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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