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  • CBSEClass12Biology

    ImportantQuestions

    Chapter3

    HumanReproduction

    1MarksQuestions

    1. Failureoftestestodescendintoscrotalsacsleadstosterility.Why?

    Ans.Hightemperatureofabdomenkillsthespermatogenictissueofthetestes,sonosperm

    areformed.

    2. Bothvaccineandcolostrumproduceimmunity.Nametypeofimmunityproducedby

    these.

    Ans.VaccineActiveimmunityColostrumPassiveimmunity.

    3. Howmanyspermswillbeproducedfrom10primaryspermatocytesandhowmany

    eggswillbeproducedfrom10primaryoocytes?

    Ans.40sperms,10eggs.

    4. Thespermatogonialcellhas46chromosomesinhumanmale.Givethenumberof

    chromosomesin

    (a) Primaryspermatocyte(b)Spermatid

    Ans.(a)46inPrimaryspermatocyte

    (b) 23inspermatid.

    5. Inovarywhichstructuretransformsascorpusluteumandnamethehormone

    secretedbycorpusluteum?

    Ans.FollicularcellsofemptyGraafianfollicle.

  • Progesterone.

    6. “Eachandeverycoitusdoesnotresultsinfertilisationandpregnancy”.Justifythe

    statement.

    Ans.Ovumandspermshouldreachsimultaneouslytotheampullary–isthmicjunction.

    7. Whyaremaletesteslocatedoutsidetheabdominalcavity?

    Ans.Themaletestesarelocatedinthescrotumoutsidetheabdominalcavityasthescrotum

    provideslowtemperaturethanthenormalbodytemperaturerequiredforspermatogenesis.

    8. Statethefunctionofleydigcells.

    Ans.Theleydigcellssynthesiseandsecretetesticularhormonescalledandrogens.

    9. Wheredowefindfimbriae?

    Ans.Fimbriaearefingerlikeprojectionsfoundintheedgesoftheinfundibulum.

    10. Whatissemen?

    Ans.Theseminalplasmaalongwiththespermsconstitutessemen.

    11. Defineparturition.

    Ans.Thevigorouscontractionoftheuterusthatresultsintothedeliveryofthechildatthe

    endofpregnancyiscalledparturition.

    12. Wheredoesfertilizationnormallytakesplaceinahumanfemale.

    Ans.Ampulla(fallopiantube).

    13. Namethesubstancepresentinthespermacrosome&whichhelpinspermsentry

    intoegg.

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  • Ans.Acrosomecontainsenzymese.g.hyaluronidasethathelpsindissolvingmembraneof

    ovum.

    14. Namethelayerofcellsthatformstheouterwallofblastocyst.

    Ans.Trophoblast.

    15. Atwhatstageisthemammalianembryoimplantedinuterus?

    Ans.Blastocyststage.

    16. DespitethepresenceofSomanyspermsinthevicinityofaneggcell,onlyonesperm

    enterstheovum.Why?

    Ans.Becausewhenaspermcomesincontactwithovum(zonapellucida)&induceschanges

    inmembranetoblockentryofothersperms.

    17. Howmanypolarbodiesaregivenoutinproductionofoneeggduringcogenesis?

    Ans.Twopolarbodies

    2MarksQuestions

    1. Givethefunctionof

    (a) Corpusluteum

    (b) Endometrium

    Ans.Corpusluteum:Itsecretesprogesteronewhichpreparesendometriumofuterusfor

    implantationandnormaldevelopmentoffoetus.

    Endometrium:Itundergoescyclicchangesduringmenstrualcycleandpreparesitselffor

    implantationofblastocyst.

  • 2. Inthegivenfigure,givethenameandfunctionsofpartslabeledAandB.

    Ans.A=TrophoblastGetsattachedtoendometriumanddrawsnutritivematerialsecreted

    byuterineendometriumgland.

    B=InnercellmassDifferentiatesasEmbryo.

