1. Adolescence And Puberty-
ü Animals, as well as human beings, can reproduce only after a certain age or time period in their lives after growing up into an adult.
ü This is because of changes in hormones in their bodies that make them capable of reproduction.
ü Adolescence is a time period in life when the body leads to reproductive maturity and experiences some changes.
ü This time period may vary in different individuals.
ü The adolescence period includes the teenage and therefore adolescents are often called Teenagers as well.
Adolescent Period In | Begins At Age Around | Ends At Age Around |
Boys | 11 years | 18 or 19 years |
Girls | 10 or 11 years | 18 or 19 years |
ü Puberty is the time period in life when animals and human beings become capable of reproduction.
ü The changes that occur in the body during the adolescent age are an indication that an individual is reaching puberty.
Changes | Explanation |
The Height Increases Suddenly | The bones of the legs in the arms of a person start to grow longer and hence a person becomes taller in the puberty age. This increase in height occurs until the age of 18 in both boys and girls. However, it is observed that girls grow faster than boys initially.
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Change In The Shape Of The Body | As boys and girls enter into the time period of puberty their body shapes start to change. The boys generally experience a change in chest and shoulders as they become wider. In girls, the area below the waist becomes wider. However, the changes in boys and girls are different because the muscle growth in boys is higher than that in girls.
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Change In Voice | A change in voice is accomplished as the body hits puberty, especially in boys. The voice box or the larynx develops in boys. It can also be seen as an enlarged part of the throat in boys and is named as Adam's Apple. Boys also experience a hoarse voice for some time due to the changes in the larynx. The larynx in girls, on the other hand, is not visible because of its smaller size.
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Increased Sweat And Oil Production In The Skin | There are sweat glands and oil glands (called sebaceous glands) present in our bodies which start secreting more oil and sweat during the puberty age. Many times girls and boys get acne and pimples on the face during the excess secretion of these glands.
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Development Of Sex Organs | By the time girls and boys hit puberty the reproductive organs are developed completely. In males, the sperm production begins. In females, the size of the ovaries increases and it starts releasing the eggs.
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Mental, Emotional And Intellectual Maturity | During the adolescent age, the brain has the maximum learning power. The way of thinking of individuals starts to change. It is also observed that girls and boys start feeling self-conscious. They may also feel a little uncomfortable and insecure due to sudden changes in the body. However, all these changes are completely normal.
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Table 01- Changes in body
2. Secondary Sexual Characters-
ü At puberty, some changes occur in both males and females that distinguish them from each other. The features that develop in them are called Secondary Sexual Characters.
ü In boys some secondary sexual characters are- facial hair growth, growth of hair on the chest, under the arms and pubic area
ü Secondary sexual characteristics in girls are- development of breasts the growth of hair under the arms and the pubic area.
3. Changes In The Human Body Occur At The Time Of Puberty-
ü There are endocrine glands present in humans with secrete chemical substances in the body is called the Hormones.
ü These chemical substances are responsible for changes in the human body at the time of puberty.
ü The hormones act as messengers and are responsible for transporting signals for one cell to another.
ü Hence they evoke responses from various organs of the body and tissues. Hormones have certain properties or characteristics such as-
n They are secreted by the endocrine glands.
n They circulate in the body fluids.
n They are responsible for regulating the behaviour of the target cells.
n They cause long term effects in the body like change in behaviour, change in growth, development of organs, puberty menopause etc.
n Hormones are secreted in limited quantities from time to time whenever they are required by the body.
n Different glands present in the body are responsible for secretion of different hormones.
n The nervous system regulates the flow of hormones in the body.
4. Endocrine Glands-
ü The endocrine glands are also called Ductless Glands because they secrete the hormones directly into the blood.
ü In males, the testes secrete the male hormones or the testosterone.
ü In females, the ovaries secrete the female hormones or the estrogen.
Figure 01- Endocrine glands in humans
ü Pituitary Glands- There are pituitary glands present in the body switch control the production of the hormones by endocrine glands in both males as well as females.
ü Role Of Hormones In Initiating The Reproductive Function- The part of the body for which a particular hormone is meant is called the Target Site. The endocrine glands secrete the hormones in the blood and it reaches the target site. Then the target site response accordingly.
ü Reproductive Phase Of Life In Humans- The ability of production of gametes in humans last until certain time period only. This time period varies between males and females.
