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REACHING THE AGE OF ADOLESCENCE, , I, , n the previous chapter, you have, learnt how animals reproduce. It is, only after ‘growing up’ to a certain, age that human beings and many other, animals can reproduce. Why can, humans reproduce only after a certain, age?, In this chapter, you will learn about, changes that take place in the human, body after which a person becomes, capable of reproduction., In Chapter 9, you have learnt about, human reproductive organs. Here, we, shall discuss the role that hormones play, in bringing about changes that make a, child grow into an adult., , 10.1 Adolescence and Puberty, Boojho was celebrating his 12th, birthday. After his friends left, Boojho, and Paheli began chatting with their, parents. Paheli studies in an all-girls, school. She started laughing. She, remarked that many of Boojho’s school, friends, whom she met after a year, had, suddenly shot up in height. Some of, them were looking very funny with a, hairy line above their lips. Her mother, explained that the boys had grown up., Growth begins from the day one is, born. But upon crossing the age of 10, or 11, there is a sudden spurt in growth, which becomes noticeable. The changes, taking place in the body are part of, growing up. They indicate that you are, , no longer a child but are on the way to, becoming an adult., , I wonder how long this, period marked by changes, in the body will last!, , It is a strange period of life, when you are neither a child nor, an adult. I wonder whether this, period between childhood and, adulthood had a special name!, , Growing up is a natural process. 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’ (13, to 18 or 19 years of age), 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 human body undergoes several, changes during adolescence. These, changes mark the onset of puberty. The, most important change which marks, puberty is that boys and girls become, capable of reproduction. Puberty ends, when an adolescent reaches reproductive, maturity., , 2021–22

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the tallest and who might be the, shortest in your class., Paheli and Boojho, realised that sudden, increase in height and, hairy line above the lips, in boys were signs of, adolescence. They, wanted to know more, about other changes at, puberty., , Age in, Years, , 10.2 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., , Activity 10.1, The following chart gives the, average rate of growth in height of, boys and girls with age. The figures, in columns 2 and 3, give the, percentage of the height a person, has reached at the age given in, column 1. For example, by the age, 11, a boy has reached 81% of his, probable full height, while a girl, has reached 88% of her full, height. These figures are only, representative and there may be, individual variations., Use the Table for your friends, and work out how tall they are likely, to be. Find out who is likely to be, , % of full height, Boys, Girls, , 8, , 72%, , 77%, , 9, , 75%, , 81%, , 10, , 78%, , 84%, , 11, , 81%, , 88%, , 12, , 84%, , 91%, , 13, , 88%, , 95%, , 14, , 92%, , 98%, , 15, , 95%, , 99%, , 16, , 98%, , 99.5%, , 17, , 99%, , 100%, , 18, , 100%, , 100%, , Calculation for full height (cm), Present height (cm), × 100, % of full height at this age, (as given in the chart), , Example:, A boy is 9 years old and 120 cm, tall. At the end of the growth period, he is likely to be, 120, × 100 cm = 160 cm tall, 75, , 114, , SCIENCE, , 2021–22

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Activity 10.2, , There is no need for Paheli to worry., All parts of the body do not grow at the, same rate. Sometimes the arms and legs, or hands and feet of adolescents look, oversized and out of proportion with the, body. But soon the other parts catch, up and result in a proportionate body., You must have noticed that 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. You will find, nutritional needs of adolescents, discussed later in the lesson., , Use the data given in Activity 10.1, to draw a graph. Take age on the Xaxis and per cent growth in height, on the Y-axis. Highlight the point, representing your age on the graph., Find out the percentage of height, you have already reached. Calculate, the height you might eventually, reach. Tally your graph with the one, given here (Fig. 10.1)., , Change in Body Shape, , Fig. 10.1 : Graph showing percentage of height, with age, , Initially, girls grow faster than boys, but by about 18 years of age, both reach, their maximum height. The rate of, growth in height varies in different, individuals. Some may grow suddenly, at puberty and then slow down, while, others may grow gradually., , Have you noticed that boys in your class, have broader shoulders and wider chests, than boys in junior classes? This is, because they have entered the age of, puberty when 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., Thus, changes occurring in adolescent, boys and girls are different., Voice Change, , I am worried. Though I, have become taller, my, face looks much smaller, compared to my body., , Did you notice that sometimes the voice, of some of the boys in your class cracks?, At puberty, the voice box or the larynx, begins to grow. Boys develop larger voice, boxes. The growing voice box in boys can, be seen as a protruding part of the throat, 115, , REACHING THE AGE OF ADOLESCENCE, , 2021–22