    3. Givenbelowisanincompleteflowchartshowinginfluenceofhormoneon

    gametogenesisinmale,observetheflowchartcarefullyandfillintheblankA,B,Cand

    D.

  • Ans.A=Testosterone;B=Spermatogenesis

    C=Sertolicells;DSpermiogenesis

    4. Givereasonforthefollowing:

    (a) Thefirsthalfofthemenstrualcycleiscalledfollicularphaseaswellasproliferative

    phase.

    (b) Thesecondhalfofthemenstrualcycleiscalledlutealphaseaswellassecretory

    phase.

    Ans.(a)Duringthisphase,primaryfolliclestransformintoGraafianfollicleunderFSH

    stimulation.GraafianfolliclessecreteestrogenswithstimulateenlargementofEndometrium

    ofuterus.

    (b) Duringthisphase,Corpusluteumisfullyformedandsecreteslargequantityof

    Progestrone.

    5. WhatismeantbyL.H.Surge?WritetheroleofL.H.

    Ans.Therearethreephasesinyourmenstrualcycle–follicularphase,ovulatoryphaseand

    lutealphase.Intermsoftheluteinizinghormone(LH)surge,theovulatoryphaseismost

    important.Duringthefollicularphasethefollicledevelopsatthebeginningofthemenstrual

    cycle.Thiscyclebeginswiththemenstrualperiod,thesheddingoftheiuterineliningandthe

    sheddingcleansestheliningoftheuterusinpreparationforovulationduringtheovulatory

    phase.

    6. Explainsignificanceoftheconditioninwhichthetestesremainsuspendedin

    scrotumoutsidetheabdomen.

    Ans.Humanspermcellscannotdevelopatbodytemperature.Spermatogenesisand

    maintenanceoftheseminiferoustubulesrequiresatemperatureslightlylowerthanthatof

    thebody.Thisisprovidedbythescrotum,whichliesoutsidetheabdominalcavity.

  • 7. Describethestructureofaspermwithadiagram.

    Ans.Thehumanspermisamicroscopicstructurewithahead,middlepieceandatail.The

    headhasthehaploidnucleusandananterioracrosomethatcontainstheenzymesrequired

    forthefertilizationoftheegg.Themiddlepiecehasnumerousmitochondriatoproducethe

    energyforthemobilityofthetailofthesperm.

    8. Enlistanytwofunctionsofafemaleplacenta.

    Ans.Thestructuralandthefunctionalunitbetweenthedevelopingembryoandthemother

    calledplacentafacilitatesthesupplyofnutrients,oxygentotheembryoandalsotheremoval

    ofcarbondioxideandotherexcretoryproductsproducedbytheembryo.Italsoactsas

    endocrinetissueandproducesseveralhormones

    9. Whatisthenumberofchromosomesinthefollowingcells?Primaryoocyte,

    secondaryoocyte,ootidandfollicle.

    Ans.Thenumberofchromosomeinthecellsisasfollows:

    Primaryoocyte:23pairs.Secondaryoocyte:23.Ootid:23.Follicle:23pairs.

  • 10. Whatiscorpusluteum.Howdoseitfunctionsasendocrinegland?

    Ans.Afterovulation,thegraffianfollicleruptures&formscorpusluteum.Corpusluteum

    functionsasendocrineglandsastheysecreteprogesterone&estrogeninlargequantities.

    11. Whereareleydigcellslocated?Whatdotheysecrete?

    Ans.Leydigcellsorinterstitialcellsarelocatedinbetweenthesominiferoustubules.Leydig

    cellssecretemalesexhormoneTESTOSTERONEwhichpromotesdevelopmentofaccessory

    glands&controlmalesecondarysexualcharacters.

    12. DrawwelllabeleddiagramofT.S.ofovary?

    Ans.

    13. Whytestesofhumanmalesareconsideredextraabdominal?Whatisthe

    significanceofthiscondition?

