CBSEClass11BiologyImportantQuestions

Chapter17

BreathingandExchangeofGases

1MarksQuestions

1.Definepartialpressureofagas.

Ans.Pressurecontributedbyanindividualgasinamixtureofgasesiscalledpartial

pressureofgasanditisrepresentedasPO2forO2andPCO2forCO2.

2.Nametheotherpigmentswhicharepresentinanimalsbesideshaemoglobin.

Ans.Haemocyaninandhaemoerythrin.

3.Whatisthedifferencebetweenalveolarairandinspiredair?

Ans.Alveolarair–Theairpresentinthealveoli.

Inspiredair–Theamountofairinspiredatatime.

4.Definevitalcapacity.

Ans.VitalCapacityisthevolumeofairbreathedoutbyamaximumforcefulexpiration.

5.WhatistheroleofcarbonicanhydraseinRBC’s?

Ans.About70%ofCO2reactswithwatertoformcarbonicacidinRBCsinthepresenceof

enzymecarbonicanhydrase.CO2+H2O H2CO3

6.Whatiscarbaminohaemoglobin?

Ans.CarbaminohaemoglobinisformedwhenCO2combineswithglobinisreduced

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haemoglobin.

7.Nametheplacewhereactualexchangeofgasestakesplaceininsects.

Ans.Tracheoles.

8.WhatisthepercentageofO2ininspired&expiredair?

Ans.Inspiredairhas21%O2andexpiredairhas16%O2.

9.Whatistheutilityofchlorideshift?

Ans.Itmaintainstheionicbalanceandelectrochemicalneutrality.

10.Nametheorganinhumanrespiratorysystemwhichproducessound.

Ans.Larynx(Soundbox)

11.Howmanyoxygenmoleculescanbecarriedoutbyonehemoglobinmolecule.

Ans.Fourmolecules

12.Givethenameandfunctionofafluidfilleddoublemembranouslayer

whichsurroundsthelungs.

Ans.Fleuron.Itreducesthefrictionandkeepsthetwopleuratogetherandthelungs

inflated.

13.Whichorganofourrespiratorysystemactsasprimarysiteofexchangeofgases?

Ans.AlveoliofLungs.

14.Cigarettesmokingcausesemphysema.Givereason.

Ans.Cigarettesmokingdamagesalveolarwallsduetoalveolarsacsremainingfilledwithair

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leadingtodecreasedrespiratorysurfacefore

15.Nametheprincipleofexchangeofgases.

Ans.Diffusion.

16.Whatistheroleofoxyhaernoglobinafterreleasingmolecularoxygeninthe

Ans.AminogroupofrefucedhoemoglobincombineswithCO2forming

carbaminohaemoglobintotransportCO2.

17. Namethemuseleswhichfacilitatebreathing.

Ans.Externalandinternalintercostalsmuscles,situatedbetweenribs.

18.Howistheentryoffoodpivotedintherespiratorytract?

Ans.Ans.Duringswallowingacartilaginousflaplikestructurecalledepiglottiscoversthe

glottisandpreventstheentryoffoodintorespiratorytract.

19. About97%ofO2istransportedbyRBCsintheblood.Howdoestheremaining3%of

O2transported?

Ans.Insimplesolutionformthroughplasma.

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CBSEClass12Biology

ImportantQuestions

Chapter17

BreathingandExchangeofGases

2MarksQuestions

1.Giveroleofintercoastalsmusclesinrespiration.

Ans.Thecontractionoftheexternalintercoastalsmuscles&diaphragmincreasesthe

volumeofthethoraciccavitylowersthepressureinthelungs.Tofillupthegap,thefreshair

reachestothelungsresultingintheinspiration.

Therelaxationoftheinspiratorymusclesdecreasesthevolumeofthethoraciccavityand

subsequently,pressureinthelungsincrease.Toequalizethispressure,theairfromthe

lungsrushesoutthroughtherespiratorypassagetobringaboutexpiration.

2.ExplainErythrocytescancarryoutanaerobicmetabolismonly.