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called Adam’s apple (Fig. 10.2). 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. In, adolescent boys, sometimes, the muscles, of the growing voice box go out of control, and the voice becomes hoarse. This state, may remain for a few days or weeks after, which the voice becomes normal., , Adam’s, apple, , and pimples on the face at this time, because of the increased activity of these, glands in the skin., Development of Sex Organs, Look up Fig. 9.1 and 9.3 of the, previous lesson which show sex, organs of humans. 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, , Fig. 10.2 : Adam’s apple in a grown up boy, , Many of my classmates, have a hoarse voice. Now I, know why?, , 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, A few glands such as sweat glands,, oil glands and salivary glands release, their secretions through ducts., Endocrine glands release hormones, directly into the bloodstream. So, they, are also termed ductless glands., , Adolescence is also a period of change, in a person’s way of thinking., Adolescents are more independent than, before and are also self conscious., Intellectual development takes place and, they tend to spend considerable time, thinking. In fact, it is often the time in, one’s life when the brain has the, greatest capacity for learning., Sometimes, however, an adolescent may, feel insecure while trying to adjust to, the changes in the body and mind. But, as adolescent learners, you should know, that there is no reason to feel insecure., These changes are a natural part of, growing up., , 10.3 Secondary Sexual, Characters, You have learnt in Chapter 9, that, testes and ovaries are the reproductive, organs. They produce the gametes,, that is, sperms and ova. In girls,, breasts begin to develop at puberty, , 116, , SCIENCE, , 2021–22

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and boys begin to grow facial hair, that, is, moustaches and beard. As these, features help to distinguish the male, from the female they are called, secondary sexual characters. Boys, also develop hair on their chest. In, both, boys and girls, hair grows under, the arms and in the region above the, thighs or the pubic region., , The testes and ovaries secrete sex, hormones. You have just learnt that, 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 (Fig. 10.3). The, pituitary secretes many hormones, one, of which makes ova mature in the, ovaries and sperms form in the testes., , Both Boojho and Paheli wish to know, what initiates changes at puberty., , 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 hormone or testosterone, begins to be released by the testes at, the onset of puberty. This causes, changes in boys about which you have, just learnt, for example, the growth of, facial hair. Once puberty is reached in, girls, ovaries begin to produce the female, hormone or estrogen which makes the, breasts develop. Milk secreting glands, or mammary glands develop inside the, breasts. The production of these, hormones is under the control of, another hormone secreted from an, endocrine gland called pituitary gland., Fig. 10.3 : The onset of puberty is controlled by, hormones, , 10.4 Role of Hormones in, Initiating Reproductive, Function, Endocrine glands release hormones, into the bloodstream to reach a, particular body part called target site., The target site responds to the, hormone. There are many endocrine, glands or ductless glands in the body., , Paheli and Boojho have now, understood that puberty marks the, beginning of the reproductive period, when one becomes capable of, reproduction. But they want to know, if reproductive life, once begun,, continues, or it ends some time., 117, , REACHING THE AGE OF ADOLESCENCE, , 2021–22

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10.5 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. The ova, begin to mature with the onset of, puberty. 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 so as to receive the egg, in case, it is fertilised and begins to develop., This results in pregnancy. If, fertilisation 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 is called, menstruation. 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. Initially, menstrual cycle, may be irregular. It take some time to, become regular., , Paheli says that the, reproductive life of a, woman lasts from, menarche to menopause., Is she right?, , 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 as you have learnt in, Chapter 9 (Fig. 9.8)., , 10.6 How is the Sex of the, Baby Determined?, , I heard my mother and my, aunt talking about my cousin, who is going to have a baby., They were discussing whether, she would give birth to a boy, or a girl. I wonder what makes, the fertilised egg develop, either into a boy or a girl!, , Boy or Girl?, Inside the fertilised egg or zygote is the, instruction for determining the sex of, the baby. This instruction is present in, the thread-like structures, called, chromosomes in the fertilised egg., Recall from Chapter 8, that, 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 unfertilised egg, always has one X chromosome. But, , 118, , SCIENCE, , 2021–22

