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REACHING THE AGE OF ADOLESCENCEIn the previous chapter, you havelearnt how animals reproduce. It isonly after ‘growing up’ to a certainage that human beings and many otheranimals can reproduce. Why canhumans reproduce only after a certainage?In this chapter, you will learn aboutchanges that take place in the humanbody after which a person becomescapable of reproduction.In Chapter 9, you have learnt abouthuman reproductive organs. Here, weshall discuss the role that hormones playin bringing about changes that make achild grow into an adult.10.1 Adolescence and PubertyBoojho was celebrating his 12thbirthday. After his friends left, Boojhoand Paheli began chatting with theirparents. Paheli studies in an all-girlsschool. She started laughing. Sheremarked that many of Boojho’s schoolfriends, whom she met after a year, hadsuddenly shot up in height. Some ofthem were looking very funny with ahairy line above their lips. Her motherexplained that the boys had grown up.Growth begins from the day one isborn. But upon crossing the age of 10or 11, there is a sudden spurt in growthwhich becomes noticeable. The changestaking place in the body are part ofgrowing up. They indicate that you areno longer a child but are on the way tobecoming an adult.I wonder how long thisperiod marked by changesin the body will last!It is a strange period of lifewhen you are neither a child noran adult. I wonder whether thisperiod between childhood andadulthood had a special name!Growing up is a natural process. Theperiod of life, when the body undergoeschanges, leading to reproductivematurity, is called adolescence.Adolescence begins around the age of11 and lasts upto 18 or 19 years of age.Since this period covers the ‘teens’ (13to 18 or 19 years of age), adolescentsare also called ‘teenagers’. In girls,adolescence may begin a year or twoearlier than in boys. Also, the period ofadolescence varies from person to person.The human body undergoes severalchanges during adolescence. Thesechanges mark the onset of puberty. Themost important change which markspuberty is that boys and girls becomecapable of reproduction. Puberty endswhen an adolescent reaches reproductivematurity.2022-23
the tallest and who might be theshortest in your class.Paheli and Boojhorealised that suddenincrease in height andhairy line above the lipsin boys were signs ofadolescence. Theywanted to know moreabout other changes atpuberty.Age inYears10.2 Changes at PubertyIncrease in HeightThe most conspicuous change duringpuberty is the sudden increase inheight. At this time the long bones, thatis, the bones of the arms and the legselongate and make a person tall.Activity 10.1The following chart gives theaverage rate of growth in height ofboys and girls with age. The figuresin columns 2 and 3, give thepercentage of the height a personhas reached at the age given incolumn 1. For example, by the age11, a boy has reached 81% of hisprobable full height, while a girlhas reached 88% of her fullheight. These figures are onlyrepresentative and there may beindividual variations.Use the Table for your friendsand work out how tall they are likelyto be. Find out who is likely to be% of full 0%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 cmtall. At the end of the growth periodhe is likely to be120 100 cm 160 cm tall75114SCIENCE2022-23
Activity 10.2There is no need for Paheli to worry.All parts of the body do not grow at thesame rate. Sometimes the arms and legsor hands and feet of adolescents lookoversized and out of proportion with thebody. But soon the other parts catchup and result in a proportionate body.You must have noticed that heightof an individual is more or less similarto that of some family member. This isbecause height depends on the genesinherited from parents. It is, however,very important to eat the right kind offood during these growing years. Thishelps the bones, muscles and otherparts of the body get adequatenourishment for growth. You will findnutritional needs of adolescentsdiscussed later in the lesson.Use the data given in Activity 10.1to draw a graph. Take age on the Xaxis and per cent growth in heighton the Y-axis. Highlight the pointrepresenting your age on the graph.Find out the percentage of heightyou have already reached. Calculatethe height you might eventuallyreach. Tally your graph with the onegiven here (Fig. 10.1).Change in Body ShapeFig. 