Ans.Erythrocyteslackmitochondriaandrespiratoryenzymestoperformtheprocessof

aerobicrespiration.Therefore,theyundergoaerobicrespirationtocarryoutanaerobic

metabolismonly.

3.Describehowourbraingetsacontinuoussupplyofoxygenformtheatmosphere.

Ans.Passageofairwhichcontainsoxygen:

Inhalationoffreshair→trachea→bronchi→lungs→alveoli→diffusionofO2intoblood

(RBC)→formationofoxygemoglobin→someinplasma→pulmonaryvein→carryittoheart→ leftauricle→toventricle→Dorsalaorta→Carotidarterytothebraindissociationofoxyhaemoglobin,O2suppliedtothetissue,partialpressureofO2facilitatesdiffusion.

4.Whatischlorideshift?Explain.

Ans.ThediffusionofchlorideionsfrombloodplasmaintoRBS’sisknownaschlorideshift.

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a) OccursfromplasmatoRBC’sinhumanbody.

b) Itmaintainsionicbalanceandelectrochemicalneutrality.

5.Explainbrieflythefirststepisrespiration?

Ans.Firststepinrespirationiscalledbreathing.Inbreathingatmosphericairistakeninby

inspirationandalveolarairisreleasedoutbyexpiration.TheexchangeofO2andCO2

betweendeoxygenatedbloodandalveoli,transportofgasesthroughoutbodybyblood,

exchangeofO2andCO2betweentheoxygenatedbloodandtissuesandutilizationofO2by

thecellsaretheotherstepsinvolvedinit.

6.Writeanoteonbronchitisanditsprevention.

Ans.Itis“inflammationofthebronchiandischaracterizedbyhypertrophyhyperplasia

seromucousglandsandgobletcellsliningthebronchi”

Symptomsarecoughingwiththickgreenish-yellowsputum.Itshowsinfection,thatexcessive

secretionofmucus.Itiscausedbypollutantsaswellasthecigarettesmoking.Preventionof

Bronchitis–

1) Avoidingexposuretoallergens.

2) Treatmentinvolvesantibiotictheory&bronchodilatordugs,etc.

7.Whatisthedifferencebetweencarbaminohaemoglobinandoxyhaemoglobin.

Ans.

Oxyhaemoglobin Carbominohaemoglobin

1.

Itisformedbythecombinationof

oxygenwiththeFe2+partof

haemoglobin.

Itisformedbythecombinationofcarbon

dioxidewiththeamineradicalof

haemoglobin.

ItformationoccursonthealveolarItsformationoccursinthetissues.

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2. surface.

8.Whatisfunctionalresidualcapacity?

Ans.Whenapersoninhalesandexhalesinanormalway,thevolumeairthatremainsinthe

lungsisknownasfunctionalresidualcapacity(FRC).Itincludestheresidualvolumeand

expiratoryreservevolume,i.e,FRC=RV+ERV.

9.DescribethetransportofO2andCO2?

Ans.O2istransportedasoxyhaemoglobin.Inthealveolioflungs(PO2ishigher),O2gets

boundtohemoglobinthatdissociatesattissueswherePO2andH+concentrationarehigh.

Approx70%CO2transportedasbicarbonate(HCO3-)withthehelpoftheenzymecarbonic

anhydrase,20-25%CO2iscarriedbyhaemoglobinascarbaminohamoglobin.IntissuesPCO2

ishighitsgetsboundtobloodbutinalveoliwherePCO2islowandPO2ishigh,thisremoved

fromblood.

10. Nametheorgansofrespirationinthefollowingorganisms.

a) Flatwormsb)Birdsc)Frogd)Cockroach

Ans.a)Bodysurfaceb)lungsc)skinandlungsd)Networkoftrachea

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CBSEClass12Biology

ImportantQuestions

Chapter17

BreathingandExchangeofGases

3MarksQuestions

1.Whatishypoxia,artificialhypoxia&Anaemichypoxia?