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sperms are of two kinds. One kind has, an X chromosome, and the other kind, has a Y chromosome., See Fig. 10.4. 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., , and ovaries to produce their hormones., You have alr eady learnt that the, pituitary gland is an endocrine gland., It is attached to the brain., Apart from the pituitary, the testes, and the ovaries, there are other, endocrine glands in the body such as, thyroid, pancreas and adrenals, (Fig. 10.5)., , pituitary, gland, , sperms, , thyroid gland, , adrenal, gland, eggs, pancreas, , position of, the ovary in, the female, boy, , girl, , testis, , Fig. 10.4 : Sex determination in humans, , Now you know that 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., , 10.7 Hormones other than, Sex Hormones, Look at Fig. 10.3 again. The hormones, secreted by the pituitary stimulate testes, , Fig. 10.5 : Position of endocrine glands in the, human body, , Boojho and Paheli had once visited, their aunt who was a doctor and, remembered that a boy named Kaka had, a very big and bulging throat. Their aunt, had told them that Kaka was suffering, from ‘goitre’, a disease of the thyroid, gland. Kaka’s thyroid gland was not, producing the hormone thyroxine., 119, , REACHING THE AGE OF ADOLESCENCE, , 2021–22

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Their aunt also told them that their, uncle was suffering from ‘diabetes’, because his pancreas was not producing, the hormone insulin in sufficient, quantities. Boojho and Paheli then, asked their aunt about the adrenal, glands, which are also shown in the, chart hung on the wall of her clinic. The, aunt told them that adrenal glands, secrete hormones which maintain the, correct salt balance in the blood., Adrenals also produce the hormone, adrenalin. It helps the body to adjust, to stress when one is very angry,, embarrassed or worried., Thyroid and adrenals secrete their, hormones when they receive orders from, the pituitary through its hormones., Pituitary also secretes growth hormone, which is necessary for the normal, growth of a person., , Are there hormones in, other animals also? Have, they any role to play in, reproduction?, , This change from larva to adult is, called metamorphosis (Fig. 9.10)., Metamorphosis in insects is controlled, by insect hormones. In a frog, it 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., , If people do not have, enough iodine in their diet,, will they get goitre caused, by lack of thyroxine?, , Activity 10.3, Collect information from magazines, or from doctors and prepare a note, on the importance of consuming, iodised salt. You can also look for, this information on the internet., , 10.9 Reproductive Health, , 10.8 Role of Hormones in, Completing the Life, History of Insects and, Frogs, You have already learnt about the life, history of the silk moth and the frog., The caterpillar has to pass through, various stages to become an adult moth., Recall from Class VII the stages of the, life history of the silk moth. Similarly,, the tadpole passes through certain, stages to become a frog (Chapter 9)., , 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., Nutritional Needs of the Adolescents, Adolescence is a stage of rapid growth, and development. Hence the diet for an, , 120, , SCIENCE, , 2021–22

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adolescent has to be carefully planned., You have already learnt what a balanced, diet is. Recall that 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., Check items for lunch and dinner in, your meal. Is the meal balanced and, nutritious? Does it include cereals, which give energy and milk, meat, nuts, and pulses which provide proteins for, growth? Also, does it include fats and, sugar that give energy? What about, fruits and vegetables which are, protective foods? Chips and packed or, tinned snacks, though very tasty, should never replace regular meals as, they do not have adequate nutritional, value., , Activity 10.5, Get ideas from the pictures given in, Fig.10.6. Prepare charts or posters, and paste them in the class so that, you are aware of the diet for, adolescents. You may use your, creative ideas and present it like an, advertisement. You may even, organise a competition on this topic., , meat, vegetables, milk and, eggs, , fruits, , grains, , Activity 10.4, Make a group with your friends., Write down the items of food in your, breakfast, lunch and dinner you, had on the previous day. Identify, the items responsible for proper, growth. Also identified the junk, food that you consumed the, previous day., , Fig. 10.6 : Nutritious items of food, , 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, 121, , REACHING THE AGE OF ADOLESCENCE, , 2021–22