10.1 : Graph showing percentage of heightwith ageInitially, girls grow faster than boysbut by about 18 years of age, both reachtheir maximum height. The rate ofgrowth in height varies in differentindividuals. Some may grow suddenlyat puberty and then slow down, whileothers may grow gradually.Have you noticed that boys in your classhave broader shoulders and wider cheststhan boys in junior classes? This isbecause they have entered the age ofpuberty when shoulders generallybroaden as a result of growth. In girls,the region below the waist becomeswider.In boys, the muscles of the body growmore prominently than in the girls.Thus, changes occurring in adolescentboys and girls are different.Voice ChangeI am worried. Though Ihave become taller, myface looks much smallercompared to my body.Did you notice that sometimes the voiceof some of the boys in your class cracks?At puberty, the voice box or the larynxbegins to grow. Boys develop larger voiceboxes. The growing voice box in boys canbe seen as a protruding part of the throat115REACHING THE AGE OF ADOLESCENCE2022-23
called Adam’s apple (Fig. 10.2). In girls,the larynx is hardly visible from theoutside because of its small size.Generally, girls have a high pitched voice,whereas boys have a deep voice. Inadolescent boys, sometimes, the musclesof the growing voice box go out of controland the voice becomes hoarse. This statemay remain for a few days or weeks afterwhich the voice becomes normal.Adam’sappleand pimples on the face at this timebecause of the increased activity of theseglands in the skin.Development of Sex OrgansLook up Fig. 9.1 and 9.3 of theprevious lesson which show sexorgans of humans. At puberty, malesex organs like the testes and penisdevelop completely. The testes alsobegin to produce sperms. In girls, theovaries enlarge and eggs begin tomature. Also ovaries start releasingmature eggs.Reaching Mental, Intellectual andEmotional MaturityFig. 10.2 : Adam’s apple in a grown up boyMany of my classmateshave a hoarse voice. Now Iknow why?Increased Activity of Sweat andSebaceous GlandsDuring puberty the secretion of sweatglands and sebaceous glands (oil glands)increases. Many young people get acneA few glands such as sweat glands,oil glands and salivary glands releasetheir secretions through ducts.Endocrine glands release hormonesdirectly into the bloodstream. So, theyare also termed ductless glands.Adolescence is also a period of changein a person’s way of thinking.Adolescents are more independent thanbefore and are also self conscious.Intellectual development takes place andthey tend to spend considerable timethinking. In fact, it is often the time inone’s life when the brain has thegreatest capacity for learning.Sometimes, however, an adolescent mayfeel insecure while trying to adjust tothe changes in the body and mind. Butas adolescent learners, you should knowthat there is no reason to feel insecure.These changes are a natural part ofgrowing up.10.3 Secondary SexualCharactersYou have learnt in Chapter 9, thattestes and ovaries are the reproductiveorgans. They produce the gametes,that is, sperms and ova. In girls,breasts begin to develop at puberty116SCIENCE2022-23
and boys begin to grow facial hair, thatis, moustaches and beard. As thesefeatures help to distinguish the malefrom the female they are calledsecondary sexual characters. Boysalso develop hair on their chest. Inboth, boys and girls, hair grows underthe arms and in the region above thethighs or the pubic region.The testes and ovaries secrete sexhormones. You have just learnt thatthese hormones are responsible for themale and female secondary sexualcharacters. Further, the sex hormonesare under the control of hormones fromthe pituitary gland (Fig. 10.3). Thepituitary secretes many hormones, oneof which makes ova mature in theovaries and sperms form in the testes.Both Boojho and Paheli wish to knowwhat initiates changes at puberty.The changes which occur atadolescence are controlled byhormones. Hormones are chemicalsubstances. These are secretions fromendocrine glands, or endocrine system.The male hormone or testosteronebegins to be released by the testes atthe onset of puberty. This causeschanges in boys about which you havejust learnt, for example, the growth offacial hair. Once puberty is reached ingirls, ovaries begin to produce the femalehormone or estrogen which makes thebreasts develop. Milk secreting glandsor mammary glands develop inside thebreasts. The production of thesehormones is under the control ofanother hormone secreted from anendocrine gland called pituitary gland.Fig. 10.3 : The onset of puberty is controlled byhormones10.4 Role of Hormones inInitiating ReproductiveFunctionEndocrine glands release hormonesinto the bloodstream to reach aparticular body part called target site.The target site responds to thehormone. There are many endocrineglands or ductless glands in the body.Paheli and Boojho have nowunderstood that puberty marks thebeginning of the reproductive periodwhen one becomes capable ofreproduction. But they want to knowif reproductive life, once begun,continues, or it ends some time.117REACHING THE AGE OF ADOLESCENCE2022-23