Ans.Hypoxia–Itisaconditionofoxygenshortageinthetissues.Itis2kinds–artificial

hypoxiaandanaemichypoxia.

Artificialhypoxia–Itistheresultofshortageofairover2400maltitudes.Themountain

sicknessiscausedbyheadache,dizziness,nausea,vomiting,mentalfatigueandbreathless

messetc.

Anaemichypoxia–resultsduetoreducedO2capacityofbloodduetolesscontentofHbor

carbonmonoxidepoisoning.

2.Howisrespirationregulated?

Ans.Respiratorycentrelocatedinfloorofthemedullaoblongataofthebraincontrols

respiration.Thecentreisbilateralanditstwohalveswhichareconnectedtogetherby

commissuralneurons.Thesidesofthiscentreareconnectedwithmotorrespiratoryneuron.

Thenervecellsofthecentreareconnectedwiththebreathingapparatusformingareflex

arc.Thesenervecellsaresecretivetochemicalcompositionofblood.Halfoftherespiratory

centreisaninspiratorycentreandexpiratorycentre.Itisbelievedthattheinspiratory

centreworkinnormalbreathingandexpiratorycentreduringotherconditionslike

coughing,sneezingandlaughing.Thesetwocenterscontroltheentirebreathinginmanwith

hisknowingaboutit.Dorsalrespiratorygroup,ventralrespiratorygroupandpneumoptaxic

groupsactasrespirationcentersinthebrain.

Neumotaxiccentreislocateddorsallyinupperpons.Ittransmitssignalstoinspiratoryarea.

Itcontrolstheswitchoffpointofinspiration.

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3.Differentiatebetweenvitallungcapacityandtotallungcapacity.

Ans.

VitalCapacity(VC) TotallungCapacity.(CT2C)

1.Sumtotaloftidalvolume,expiratory

reserveandinspiratoryreservevolume.

Sumtotalofvitalcapacityandresidual

volume.

2. VC=Vt+ERV+IRV TLC=VC+RV

3. Valueis3500-4500ml. Valueis5000–6000ml

4.

Representsmaximumamountofairthata

personcanexpelafterfillingthelungsto

themaximum.

Representsmaximumtotalamountof

airwhichcanbepresentinlungsafter

maximuminspiratoryeffort.

4.Explainthemechanismofbreathinginhumans.

Ans.Themechanismofbreathinginhumaninvolvesbreathinginofairinthelungsand

breathingoutofairfromlungsthoraciccavity.Theformiscalledinspirationandlater

expiration.Thelungsarelocatedintheclosedthoraciccavity.Amuscularpartitioncalled

diaphragmseparatesthethoraciccavityfromtheabdominalcavity.

Duringinspirationthediaphragmisloweredduetocontractionintercostalsmuscle.This

resultintotheincreaseofvolumeofthoraxcausingfallofairpressureinthethoraciccavity

lowersthepressureinthelungsandtheairrushesfromoutsideintolungsthroughexternal

nares,trachea&bronchi.

Duringexpirationthediaphragmmoveupwardandthelateralthoracicwallsmoveinwards

duetotherelaxationofmusclesofdiaphragmandtheintercoastalsmuscles.Thisdecrease

thevolumeofthoraxandthepressureinsidethethoraxandlungsisincreasedwhichresults

intheexpulsionofsomeofairfromthelungstotheatmosphereoutsidethebody.

5.Defineoxygendissociationcurve?Whyithassigmoidalpattern?

Ans.TherelationshipbetweenO2tensionanditsabsorptionbyhaemoglobinproducesa

graphcalledoxygendissociationcurve(O2equilibriumcurve).Atabout100mmHgO2

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tensionHbis98%saturated(completeformationofhaemoglobin).Asitfalls,thesaturation

ofHbdecreasesslowly.WhenO2tensionisabout40mmHg,oxyhaemoglobindissociatesand

O2isavailabletothetissues.

TheO2getsboundtoHbinlungsurfaceanditgetsdissociatedattissues.

