Cbse Class 8 Science - Chapter 10 Reaching the Age of Adolescence PPT

Class 8 Science Chapter 10
Reaching the Age of Adolescence PPT

1. REACHING THE AGE OF
ADOLESCENCE
CBSE Class 8 -Science
CHAPTER -10

2. ADOLESCENCE AND PUBERTY

3. ADOLESCENCE
•Adolescence: -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 up to 18 or 19 years of age. This is the
transitional stage from a child to an adult.

4. PUBERTY
•Puberty: -The stage of life when the body becomes capable of
reproduction is known as puberty. Puberty ends when an adolescent
reaches reproductive maturity. Puberty is normally 11-16 years in boys and
10-15 years in girls; however it may vary from person to person.

5. CHANGES AT PUBERTY

6. 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.
•All parts of the body do not grow at the same rate. For example, the arms
and legs often grow faster than other parts, making them appear oversized
and awkward. However, this is temporary and soon the body regains its
normal proportions.
•While the final height an individual attains is primarily controlled by genes,
hormones control how the height increases. It is important that the body gets
the correct nutrition during adolescence to ensure healthy growth of bones,
muscles and other parts.

7. Change in Body Shape
•In boys, the shoulders become broader and the chest becomes wider. The
muscles grow more than in girls.
•In girls, the pelvic region widens (region below the waist), hips broaden,
breasts develop and increase in size. Mammary glands (milk secretion
glands) develop inside the breasts.

8. Development of hair
•In both sexes, hair start growing in the armpits and in the pubic area (region
above the thighs). In boys, facial hair (beard and moustache) develop.

9. Voice Change
•At puberty, the voice box or the larynxbegins to grow.
•It becomes bigger in boys than in girls.
•The growing voice box in boys can be seen as a protruding part of the throat
called Adam’s apple. In girls, the larynx is hardly visible from outside because
of its small size.
•Generally, girls have a high pitched voice, while boys have a deep voice.
•In adolescent boys, as the larynx begins to grow, the voice often cracks.
•Sometimes, the muscles of the growing voice box go out of control and the
voice becomes hoarse. However, this state is temporary and the voice is
soon back to normal.

10. Increased Activity of Sweat and
Sebaceous Glands
•During puberty, there is increase in the activity of sweat and sebaceous (oil)
glands.
•This leads to increased sweating often resulting in body odour.
•The skin becomes oilier.
•This often leads to appearance of acne and pimples on the face.

11. 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.

12. Reaching Mental, Intellectual
and Emotional Maturity
•Adolescence is a period of change in a person’s way of thinking.
•Adolescents are more independent than before and are also self conscious.
•Intellectual development occurs and they tend to spend considerable time
thinking.
•It is often the time in one’s life when the brain has the greatest capacity for
learning.
•As a result of trying to adjust to the changes in the body and mind,
adolescents often find themselves feeling confused, insecure and self
conscious. This is a natural part of growing up and is experienced by
everyone. Therefore, there is no reason to feel insecure.

13. Sexual Feelings
•Sexual Maturity causes boys and girls to become interested in and attracted
to the opposite sex.

14. SECONDARY SEXUAL CHARACTERS AND
THE ROLE OF HORMONES IN INITIATING
REPRODUCTIVE FUNCTION

15. SECONDARY SEXUAL
CHARACTERS
•Testes and ovaries are the reproductive organs. They produce gametes, that
is, sperms and ova.
•The features that help to distinguish the male from the female are called
secondary sexual characters.
•In girls, breasts begin to develop at puberty.
•Boys begin to develop facial hair, that is, moustaches and beard, and chest
hair.
•In both boys and girls, hair grows under the arms and in the pubic region (the
region above the thighs).

16. Hormones
•The changes which occur at adolescence are controlled by hormones.
•Hormones are chemical substances. These are secretions from endocrine glands, or
endocrine system.
•The male hormoneor testosteronebegins to be released by the testes at the onset
of puberty. This causes changes in boys like the growth of facial hair.
•Once puberty is reached in girls, ovaries begin to produce the female hormoneor
estrogen(oestrogen) which makes the breasts develop. Milk secreting glands or
mammary glandsdevelop inside the breasts.
•The production of these hormones is under the control of another hormone secreted
from an endocrine gland called pituitary gland.
•Hormones are the chemicals the endocrine system uses to send messages to organs
and tissue throughout the body. Once released into the bloodstream, they travel to
their target organ or tissue, which has receptors that recognize and react to the
hormone.