10.5 Reproductive Phase ofLife in HumansAdolescents become capable ofreproduction when their testes andovaries begin to produce gametes. Thecapacity for maturation and productionof gametes lasts for a much longer timein males than in females.In females, the reproductive phase oflife begins at puberty (10 to 12 years ofage) and generally lasts till the age ofapproximately 45 to 50 years. The ovabegin to mature with the onset ofpuberty. One ovum matures and isreleased by one of the ovaries once inabout 28 to 30 days. During thisperiod, the wall of the uterus becomesthick so as to receive the egg, in caseit is fertilised and begins to develop.This results in pregnancy. Iffertilisation does not occur, thereleased egg, and the thickened liningof the uterus along with its bloodvessels are shed off. This causesbleeding in women which is calledmenstruation. Menstruation occursonce in about 28 to 30 days. The firstmenstrual flow begins at puberty andis termed menarche. At 45 to 50 yearsof age, the menstrual cycle stops.Stoppage of menstruation is termedmenopause. Initially, menstrual cyclemay be irregular. It take some time tobecome regular.Paheli says that thereproductive life of awoman lasts frommenarche to menopause.Is she right?Menstrual cycle is controlled byhormones. The cycle includes thematuration of the egg, its release,thickening of uterine wall and itsbreakdown if pregnancy does notoccur. In case the egg is fertilised itbegins to divide and then getsembedded in the uterus for furtherdevelopment as you have learnt inChapter 9 (Fig. 9.8).10.6 How is the Sex of theBaby Determined?I heard my mother and myaunt talking about my cousinwho is going to have a baby.They were discussing whethershe would give birth to a boyor a girl. I wonder what makesthe fertilised egg developeither into a boy or a girl!Boy or Girl?Inside the fertilised egg or zygote is theinstruction for determining the sex ofthe baby. This instruction is present inthe thread-like structures, calledchromosomes in the fertilised egg.Recall from Chapter 8, thatchromosomes are present inside thenucleus of every cell. All human beingshave 23 pairs of chromosomes in thenuclei of their cells. Two chromosomesout of these are the sex chromosomes,named X and Y. A female has two Xchromosomes, while a male has one Xand one Y chromosome. The gametes(egg and sperm) have only one set ofchromosomes. The unfertilised eggalways has one X chromosome. But118SCIENCE2022-23
sperms are of two kinds. One kind hasan X chromosome, and the other kindhas a Y chromosome.See Fig. 10.4. When a spermcontaining X chromosome fertilises theegg, the zygote would have two Xchromosomes and develop into a femalechild. If the sperm contributes a Ychromosome to the egg (ovum) atfertilisation, the zygote would developinto a male child.and ovaries to produce their hormones.You have alr eady learnt that thepituitary gland is an endocrine gland.It is attached to the brain.Apart from the pituitary, the testesand the ovaries, there are otherendocrine glands in the body such asthyroid, pancreas and adrenals(Fig. 10.5).pituitaryglandspermsthyroid glandadrenalglandeggspancreasposition ofthe ovary inthe femaleboygirltestisFig. 10.4 : Sex determination in humansNow you know that the sexchromosomes of the father determine thesex of an unborn baby. The belief thatthe mother is responsible for the sex ofher baby is completely wrong and toblame her for this is totally unjustified.10.7 Hormones other thanSex HormonesLook at Fig. 10.3 again. The hormonessecreted by the pituitary stimulate testesFig. 10.5 : Position of endocrine glands in thehuman bodyBoojho and Paheli had once visitedtheir aunt who was a doctor andremembered that a boy named Kaka hada very big and bulging throat. Their aunthad told them that Kaka was sufferingfrom ‘goitre’, a disease of the thyroidgland. Kaka’s thyroid gland was notproducing the hormone thyroxine.119REACHING THE AGE OF ADOLESCENCE2022-23
