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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