    Ans.Testisinhumanmalesarecalledextra-abdominalbecausetestisarelocatedoutsidethe

    abdominalcavityinapouchcalledscrotumwhichprovidesatemperature2-3oClowerthan

    bodytemperaturenecessaryforspermatogenesis.

  • 14. DrawadiagramoftheT.S.ofseminiferoustubuleoftestisofanadulthumanmale

    &labelanyfourpartsinit.

    Ans.

    15. Whatiscolustrum?Whatisitssignificancetonewbornbaby?

    Ans.Themilksecretedfrommammaryglandsjustafterbirthfor2or3daysiscalled

    colustrum.Itisrichinproteins&lowinfats.ItalsocontainsantibodyIgAwhichprovides

    immunitytonewborninfant.

  • 3MarksQuestions

    1. Mentionthenameandroleofhormoneswhichareinvolvedinregulationofgamete

    formationinhumanmale.

    Ans.GnRH:Stimulatesadenophysistosecretegonadotrophins.

    GSH:StimulatesSertolicellstosecretefactorswhilehelpinspermatogenesis.

    ICSH:Stimulatesinterstitialcellstosecretetestosterone.

    2. Threeofthestepsofneuroendocrinemechanisminrespectofparturitionare

    mentionedbelow.

    Writethemissingstepsinpropersequence.

    (a) Signalsoriginatefromfullydevelopedfoetusandplacenta.

    (b) ______________________________.

    (c) ______________________________.

    (d) Oxytocincausesstronguterinecontraction

    (e) Uterinecontractionstimulatesfurthersecretionofoxytocin.

    (f) ______________________________.

    Ans.(b)Foetalejectionreflex

    (c) Thereflextriggersreleaseofoxytocin

    (f) Expulsionofthebabyoutthroughbirthcanal.

  • 3. Theeventsofthemenstrualcyclearerepresentedbelow.Answerthefollowing

    questions.

    (i) StatethelevelsofFSH,LHandProgesteronesimplybymentioninghighorlow

    around13thand14thdayand21stto23rdday.

    (ii) Inwhichoftheabovementionedphasesdoeseggtraveltofallopiantube?

    (iii) Whythereisnomensurationafterfertilisation?

    Ans.(i)13-14thday21st-23rdday

    FSH-HighLow

    LH-HighLow

    Progesterone-LowHigh

    (ii) Endoffollicularorproliferativephase.

    (iii)Menstruationdoesnotoccurduringpregnancyuponfertilizationduetohighlevelof

    progestenonesecretedbypersistingcorpusluteumandPlacenta.

    4. (a)Readthegraphgivenbelow.Correlatetheovarianeventsthattakeplaceinthe

    humanfemaleaccordingtothelevelofthepituitaryhormoneduringthefollowingday.

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  • (i) 10th-14thdays(ii)14th-15thdays

    (iii) 16th-23thdays(iv)25th-29thdays

    (Iftheovumisnotfertilised)

    (b) Whataretheuterineeventsthatfollowbeyond29thdayiftheovumisnot

    fertilised?

    Ans.(a)(i)GonadotropinsandFSHincreases

    (ii) LHattainspeaklevelbutFSHdecreases

    (iii) LHandFSHleveldecreases

    (iv) LHremainslowandFSHincreases.

    (b) After29thdaythereisamentrualflowinvolvingdischargeofbloodandcastoff

    endometriumlining.

    5. T.S.ofmammaliantestisrevealingseminiferoustubulesshowdifferenttypesofcell.

    (i) Namethetwotypesofcellsofgerminalepithelium.

    (ii) Nameofcellsscatteredinconnectivetissueandlyingbetweenseminiferous

    tubules.

    Differentiatebetweenthemonthebasisoftheirfunctions.

  • Ans.(i)Germinalepitheliumhavetwotypesofcell.1.Spermatogonium.2.Sertolicells

    (ii) LeydigcellsorInterstitialcells.