17. Role of Hormones in Initiating
Reproductive Function
•The glands of the endocrine system are located in various parts of the body.
•Hormones generally do not act at the place where they are produced in the
body.
•They are taken by blood to specific body part, called target organs or target
site, where they act.
•The target site responds to the hormone.
•There are many endocrine glands in the body. The testes and ovaries
secrete sex hormones. These hormones are responsible for the male and
female secondary sexual characters. Further, the sex hormones are under
the control of hormones from the pituitary gland.
•The pituitary gland secretes many hormones, one of which makes ova
mature in the ovaries and sperms form in the testes.

18. The onset of puberty -controlled by hormones
Hormones from pituitary gland stimulate testes and
ovaries to release testosterone (in male) and estrogen (in
female)
Released in the blood stream and reach parts of the
body (Target site)
Stimulate changes in the body at onset of puberty

19. REPRODUCTIVE PHASE OF LIFE IN HUMANS,
MENSTRUAL CYCLE, AND
SEX DETERMINATION OF THE BABY

20. REPRODUCTIVE PHASE 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.

21. MENSTRUATION
•In females, the reproductive age starts at puberty (10-12 years of age) and
continues to approximately 45-50 years of age.
•During this period, one of the two ovaries produces an egg (or ovum) every
28-30 days. This process is called ovulation.
•During this period, the walls of the uterus become thick and cushiony to
receive the egg. This thickened lining is called endometrium.
•If the egg is fertilized, it results in pregnancy and the fertilized egg begins to
develop.
•If fertilization does not occur, the released egg, and the thickened lining of
the uterus along with its blood vessels are shed off. This causes bleeding in
women which lasts for 4-6 days and is known as menstruationor menstrual
period. Menstruation occurs once in about 28-30 days.

22. THE MENSTRUAL CYCLE,
MENARCHE AND MENOPAUSE
•The first menstrual flow begins at puberty and is known as menarche. The
periods may be irregular initially but become regular after some time.
•At around 45-50 years of age, the menstrual cycle stops and the female is no
longer reproductive. This stoppage of menstruation is known as menopause.
•The cycle of producing and maturation of the egg, its release, the thickening
of the uterine wall, and its breakdown if fertilization does not occur is known
as the menstrual cycle. The menstrual cycle is controlled by hormones.
•In case the egg is fertilized it begins to divide and then gets embedded in
the uterus for further development.

23. Determining the Sex of the Baby –
An Introduction
•Inside the fertilized egg or zygote is the instruction for determining the sex of the
baby.
•This instruction is present in the thread-like structures, called chromosomesin the
fertilized egg. Chromosomes are present inside the nucleus of every cell.
•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 unfertilized 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.

24. DETERMINING THE SEX OF THE
BABY
•When an ovum and sperm fuse, the zygote gets 23 pairs of chromosomes.
•One chromosome in each pair comes from the mother, the other from the
father.
If a sperm containing an X chromosome fertilizes the egg, the zygote would
have two X chromosomes and would develop into a female.
If a sperm containing a Y chromosome fertilizes the egg, the zygote would have
one X and one Y chromosome and would develop into a male.
•The sex chromosomes of the father determine the sex of an unborn baby.

25. Sex Determination of a
Child
Daughter
Son

26. ENDOCRINE SYSTEM

27. Endocrine System
•There are a number of slower processes that go on in the body, such as
growth. Such processes are controlled by the endocrine system.
•The endocrine system controls these processes through chemicals called
hormones.
•Hormones are secreted by a number of glands that make up the endocrine
system.
•A glandis a mass of cells in the body that produces chemical substances.
For example, pituitary gland, testes, ovaries, salivary glands that secrete
saliva. The saliva flows into the mouth through small tubes or ducts. Sweat
glands and oil glands also release their secretions through ducts.
•Glands in the endocrine system do not have ducts and release hormones
directly into the blood. Hence they are called ductless glands.

28. Pituitary Gland
•Pituitary glandis an endocrine gland.
•Thepituitary glandis located below the hypothalamus and is attached to the brain.
•It produces several hormones that control water balance, growth and also the release of
other hormones.
•The hormones it produces affect growth and reproduction. They can also control the
function of other endocrine glands.
•The growth hormone (GH) stimulates growth and development in the body.
•The thyroid stimulating hormone (TSH) stimulates the thyroid glands to produce thyroxine.
•Other hormones secreted by the pituitary stimulate testes and ovaries to produce their
hormones (testes: -testosterone, and ovaries: -oestrogen, progesterone).
•The pituitary gland is also called the master glandas it influences the functioning of the
other glands.