ü Reproductive Phase In Females- It begins from the age of 10 to 12 years and lasts until the age of 45 to 50 years. When females hit puberty, the eggs or ova start getting mature. One of the ovaries then releases the mature ovum around 28 to 30 days. The wall of the uterus at this time, when the egg is released, becomes thick to hold the egg in case if fertilization occurs and the egg develops.
5. Menstruation-
ü When the fertilization does not take place, the lining of the uterus sheds along with the egg and the blood vessels.
ü This results in menstruation or bleeding in females.
ü The first menstrual flow occurs at puberty and is called the Menarche.
ü When the menstrual flow stops, it is termed as Menopause.
ü The whole menstrual cycle occurs because of female hormones.
Figure 02- Menstruation cycle
6. Determining The Sex-
ü We know that there are 23 pairs of chromosomes present inside the nucleus of every human cell.
ü These chromosomes have a thread-like structure and they always occur in pairs.
ü The chromosomes help in determining the sex of the child.
ü Out of the 23 pairs of chromosomes, 2 of them are sex chromosomes called X and Y.
ü Females have two X chromosomes and males have one X and one Y chromosome.
ü The gametes contain only one set of chromosomes that is either an X or a Y.
ü The egg of the female contains an X chromosome always.
ü Although, the sperm can contain only one of the X and Y chromosomes.
ü So if the sperm that contains a Y chromosome fertilizes with the egg which contains the X chromosome, the zygote develops into a male.
ü On the other hand, if the sperm contains an X chromosome and fertilizers with the egg which contains X chromosome, the zygote develops into a female.
ü Hence the sex of the child depends upon the chromosomes of the father and not the mother.
Figure 03- Determination of sex
7. Non Sexual Hormones-
ü Insects like silk moths and some animals like frogs undergo the process of metamorphosis which results in drastic changes in their bodies.
ü The insect hormones control the process of metamorphosis in the insects.
ü In frogs, thyroid releases thyroxine which controls the process of metamorphosis in them.
ü The thyroxine only produces with the help of iodine that is present in the water.
ü If there is a lack of iodine in water the tadpoles would never turn into adult frogs.
8. Health-
Food Item | Major Nutrient | Function |
Pulses and nuts | Proteins | Growth, repair of body cells. |
Oranges and amla | Vitamin-C | Keep the body healthy by providing resistance. |
Sugar and roti | Carbohydrates | Provide energy |
Oils | Fats | Provide energy |
Vegetables | Vitamins and minerals | keep the body healthy and disease free. |
Table 03- Food items and their role
9. Personal Hygiene-
ü Personal hygiene also plays a role in maintaining the mental and physical well being of adolescents. Having bath daily as the sweat glands and the oil glands secrete high amounts of sweat and oil in the skin which can lead to bad odour.
ü Maintaining cleanliness of the body as there can be chances of getting a bacterial infection otherwise.
ü Females should take note of the menstrual cycle and prepare themselves accordingly.
10. Physical Exercise-
ü Exercising not only keep the body fit but also helps in relieving stress and maintaining mental well being.
ü Thus, adolescents should indulge in sports, exercises, walking, cycling and other physical activities.
11. Avoid Drugs-
ü Adolescent age incorporates different changes in the mind and body of the individual.
ü As a result, the adolescents may feel a little uneasy sometimes.
ü They should understand that this is natural and they should not be worried about it.
ü But many times the adolescents are fooled by others by saying that taking drugs would bring relief to them.
ü They should always say NO to that as taking drugs can be dangerous for their health.
ü Drugs should be taken only if a doctor prescribed them otherwise not.
ü This is because the drugs are addictive and once a person takes them they feel like taking them again and again.
ü As a result, the mental and physical health of the person starts getting affected due to drugs.
ü Also, taking drugs through syringes can cause AIDS (Acquired Immunodeficiency Disease).
ü This disease is caused by a hazardous virus that can get transmitted from an infected person to another through the use of same syringes.
ü Along with this, it can transmit through sexual contact or from the infected mother's milk.
NCERT PRACTRICE QUESTIONS
1. What is the term used for secretions of endocrine glands responsible for changes taking place in the body?
Ans.- Hormones
2. Define adolescence.
Ans.- The period of life, when the body undergoes changes, leading to reproductive maturity, is called adolescence. The period of adolescence is normally 11 years to 19 years.