    Functions

    Spermatogoniumundergoesmeioticdivisionleadingtospermformation.

    Sertolicell:Nourishesgermcells

    Leydigcell:SynthesiseandSecretehormoneandrogen.

    6. Whatarethevariousmaleaccessoryglands?Givetheirfunction.

    Ans.Themaleaccessoryglandsincludepairedseminalvesicles,aprostrateglandandpaired

    bulbourethralglands.

    Theseglandssecreteseminalplasmarichinfructose,calciumandcertainenzymes.

    Secretionsofbulbourethralglandshelpinlubricationofthepenis.

    7. Explainthemenstrualcyclewithadiagram.

    Ans.Menstrualcyclehasthreephases:menstrual,proliferativeandsecretory.

    a) MenstrualPhase:Thephaselastsfor3-5daysinhumanfemalesandduringthisperiodthe

    endometrialliningoftheuterusiscastoffandisslowlypassedoutfromvaginaasamixture

    ofblood.

    b) ProliferativeorFollicularPhase:Itlastsfor11daysbetween6thto16thdayofthecycle.

    DuringthisphaseoneovarianfollicleischangedintoGraafianfollicleandtheendometrial

    layerisrebuiltalongwithrepairoftherupturedbloodvessels.Estrogenincreases.Itends

    withovulation.

    c) SecretoryPhase:Itlastsfor12daysbetween17-28days.TheGraafianfollicleisconverted

    toCorpusLuteum.Theendometriumgrowsandthickensfurther.Progesteroneincreases.It

    endwiththeconversionofcorpusluteumtocorpusalbic

  • 8. Differentiatebetweenspermatogenesisandoogenesis.

    Ans.

    Spermatogenesis Oogenesis

    1. Itoccursinsidethetestes. 1. Itoccursinsidetheovary.

    2. Allthestagesarecompletedinsidethe

    testes.

    2. Majorityoccursinsidetheovarybutlast

    stagesoccurintheoviduct.

    3. Spermatogoniadevelopfromthe

    germinalepitheliumlininginthe

    seminiferoustubules.

    3. Oogoniadevelopfromthegerminal

    epitheliumoverlyingtheovary.

    4. Allspermatogoniagiveriseto

    spermatocytes.4. Onlyfewoogoniagiverisetooocytes.

    5. Primaryspermatocytesdividebymeiosis5. PrimaryoocyteundergoesmeiosisIto

    giverisetoonesecondaryoocyteanda

  • Itogiverisetotwosecondaryspematocytes polarbody.

    6. Secondaryspermatocytedividesby

    meiosisIItogiverisetotwospermatids.

    6. SecondaryoocytedividesbymeiosisIIto

    formtheovumandthesecondpolarbody.

    7. Eachspermatiddifferentiatesinto

    spermatozoanorsperm.

    7. Nodifferentiationisrequiredafter

    meiosisII.

    8. Thespermsformedaremotile. 8. Theovumoreggisnon-motile.

    9. ‘Afertilizedeggistheblueprintoffuturedevelopment’.Explain

    Ans.Thespermcarriesthegeneticinformationfromthefatherinformof23chromosomes

    (includingthemalesexchromosomeXorY)whiletheeggbearsthegeneticinformation

    fromthemother(includingthefemalesexchromosomeX).Thusduringfertilizationthe

    fusionofthemaleandthefemalegametesproducenewgeneticcombinationwhich

    introducesvariationintheprogeny.Thezygoteorthefertilizedeggcontainthegenetic

    informationwhichaccordinglycontrolsthedevelopmentoftheembryo.

    10. Brieflydescribethestagesofspermatogenesisinhuman?

    Ans.Spermatogenesisconsistsoftwophases:-

    I. FORMATIDNOFSPERMATIDS:-Itfurtherconsistof3phases

    1. Multiplicationphase:-undifferentiatedgermcellsundergorepeateddivisiontoproduce

    spermmothercellorspermatogonia.