29. Reproductive organs –Testes and Ovaries
•Some endocrine glands also have non-endocrine functions.
•For example, the ovaries and testes produce hormones, but they also have the non-
endocrine function of producingeggsandsperm, respectively.
•The ovary in females produces the female sex hormone called oestrogen.
•The testes in males produces the male sex hormone called testosterone.
•These hormones control sexual characteristics.
Thyroid Gland
•Thethyroid glandis located in the front part of your neck. It’s very important for
metabolism.
•The thyroid gland produces a hormone called thyroxine that affects growth and
development.
•When there is a lack in thyroxine, the thyroid gland swells and causes the disease called
goitre(caused by iodine deficiency).

30. Pancreas
•Thepancreasis located in your abdomen behind your stomach.
•Its endocrine function involves controlling blood sugar levels.
•It secretes the hormone insulin, which regulates the amount of sugar in the blood.
•The pancreas has another function –it is also a part of the digestive system and secretes
the pancreatic juice.
•Diabetes is a disease caused when the pancreas does not produce the hormone insulin in
sufficient quantities.
Adrenal Glands
•Oneadrenal glandcan be found on top of each kidney.
•These glands produce hormones important for regulating functions such as blood pressure,
heart rate, and stress response.
•They secrete the hormone adrenalin when a person is angry or afraid. It helps the body to
adjust to stress when one is angry, embarrassed or worried.
•Adrenalin causes increase in heartbeat and blood pressure, and releases glucose and
other substances that provide instant energy. It thus prepares the body for the ‘fight or
flight’ reaction, that is, it prepares the body to fight or to run away from a dangerous
situation.

31. Parathyroid Gland
•Also located in the front of your neck, the parathyroid gland is important for maintaining
control of calcium levels in your bones and blood.
Hypothalamus
•While some people don’t consider it a gland, thehypothalamusproduces multiple
hormones that control the pituitary gland. It’s also involved in regulating many functions,
including sleep-wake cycles, body temperature, and appetite. It can also regulate the
function of other endocrine glands.
Pineal Gland
•Thepineal glandis found in the middle of your brain. It’s important for your sleep-wake
cycles.
Thymus
•Located in the upper torso, thethymusis active until puberty and produces hormones
important for the development of a type of white blood cell called a T cell.

32. Hormone Secreting gland(s) Function
adrenaline adrenal
increases blood pressure, heart rate, and metabolism in
reaction to stress
aldosterone adrenal controls the body’s salt and water balance
cortisol adrenal plays a role in stress response
dehydroepiandrosterone sulfate (DHEA)adrenal
aids in production of body odor and growth of body hair
during puberty
estrogen ovary
works to regulatemenstrual cycle, maintain pregnancy,
and develop female sex characteristics; aids in sperm
production
follicle stimulating hormone (FSH) pituitary controls the production of eggs and sperm
glucagon pancreas helps to increase levels of blood glucose
insulin pancreas helps to reduce your blood glucose levels
luteinizing hormone (LH) pituitary
controls estrogen and testosterone production as well as
ovulation
melatonin pituitary controls sleep and wake cycles
oxytocin pituitary helps with lactation, childbirth, and mother-child bonding
parathyroid hormone parathyroid controls calcium levels in bones and blood
progesterone ovary
helps to prepare the body for pregnancy when an egg is
fertilized
prolactin pituitary promotes breast-milk production
testosterone ovary, testes, adrenal
contributes to sex drive and body density in males and
females as well as development of male sex characteristics
thyroid hormone thyroid
help to control several body functions, including the rate of
metabolism and energy levels
Table –Endocrine Glands and the Hormones

33. Endocrine System Images

34. LIFE HISTORY OF SILK MOTH & FROG
AND METAMORPHOSIS

35. ROLE OF HORMONES IN COMPLETING THE LIFE
HISTORY OF INSECTS & FROGS -INTRODUCTION
•The life history of silk moth and frog contains various stages. The caterpillar
has to pass through various stages to become an adult moth. Similarly, the
tadpole passes through certain stages to become a frog.

36. Life History of Silk Moth

37. Life History of Frog

38. METAMORPHOSIS
•The complete change of form of an animal as it develops from a young one
into an adult is called metamorphosis.
•Metamorphosis in insects is controlled by insect hormones.
•In a frog, metamorphosis is controlled by thyroxine, the hormone produced
by thyroid.
•Thyroxine production requires the presence of iodine in water.
•If the water in which the tadpoles are growing does not contain sufficient
iodine, the tadpoles cannot become adults.

39. REPRODUCTIVE HEALTH

40. Reproductive Health
•The physical and mental well being of an individual is regarded as an
individual’s health.
•To keep the body healthy, every human being, at any age, needs to have a
balanced diet. The person must also observe personal hygiene and
undertake adequate physical exercise.
•During adolescence, however, these become even more essential as the
body is growing.

