at the age of puberty,
shoulders generally brooden as a result of growth. In boys, the muscles of the
body grow prominently than in the girls.
In
girls, the region below the waist becomes wider. The muscles also comparatively
grow less.
Fig. 10.1 Adam�s apple in grown up boy.
• The
secretion of sweat glands and sebaceous glands (oil glands) increases during
puberty.
• Development of Sex Organs: In males, testes and penis develop completely.
Tests start producing sperms.
In
girls, ovaries enlarge and eggs begin to mature. Ovaries start releasing mature
eggs (ova).
• At
puberty, individuals reach mental, intellectual and emotional maturity.
• Secondary Sexual Character: Such as development of breasts in girls,
moustaches and beard in boys, begin to develop. These characters that help in
distinguishing the males from the females are called secondary sexual
characters.
Boys
also develop hair on their chest.
• Hormones: Hormones are chemical substances secreted in endocrine
glands. They also known as ductless glands. These glands release hormones
directly into the blood stream to reach a particular body part known as target
site.
Hormones control
the changes that occur at adolescence. The male hormone called testosterone is
secreted by the testes at the onset of puberty and cause development of facial
hair, chest hair etc. At the onset of puberty in girls, ovaries secrete female
hormone or estrogen which makes the breast develop. Their secretion is under
the pituitary endocrine gland.
• Reproductive
phase lasts for a much longer time in males than in females.
• The
uterine wall in females prepares itself to receive the developing fertilised
egg. In case there is no fertilisation, the thickened lining of the uterine
wall breaks down and goes out alongwith blood.
This
bleeding in women is called menstruation which occurs once in about 28 to 30
days.
• Menarche: The first menstrual flow which begins at puberty is known
as menarche.
• Menopause: At 45 to 50 years of age, the menstruation cycle stops.
Stoppage of menstruation is known as menopause.
• Sex chromosome: The thread structures present inside the
nucleus of every cell are called chromosomes. All human beings have 23 pairs of
chromosomes in nuceli of their cells. Two chromosomes out of these are the sex
chromosomes known as X and Y. A female has two X chromosomes whereas a male has
one X and one Y choromosomes.
• Sex
of the unborn child depends on whether the zygote has XX or XY chromosome.
Fig. 10.2 Sex determination in humans.
• Hormones other than Sex Harmones
• Metamorphosis: The change from larva to adult is called
metamorphosis. In insects, metamorphosis is controlled by insect hormones. In
frog, metamorphosis from tadpole to adult frog is controlled by thyroxine
hormone which is produced by thyroid gland. Thyroxine production requires the
presence of iodine in water.
Fig. 10.3 Position of endocrine glands in the human body.
• Nutritional need of the Adolescents: Adolescence is a stage of rapid growth
and development.
Hence,
the balanced diet is very important at this stage. Here, balanced diet means
that the meals should include proteins, carbohydrates, fats, minerals and
vitamins in requisite proportion.
• Personal Hygine:
(a)
It is more necessary for teenagers because the increased activity of sweat
glands makes the body smelly. So, daily bath is necessary.
(b)
If all body parts are not washed or cleaned everyday, the chances of bacterial
infection are more.
(c)
Girls should take special care of cleanliness during the time of menstrual
flow.
• Say �No� to Drugs: Adolescence period is full of much activities, confusion
or insecurity. Some people take advantage of this and lead adolescents to had
habits. They are addictive, and sexual contact with persons infected with HIV
may happen.
You
should be firm to say NO to such activities because they run in your health and
happiness.
Reaching the Age of
Adolescence
Multiple choice Questions
Multiple choice Questions
1. Larynx is
called
a.
Voice box
b.
Music box
c.
Respiratory organ
d.
None of these
2. The egg is
a.
Egg gamete
b.
Female gamete
c.
Both of these
d.
None of these
3. Thyroxin
produced by
a.
Pituitary gland
b.
Adrenal gland
c.
Thyroid gland
d.
Testes
4. There
are__ __ pairs of chromosome in human cell.
a.
23
b.
46
c.
22
d.
All are wrong
5. Initially
girls grow _____ than boys.
a.
Faster
b.
Slower
c.
Both of these
d.
None of these
6. The period
of maturity of reproductive organs is called.
a.
Adolescene period
b.
Mensuration
c.
Gestation period
d.
None of these
7. Fertilisation
is called
a.
To produce sperm
b.
To produce eggs
c.
Fusion of sperms and eggs
d.
All of these
8. Puberty
age in females is
a.
10-12
b.
12-14
c.
8-10
d.
More than 14 years
9. The number
of chromosomes are present in human cell.
a.
22 pairs
b.
23 pairs
c.
24 parirs
d.
26 pairs
10. The male
hormone is
a.
Estragon
b.
Projestrone
c.
Testosterone
d.