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cleanliness is not maintained there are, chances of catching bacterial infection., Girls should take special care of, cleanliness during the time of 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 after every 4–5 hours as, per the requirement., 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., Myths, Taboos, Do’s and Don’ts, You have learnt here and from Chapter, 9 the scientific facts related to human, reproduction. There are many wrong, notions which you should now be able, to discard as informed adolescents. For, example, there are myths and taboos, regarding bodily changes that, adolescents experience. Some of these, are given below and you can now argue, why these are myths and not facts., 1. A girl becomes pregnant if, she looks at boys during, menstruation., 2. The mother is responsible for the, sex of her child., 3. A girl should not be allowed to, work in the kitchen during, menstruation., You may come across many other myths, and taboos. Discard them., , Activity 10.6, Collect data on the number of, children in your class who exercise, regularly and who do not exercise, regularly. Did you notice any, difference in their fitness and, health? Prepare a report on the, benefits of regular exercise., , Say “NO” to Drugs, 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., You must have heard about AIDS, which is caused by a dangerous virus,, HIV. This virus can pass on to a, normal person from an infected, person 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., , 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., 122, , SCIENCE, , 2021–22

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KEYWORDS, ADAM’S APPLE, , T Y, VE LEARNT, YOU, WHAT, HAVE, WHA, OU HA, Ü, , Humans become capable of reproduction after puberty sets in. Children between the ages, , ADOLESCENCE, , of 11 and 19 years are called adolescents., ADRENALIN, , Ü, , the reproductive organs. Hair grow at, , BALANCED DIET, , various places on the body. Breasts develop, , ENDOCRINE GLANDS, , in girls and facial hair (moustache and beard), appear in boys. Voice of boys becomes hoarse, , ESTROGEN, HORMONES, INSULIN, LARYNX, , The onset of puberty brings about growth of, , as voice box enlarges during adolescence., Ü, , Children gain height during adolescence., , Ü, , The onset of puberty and maturity of, reproductive parts are controlled by hormones., , Ü, , Hormones are secretions of endocrine glands, which pour them directly into the blood stream., , PITUITARY GLAND, , Ü, , Pituitary gland secretes hormones which include growth hormone and hormones that, , PUBERTY, , make other glands such as the testes, ovaries,, REPRODUCTIVE, , thyroids and adrenals, secrete hormones., , HEALTH, , Pancreas secretes insulin, thyroid produces, , SECONDARY SEXUAL, , thyroxine and adrenals produce adrenalin., , CHARACTERS, , Ü, , Testosterone is the male hormone and, estrogen, the female hormone. The uterine wall, , SEX CHROMOSOMES, , in females prepares itself to receive the, developing fertilised egg. In case there is no, , TARGET SITE, , fertilisation, the thickened lining of the uterine, TESTOSTERONE, THYROXINE, , wall breaks down and goes out of the body, along with blood. This is called menstruation., Ü, , VOICE BOX, , Sex of the unborn child depends on whether, the zygote has XX or XY chromosomes., , Ü, , It is important to eat balanced food and, maintain, , personal, , hygiene, , during, , adolescence., , 123, , REACHING THE AGE OF ADOLESCENCE, , 2021–22

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Exercises, 1., , What is the term used for chemical secretions of endocrine glands, responsible for changes taking place in the body?, , 2., , Define adolescence., , 3., , What is menstruation? Explain., , 4., , List changes in the body that take place at puberty., , 5., , Prepare a Table having two columns depicting names of endocrine glands, and hormones secreted by them., , 6., , What are sex hormones? Why are they named so? State their function., , 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., , 8., , Write notes on—, (a), , Adam’s apple., , (b), , Secondary sexual characters., , (c), , Sex determination in the unborn baby., , 124, , SCIENCE, , 2021–22

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EXERCISES, , 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, , 125, , REACHING THE AGE OF ADOLESCENCE, , 2021–22

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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, , Extended Learning — Activities and Projects, 1., , Find out from your elder relatives about their awareness of the, legal status of early marriage. You yourself may get information on, it from your teacher, parents, a doctor or the internet. Write a twominute speech explaining why early marriage is not good for the, couple., , 2., , Collect newspaper cuttings and information in magazines about HIV/, AIDS. Write a one page article of 15 to 20 sentences on HIV/AIDS., , 3., , In our country, according to 2011 census, there are 940 adolescent, females for every 1000 males. Find out., , 4., , (a), , the concerns of the community regarding this low ratio., Remember that the chance of having a boy or a girl is equal., , (b), , what amniocentesis is and how useful this technique is. Why, is its use for identification of sex of the unborn child banned, in India?, , Put your ideas together and write a short note on the importance of, knowing facts about reproduction., For more information visit :, l www.teenshealth.org/teen/sexual_health/, l www.adolescenthealth.com, , 126, , SCIENCE, , 2021–22