Their aunt also told them that theiruncle was suffering from ‘diabetes’because his pancreas was not producingthe hormone insulin in sufficientquantities. Boojho and Paheli thenasked their aunt about the adrenalglands, which are also shown in thechart hung on the wall of her clinic. Theaunt told them that adrenal glandssecrete hormones which maintain thecorrect salt balance in the blood.Adrenals also produce the hormoneadrenalin. It helps the body to adjustto stress when one is very angry,embarrassed or worried.Thyroid and adrenals secrete theirhormones when they receive orders fromthe pituitary through its hormones.Pituitary also secretes growth hormonewhich is necessary for the normalgrowth of a person.Are there hormones inother animals also? Havethey any role to play inreproduction?This change from larva to adult iscalled metamorphosis (Fig. 9.10).Metamorphosis in insects is controlledby insect hormones. In a frog, it iscontrolled by thyroxine, the hormoneproduced by thyroid. Thyroxineproduction requires the presence ofiodine in water. If the water in whichthe tadpoles are growing does notcontain sufficient iodine, the tadpolescannot become adults.If people do not haveenough iodine in their diet,will they get goitre causedby lack of thyroxine?Activity 10.3Collect information from magazinesor from doctors and prepare a noteon the importance of consumingiodised salt. You can also look forthis information on the internet.10.9 Reproductive Health10.8 Role of Hormones inCompleting the LifeHistory of Insects andFrogsYou have already learnt about the lifehistory of the silk moth and the frog.The caterpillar has to pass throughvarious stages to become an adult moth.Recall from Class VII the stages of thelife history of the silk moth. Similarly,the tadpole passes through certainstages to become a frog (Chapter 9).The physical and mental well being ofan individual is regarded as anindividual’s health. To keep the bodyhealthy, every human being, at any age,needs to have a balanced diet. Theperson must also observe personalhygiene and undertake adequatephysical exercise.During adolescence, however, thesebecome even more essential as the bodyis growing.Nutritional Needs of the AdolescentsAdolescence is a stage of rapid growthand development. Hence the diet for an120SCIENCE2022-23
adolescent has to be carefully planned.You have already learnt what a balanceddiet is. Recall that a balanced diet meansthat the meals include proteins,carbohydrates, fats and vitamins inrequisite proportions. Our Indian mealof roti/rice, dal (pulses) and vegetablesis a balanced meal. Milk is a balancedfood in itself. Fruits also providenourishment. For infants, mother’s milkprovides all the nourishment that theyneed.Iron builds blood and iron-rich foodsuch as leafy vegetables, jaggery, meat,citrus, Indian gooseberry (amla) are goodfor adolescents.Check items for lunch and dinner inyour meal. Is the meal balanced andnutritious? Does it include cerealswhich give energy and milk, meat, nutsand pulses which provide proteins forgrowth? Also, does it include fats andsugar that give energy? What aboutfruits and vegetables which areprotective foods? Chips and packed ortinned snacks, though very tastyshould never replace regular meals asthey do not have adequate nutritionalvalue.Activity 10.5Get ideas from the pictures given inFig.10.6. Prepare charts or postersand paste them in the class so thatyou are aware of the diet foradolescents. You may use yourcreative ideas and present it like anadvertisement. You may evenorganise a competition on this topic.meatvegetablesmilk andeggsfruitsgrainsActivity 10.4Make a group with your friends.Write down the items of food in yourbreakfast, lunch and dinner youhad on the previous day. Identifythe items responsible for propergrowth. Also identified the junkfood that you consumed theprevious day.Fig. 10.6 : Nutritious items of foodPersonal HygieneEveryone should have a bath at leastonce everyday. It is more necessary forteenagers because the increased activityof sweat glands sometimes makes thebody smelly. All parts of the body shouldbe washed and cleaned everyday. If121REACHING THE AGE OF ADOLESCENCE2022-23
cleanliness is not maintained there arechances of catching bacterial infection.Girls should take special care ofcleanliness during the time of menstrualflow. They should keep track of theirmenstrual cycle and be prepared for theonset of menstruation. Use sanitarynapkin or clean homemade pads.Change pads after every 4–5 hours asper the requirement.Physical exerciseWalking and playing in fresh air keepsthe body fit and healthy. All young boysand girls should take walks, exerciseand play outdoor games.Myths, Taboos, Do’s and Don’tsYou have learnt here and from Chapter9 the scientific facts related to humanreproduction. There are many wrongnotions which you should now be ableto discard as informed adolescents. Forexample, there are myths and taboosregarding bodily changes thatadolescents experience. Some of theseare given below and you can now arguewhy these are myths and not facts.1. A girl becomes pregnant ifshe looks at boys duringmenstruation.2. The mother is responsible for thesex of her child.3. A girl should not be allowed towork in the kitchen duringmenstruation.You may come across many other mythsand taboos. Discard them.Activity 10.6Collect