All of these
ANSWERS
1. A
2. B
3. C
4. A
5. A
6. A
7. C
8. A
9. B
10. C
Sample paper Questions
1. What is
the age of adolescence in human?
2. Which
organ is called voice box?
3. What type
of chromosomes occurs in sperms?
4. Name the
disease caused by less or not secretion of thyroxin?
5. How we can
keep our healthy?
6. Why
adolescence is also called teenage?
7. Some boys
and girls have disproportionate body structure during adolescence. Why?
8. What are
the secondary sexual characters in girls?
9. Explain
term menstruation.
10. How do
hormones help in the completion of life of insects and frogs?
11. Write some
myths which are not facts.
12. Insulin is
produced by which gland?
HOTS
1. When do noticeable changes begin in human in
adolescence?
2. Do both girls and boys grow on same rate?
3. Name female hormone.
4. What is menopause?
5. What are chromosomes?
6. What is the name of hormone produced by pancreas?
7. Which endocrine gland produces the growth hormone?
8. What do you mean by metamorphosis?
9. What is the most important change marked by puberty?
10. Explain the development of sex organs in men and
female.
11. What happens when egg gets fertilized?
12. Name the virus that causes AIDS. What are the medium
through which this virus is transmitted?
13. Explain the sex determination of a baby in human.
14. What do you understand by Adam�s apple?
Q.1. What is
the term used for secretions of endocrine glands responsible for changes taking
place in the body?
Ans. Hormones.
Q.2. Define
adolescence.
Ans. The
period of life, when the body undergoes changes, leading to reproductive
maturity is called adolescence.
Q.3. What is
menstruation? Explain.
Ans. When
the egg produced by ovary does not get fertilised, the released egg and the
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.
Q.4. List the
changes in the by that take place at puberty.
Ans. The
changes in the body of puberty are:
(i)
Sudden increase in height.
(ii)
The bones of arms and legs elongate and make a person tall.
(iii)
Growing of hair at different parts of body.
(iv)
The voice of a boy gets hoarsed.
(v)
Development of sex organs.
(vi)Growth
of moustaches and beards in the boys.
(vii)
The breast in girls develops and hips become wider whereas in boys shoulders
generally broaden.
Q.5. Prepare a
table having two columns depicting names of endocrine glands and hormones
secreted by them.
Q.6. What are
sex hormones? Why are they named so? State their functions.
Ans. The
hormones which help and control the formation of secondary sexual characters
are called sex hormones. They are called sex hormones because they control the
sexual activities and help us to distinguish boys from girls.
The
sex hormones help to delop the secondary sexual characters. Such as, in boys
they control formation of sperms by testes and growth of facial hair. In girls
they help to develop breasts, milk secreting glands or mammary glands.
Q.7. Choose the
correct option.
(a)
Adolescence should be careful about what they eat, because:
(i)
proper diet develops thcir brains.
(ii)
proper diet is needed for the rapid growth taking place in their body.
(iii)
adolescents feel hungry all the time.
(iv)
testes buds are well deloped in teenagers.
(b)
Reproductive age in women starts when their:
(i)
menstruation starts.
(ii)
breasts start developing.
(iii)
body weight increasing.
(iv)
height increases.
(c)
The right meal for adolescents consists of:
(i)
chips, noodles, cake.
(ii)
chapati, dal, vegetable.
(iii)
rice, noodles and burger.
(iv)
vegetable cutlets, chips and lemon drink.
Ans. (a)
(ii) proper diet is needed for the rapid growth taking place in their body.
(b)
(i) menstruation starts.
(c)
(ii) chapati, dal, vegetable.
Q.8. Write
notes on:
(a)
Adam's apple
(b) Secondary Sexual
characters
(c)
Sex determination in unborn baby.
Ans. (a)
Adam's apple: The protruding part in the throat is called Adam's apple. It is
the enlarged voice box or larynx. It makes the voice of boys coarse.
(b)
Secondary sexual characters: The characters which help to distinguish the male
from female are called secondary sexual characters. The characters like hair on
chest under arms, development of breast, beard and moustaches are called
secondary sexual characters.
(c)
Sex determination in unborn baby: The sex of unborn baby is determined by the
sex chromosomes. An unfertilized egg always has X chromosomes. Sperms are of
two types. One contains X chromosomes and the other contains Y chromosomes. If
sperm contributes a Y chromosome to the egg at fertilisation, the zygote would
develope into male child. If a sperm containing X chromosome fertilises the
egg, the zygote would develop into a female.
Q.9. Word game:
Use the clues to work out the words.
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
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.
Ans.
Q.10. The table
below shows the data on likely heights of boys and girls as they grow in age.
Draw graphs of height and age for both boys and girls on the same graph paper.
What conclusions can be drawn from these graphs?
Ans. We
conclude that intially, girls grow faster than boys but by about 18 years of
age both reach about their maximum height. The rate of growth in height varies
in different individuals.