41. Nutritional Needs of
Adolescents
•Adolescence is a stage of rapid growth and
development. Hence the diet for an adolescent has
to be carefully planned.
•A balanced dietmeans that the meals include
proteins, carbohydrates, fats, vitamins and minerals in
requisite proportions.
•Our Indian meal of roti/rice, dal(pulses) and
vegetables is a balanced meal.
•Milk is a balanced food in itself.
•For Infants, mother’s milk provides all the nourishment
that they need.
•Iron builds blood and iron-rich food such as leafy
vegetables, jiggery, meat, citrus, Indian gooseberry
(amla) are good for adolescents.

42. Balanced diet
•The diet should contain adequate amounts of cereals for
carbohydrates; milk, meat, nuts, and pulses for proteins;
controlled amounts of butter/ghee/oils and sugars for energy;
and fruits and vegetables for nourishment and protection against
diseases.
•Fast food which is tasty but does not have adequate nutrition,
such as chips, packed or tinned snacks, or aerated drinks, should
not be used as substitute for meals.

43. Personal Hygiene
•Due to increased activity of sweat and sebaceous glands, proper personal
hygiene is very important for adolescents.
•Taking a bath at least once everyday and cleaning all parts of the body is
essential, otherwise body odour and bacterial infection may result.
•Girls should be especially careful about hygiene during menstrual flow. They
should keep track of their menstrual cycle and be prepared for the onset of
menstruation. Use sanitary napkin or clean homemade pads. Change pads
every 4-5 hours as per the requirement.

44. Physical Exercise
•Walking, jogging, aerobics, outdoor games, etc., are good for the growing
adolescent body.
•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.
•Discontinuing exercises to concentrate on studies is not a good practice and
can lead to health problems.

45. Always Say ‘NO’ to Drugs
•Adolescence is a period of much activity in the body and mind which is a normal
part of growing up. It is also a stage of insecurity and confusion.
•Since adolescence is a stage of insecurity and confusion, it is easy for the
adolescent mind to be led astray by wrong company or advice, and fall prey to
drug and alcohol abuse.
•If anybody suggests that you will get relief if you take some drugs, just say ‘No’
unless prescribed by the doctor.
•Drugs are very addictive and once taken, there is a tendency to take them again
and again. They harm the body in the long run, ruining health and happiness.
•When confused, confide in parents and teachers and seek their guidance, as they
are you well-wishers and have passed through the same stage. Books and good
Internet sites suggested by counsellors can also be referred.
•Seeking advice from only friends is not advisable as they themselves are
experiencing the process for the first time.

46. AIDS
•AIDS (Acquired Immune Deficiency Syndrome)
is caused by a dangerous virus, HIV.
•HIV (Human Immunodeficiency Virus infection)
virus can pass on to a normal person from an
infected person from an infected syringe by
sharing the syringes used for injecting drugs.
•It can also be transmitted to an infant from the
infected mother through her milk.
•The virus can also be transmitted through sexual
contact with a person infected with HIV.

47. Adolescent Pregnancy
•The legal age for marriage in India is 18 years for girls and 21 years for boys.
•This is because girls are not prepared physically or mentally for bearing
children or motherhood.
•Early marriage and motherhood cause health problems in the mother and
the child.
•Motherhood at such an early age also binds the young woman to the home
and stops her from having a career.

48. Myths and Taboos regarding bodily changes and Adolescents
•A girl becomes pregnant if she looks at boys during menstruation.
•The mother is responsible for the sex of her child.
•A girl should not be allowed to work in kitchen during menstruation.

49. EXERCISES

50. 1.What hormone does the adrenal glands produce? What is the function of this hormone?
2.Name four endocrine glands and the hormones they secrete.
3.What changes occur in the body shapes of boys and girls at adolescence?
4.Discuss the menstrual cycle.
5.What are hormones?
6.Why do boys have a hoarse voice at puberty?
7.What do you mean by the term ‘target site’?
8.What are the chromosomes in females and males?
9.Is mother responsible for the sex determination of the baby?
10.How many pairs of chromosomes are found in nuclei of cells of human being?
11.What is metamorphosis? Which hormones control metamorphosis in insects and frogs?
12.Why is the presence of iodine in water required for the proper growth of tadpoles?
13.What do you mean by balanced diet?
14.Define reproductive health.

51. 15.What is menarche?
16.What is menopause?
17.What are the main changes that happen at puberty? (the 6 points without explanation)
18.What is adolescence?
19.Write a short note on puberty.
20.What are secondary sexual characters?
21.Name the male and female sex hormones.
22.What are the main changes that happen at puberty? (the 8 points without explanation -
from this PPT)

52. THANK YOU
Prepared by:
Narayanan Nampoothiri K P