    2. Growthphase:-Spermatogoniaincreaseinvolume&isnowcalledPRIMARY

    SPERMATOCYTES.

    3. Maturationphase:-primaryspermatocyteundergoesmeiosisItoproducesmallsize

    haploidsecondaryspermatocytesecondaryspermatocytedividesbymeiosis–II&forms

    haploidSpermatids.

    II.FORMATIONOFSPERMS:-Thetramsformationordifferentiationofspermatidsinto

    spermatozoaorspermiscalledspermiogenesis&occursundertheinfluenceofFSH

  • 11. Describethehormonalcontrolofhumanmalereproductionsystemwiththehelpof

    aflowchart&highlighttheinhibitory&stimulatorydirectionsinit?

    Ans.i)SpermatogenesisisinitiatedduetoanincreaseinthesecretionofGonadotropin

    releasinghormonefromhypothalamusattheageofpuberty.

    1. TheincreasedlevelsofGnRHactonanteriorpituitary&stimulatethesecretionoftwo

    gonadotropinsi-e.leuteinizinghormone(LH)&folliclestimulatinghormone(FSH)

    2. LHactsonleydigcells&stimulatethemtosecretetestosterone

    3. FSHactsonsertolicells&stimulatesecretionofsomefactorshelpinspermiogenesis

  • 12. Aspermhasjustfertilizedahumanegginthefallopiantube.Tracetheeventsthat

    thefertilizedeggswillundergoesuptoimplantationofblastocystintheuterus.

    Ans.1.CLEAVAGE:-Fertilizedeggstartsdividinglayspecificmitoticdivisionscalled

    cleavage.Thezygotesundergoesmitoticdivisionintheisthmusofoviducttoformdaughter

    cellthecellsformedasaresultofcleavagecalledblastomere

    2. BLASTOCYST:-3-4daysafterfertilization,themorulatwinsintolargemassofcellscalled

    blastocystOuterperipheralcellsenlarge&flattenfurther&formtrophoblast.Trophoblast

    cellssecretesafluidintointerior&formacavitycalledblastocoel.Theembryonicstagewith

    blastocoelsiscalledblastula.

  • 13. Whereoogenesisdoestakesplace.Describethestagesofthisprocess?

    Ans.Theprocessofformation&maturationofovumiscalledoogenesis.Ittakesplacein

    ovary&isinitiatedduringembryonicdevelopmentoffemalefoetus.Itconsistsof3phases:--

    1. Multiplicationphase:-Theprimordialgermcellsdividebymeiosistoproduceoogonia.

    Theseoogoniadividelayrepeatedmitoticdivisionsformingclusters.Ineachclusteronly

    oneofthementersintogrowthphase&iscalledprimaryoocyte.

    2. Growthphase:-Growthphaseoccursonlyafterattainmentofpuberty.Itinvolves–

    increaseinsizeofoocytetomanyfolds&synthesisofyou.

    3. Maturationphase:-Thefirstdivisionismeioticasaresulttwohaploid(n)cellsare

    produced.Inthisdivision,cytobinesisisunequal,largedaughtercellwithalmostall

    cytoplasmiscalledsecondaryoocyte&smallermewithlesscytoplasmiscalledpolar

    body.Thesecondaryoocytethenundergoessecondmeioticdivisiontoformanovum&

    secondpolarbody.

  • 5MarksQuestions

    1.

  • Ans.(i)’D’Spermatids=undergospermiogenesis

    (ii) ‘A’=Spermatogonium;B=Primaryspermatocyte

    (iii) ‘B’=DiploidE=Haploid

    (iv) ‘F’=Sertolicells-Nutritiontogermcells

    (v) MitosisinCell‘A’,Meiosisincell‘B’

    2. Explainthedevelopmentofhumanembryowithdiagrams.

    Ans.TheFusionofthespermandtheegginhumansresultintoformationofthediploid

    structurecalledzygote.Thezygotestartsdividingmitoticallyasitmovesthroughtheoviduct

    intotheuterustoform2,4,8,16daughtercellscalledblastomeres.Thestageiscalledmorula.