data on the number ofchildren in your class who exerciseregularly and who do not exerciseregularly. Did you notice anydifference in their fitness andhealth? Prepare a report on thebenefits of regular exercise.Say “NO” to DrugsAdolescence is a period of muchactivity in the body and mind whichis a normal part of growing up. So donot feel confused or insecure. Ifanybody suggests that you will getrelief if you take some drugs, just say‘No’ unless prescribed by the doctor.Drugs are addictive. If you take themonce, you feel like taking them againand again. They harm the body in thelong run. They ruin health andhappiness.You must have heard about AIDSwhich is caused by a dangerous virus,HIV. This virus can pass on to anormal person from an infectedperson by sharing the syringes usedfor injecting drugs. It can also betransmitted to an infant from theinfected mother through her milk. Thevirus can also be transmitted throughsexual contact with a person infectedwith HIV.Adolescent PregnancyYou might be knowing that in our country, the legal age for marriage is 18 yearsfor girls and 21 years for boys. This is because teenage mothers are not preparedmentally or physically for motherhood. Early marriage and motherhood cause healthproblems in the mother and the child. It also curtails employment opportunities forthe young woman and may cause mental agony as she is not ready forresponsibilities of motherhood.122SCIENCE2022-23
KEYWORDSADAM’S APPLEWHAT YOU HAVE LEARNTWHATYOUHAVEÜHumans become capable of reproduction after puberty sets in. Children between the agesADOLESCENCEof 11 and 19 years are called adolescents.ADRENALINÜthe reproductive organs. Hair grow atBALANCED DIETvarious places on the body. Breasts developENDOCRINE GLANDSin girls and facial hair (moustache and beard)appear in boys. Voice of boys becomes hoarseESTROGENHORMONESINSULINLARYNXThe onset of puberty brings about growth ofas voice box enlarges during adolescence.ÜChildren gain height during adolescence.ÜThe onset of puberty and maturity ofreproductive parts are controlled by hormones.ÜHormones are secretions of endocrine glandswhich pour them directly into the blood stream.PITUITARY GLANDÜPituitary gland secretes hormones which include growth hormone and hormones thatPUBERTYmake other glands such as the testes, ovaries,REPRODUCTIVEthyroids and adrenals, secrete hormones.HEALTHPancreas secretes insulin, thyroid producesSECONDARY SEXUALthyroxine and adrenals produce adrenalin.CHARACTERSÜTestosterone is the male hormone andestrogen, the female hormone. The uterine wallSEX CHROMOSOMESin females prepares itself to receive thedeveloping fertilised egg. In case there is noTARGET SITEfertilisation, the thickened lining of the uterineTESTOSTERONETHYROXINEwall breaks down and goes out of the bodyalong with blood. This is called menstruation.ÜVOICE BOXSex of the unborn child depends on whetherthe zygote has XX or XY chromosomes.ÜIt is important to eat balanced food CHING THE AGE OF ADOLESCENCE2022-23
Exercises1.What is the term used for chemical secretions of endocrine glandsresponsible 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 glandsand 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 theirbody.(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.124SCIENCE2022-23
EXERCISES9.Word game : Use the clues to work out the words.Across3.Protruding voice box in boys4.Glands without ducts7.Endocrine gland attached to brain8.Secretion of endocrine glands9.Pancreatic hormone10. Female hormoneDown1.Male hormone2.Secretes thyroxine3.Another term for teenage5.Hormone reaches here through blood stream6.Voice box7.Term for changes at adolescence125REACHING THE AGE OF ADOLESCENCE2022-23
10. The table below shows the data on likely heights of boys and girls as theygrow in age. Draw graphs showing height and age for both boys andgirls on the same graph paper. What conclusions can be drawn fromthese graphs?Age(Years)Height 3165Extended Learning — Activities and Projects1.Find out from your elder relatives about their awareness of thelegal status of early marriage. You yourself may get information onit from your teacher, parents, a doctor or the internet. Write a twominute speech explaining why early marriage is not good for thecouple.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 adolescentfemales 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. Whyis its use for identification of sex of the unborn child bannedin India?Put your ideas together and write a short note on the importance ofknowing facts about reproduction.For more information visit :l www.teenshealth.org/teen/sexual health/l www.adolescenthealth.com126SCIENCE2022-23
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