3. What is menstruation? Explain.
Ans.- In females, the ova or eggs begin to mature with the onset of puberty (10 to 12 years of age) one egg get matured 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 so as to receive the fertilized egg. In case it is fertilized, it begins to develop. This results in pregnancy. If the fertilization fails to take place, the ovum or the released egg and the thickened lining of the uterus along with its blood vessels are shed off. This causes bleeding in women. This is called menstruation. It occurs once in 28 to 30 days.
4. List changes in the body that take place at puberty.
Ans.- The changes take place differently in the body of boys and girls at puberty. These change may be listed as below:
ü There is sudden increase in the height of both boys and girls. However, both reach their maximum height at the age of 17 to 18 years.
ü The voice of boys become hoarse and that of girls become shrill.
ü Shoulders become broader and muscles grow more prominently in boys. In girls, the regions below the waist becomes wider.
ü Hair start growing in different parts of boys and girls.
ü In most of the teenagers, due to increased secretion of sweat and sebaceous gland, get acne and pimples on their face.
ü Onset of puberty brings changes in secondary sexual characters in both male and female.
ü Boys and girls become capable of reproduction.
ü In girls, menstruation starts.
ü Different types of hormones start to release in initiating a reproductive function.
5. Prepare a table having two columns depicting names of endocrine glands and hormones secreted by them.
Ans.-
Endocrine glands | Hormones |
1. Pituitary gland | (i) Growth hormones |
2. Ovaries | (ii) Estrogen |
3. Testes | (iii) Testosterone |
4. Thyroid | (iv) Thyroxine |
5. Pancreas | (v) Insulin |
6. Adrenal glands | (vi) Adrenaline |
6. What are sex hormones? Why are they named so? State their function.
Ans.- The hormones which help and control the formation of secondary sexual characters are called sex hormones. They are named so because they control the sexual activities and are secreted by males and females separately. Functions of sex hormones are given below separately-
Male sex hormone- It is also called testosterone. It is secreted by testes and causes changes in secondary sexual character of boys like growth of facial hair like moustache, beard, etc. It also stimulates spermatogenesis.
Female sex hormone- It is also called estrogen. It is secreted by ovaries and controls the secondary sexual characters in females appearance of mammary glands, etc. It also maintains pregnancy.
7. Choose the correct option.
(a) Adolescents should be careful about what they eat, because:
(i) proper diet develops their brains. (ii) proper diet is needed for the rapid growth taking place in their body. (iii) adolescents feel hungry all the time. (iv) taste buds are well developed in teenagers.
(b) Reproductive age in women starts when their:
(i) menstruation starts. (ii) breasts start developing. (iii) body weight increases. (iv) height increases.
(c) The right meal for adolescents consists of:
(i) chips, noodles, coke. (ii) chapati, dal, vegetables. (iii) rice, noodles and burger. (iv) vegetable cutlets, chips and lemon drink.
Ans.- (a) (ii) (b) (i) (c) (ii)
8. Write notes on- (a) Adam’s apple (b) Secondary sexual characters. (c) Sex determination in the unborn baby.
Ans.- (a) Adam’s apple: During puberty, a change in the voice of boys and girls takes place due to increase in the size of the voice box or larynx. In boys, the voice box tends to protrude out on the upper part of the neck, below the chin and is often referred to as Adam’s apple.
(b) Secondary sexual characters: Those characters which are visible more apparently and help in distinguishing a male from a female are called secondary sexual characters. For example, in girls, breasts and in boys, facial hair, i.e., moustache and beard.
(c) Sex determination in the unborn baby: The sex of a child, i.e., whether it is a male or a female is determined at the time of fertilisation when a male gametes fuse with a female gamete. All human beings have 23 pairs of chromosomes in the nuclei of their cells. Two chromosomes out of these are sex chromosomes. 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 having X chromosome, and the other having 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 or ovum at fertilisation, the zygote would develop into a male child. It is thus also clear that the sex chromosomes of the father determine the sex of an unborn baby.
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
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?
Age (Years) | Height (cm) | |
Boys | Girls | |
0 | 53 | 53 |
4 | 96 | 92 |
8 | 114 | 110 |
12 | 129 | 133 |
16 | 150 | 150 |
20 | 173 | 165 |
Ans.- Based on the above graph, we conclude that initially boys grow faster than girls from 0-8 years, and girls grow faster than boys from 8-16 years. But both reach their maximum height at the age of 20. Here boys show a greater increase in height than girls.
Junior Science Topic - Reaching The Age Of Adolescence. Chapter notes, video lectures, power point presentation and NCERT exercise solution. (Class 8, CBSE syllabus, chapter 10)
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