    TheMoruladividesfurtheranddifferentiatesintoblastocysts.Theouterlayerofblastomeres

    calledtrophoblastgetsattachedtotheendometriallayeroftheuterus.

    Theuterinewalldividesandenclosestheblastocystsandthisisreferredtoasimplantation.

    Theinnerlayerofblastomeresintheblastocystsgivesrisetotheembryo.

  • 3. Whatismenstruation?WhatarethespecificactionsofFSH,LH,estrogen&

    progesteroneinmenstrualcycle?

    Ans.Duringmenstrualphaseofmenstrualcyclewhichstartson28thdaytheendometrial

    liningoffemalegenitaltractbreakdownduetolackofprogesteroneAsaresultbleeding

    occurs.Thismonthlyflowofbloodiscallermenstruation.

    Duringmenstrualcycles,thevariouschangesoccursintheovaryundertheinfluenceof

    varioushormones:-

    1. Menstrualphase:-ThelevelsofhormonesLH,FDHestrogen&progesteroneisveryless

    whichresultsinbreakdownofendometrialliningofuterus.

    2. Follicularphase:-Inthisphase,thelevelsofpituitaryhormonesFSH&LHincreases

    whichcausesovarianhormoneestrogentorelease,.FSHcontrolsthefollicularphase,it

    stimulatesthegrowthoffollicles.BothFSH&LHreachtheirpeaklevelinmiddleofcycle

    (14thday)

    3. OVULATORYPHASE:-ThelevelofLHhormonesreachesitspeak(calledLHswing)

    inducestherupturesofmatureGraffianfollicle&therebyreleaseofovum

    4. Lutealphase:-TheLH&FSHhormonesbeginstodecline.Afterovulation,thefollicle

    becomestoruptures&istransformedintocorpusLuteumwhichsecreteslargequantities

    ofprogesterone

  • 4. Awomanhasconceived&implantationhasoccurredwithinheruterus.Discussthe

    sequenceofchangesuptoparturitionwhichwilltakeplacewithinherbodyunderthe

    influenceofvarioushormones.

    Ans.Thefollowingchangestakesplaceinthebodyofwomenafterimplantation:-

  • 1. Thetrophoblastdifferentiatesintotwolayersouterlayersecretesenzymestodissolvethe

    endometriumofuterus.

    2. Theinnerlayergrowsoutasfinger–likeprojectionscalledchorionicvilliintouterine

    stoma.Thechorionicvilli&theuterinetissuebecomeinterdigitatedtoformstructural&

    functionalunitcalledplacenta.

    3. PlacentasecreteshormoneslikeHCG,HPL,estrogen&progesteronethatarenecessaryto

    maintainpregnancy

    4. Umbilicalcord,thestructurethatconnectstheplacentawiththefoetusisformed.

    5. Simultaneously,innercellmassdifferentiatesintoouterlayercalledectoderm&inner

    layercalledendoderm.&amiddlelayercalledmesodermappearsbetweenectoderm&

    endoderm.

    6. Theprimarygermlayersgiverisetoallthetissues&organsoftheadultse.g.afterone

    monthheartisformed&aftersecondmonthdigits&limbsareformed.

    7. Bytheendofninthmonthofpregnancy,foetusiscompletelydeveloped&isreadyfor

    delivery.

    8. Duringparturition,ovarysecretesahormonecalledrelaxinthatfacilitatesparturition

    whichsoftenstheconnectivetissue.Mildcontractioncalledfoetalejectionreflexis

    induced.Thistriggersreleaseofoxytocinfromposteriorpituitary.Oxytocininduces

    strongerleadstoexpulsionofbabyfromuterus,throughbirthcanal.

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