6.Whatistheroleofcarbonicanhydrase?Showbyseriesofreactionshowcarbonic

anhydrasestartsthereactionsleadingtotheformationofhemoglobinicacid?

Ans.CarbonicAnhydrate:CO2reactswithwaterinpresenceofcarbonicanhydrasein

erythrocytes,Carbonicacid(H2CO3)isdissociatedintohydrogen(H+)andbicarbonate

(HCO3-)ions).Oxyhaemoglobin(HbO2)ofRBC’sisweaklyacidicandremaininassociation

withK+ionsasKHbO2.H+ionscombinewithhaemoglobin.Bricarbonateionsdiffuseout

intoplasmaandcombinewithhaemoglobintofromhaemoglobinicacid(H.Hb)

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CBSEClass12Biology

ImportantQuestions

Chapter17

BreathingandExchangeofGases

5MarksQuestions

1.DescribetransportmechanismofCO2.

Ans.TransportofCO2intheblood.

(i) Inthedissolvedform

About5–7%ofcarbon–dioxideistransportedindissolvedformintheplasmaofblood.

(ii) Intheformofbicarbonate.

Theremainingpartofcarbondioxideenterstheerythrocytes,whereitreactswiththewater

toformcarbonicacid(H2CO3);thisreactioniscatalysedbycarbonicanhydrase.

OCarbonicacidimmediatelydissociatesintohydrogenions(H+)andbicarbonate(HCO3-)

OTheseH+ionscombinewithhaemoglobin,aftertheoxyglobin(KHbO2)dissociatesto

liberatetheoxygen;asaresulthaemoglobinicacid(H.Hb)isformed.

OThemajorityofbicarbonateions(HCO-3)diffusesoutoftheerythrocytesintotheplasma,

followingaconcentrationgradient.

OInresponse,chlorideions(Cl-)diffusefromtheplasmaintotheerythrocytes(Chloride

shift)andelectricalneutralityismaintained.

OThechlorideionscombinewithpotassiumtoformpotassiumchloride.

OIntheplasmathebicarbonateionscombinewithsodiumandtransportedassodium

bicarbonate(NaHCO3)

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ONearly70%ofthecarbondioxideistransportedinthisform.

(iii) Intheformofcarbaminohaemoglobin

OSameamountofCO2reactswiththeamineradicals(NH2+)ofhaenoglobinandform

carbaminohaemoglobin(HbCO2)molecule.

OAbout23%ofcarbon–dioxideistransportedinthisform.

2. Describeinbrieftherespiratoryorgansofman.

Ans.Thefollowingarethemainrespiratoryorgans:-

1)Nostrils–Thesearethepairedopeningssituatedattheanteriorandposteriorendsofthe

nasalchambers.Theyarelinedupwithciliatedepitheliumandmucouscells.Theseprevent

theentranceofdustintolungsandhelpinwarmingandmoisteningtheair.Thenasal

chamberopensinteriorlybyexternalnostrilandposteriorinternalnostrilintothepharynx.

2)Larynx–Itissituatedattheanteriorpartoftracheaandcommunicateswiththepharynx.

Theglottisisprotectedbyastiffcartilagecalledepiglottis.Thelarynxcontainspairsofvocal

cordswhichsetintovibrationswhentheairentersintoitandproducesthesound.

3)Trachea–Itisalongringedtube.Itissupportedc–shapedelasticcartilaginouringsto

preventitscollapsing.Itislinedinternallywithmucousmembranetoholdthedustparticles,

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bacteriaandotherforeignbodies.Italsowarmstheair.

4)Bronchi–Insidethethorax,thetracheabifurcatesintotwobranchyandeachofwhich

entersintoonelung.Ineachlung,thebronchusagainredividesintonumeroussmall

branchesknownasbronchioles.Thesebronchiolesfurtherdivideatitsendstoform

respiratorybronchioles.

5)Lungs–Therearetwolargebag-likespongystructureswhicharethemainrespiratory

organs.Theseareenclosedbydoublepleuralmembranes.Thelungsaredividedexternally

bylobes.Therightlungconsistsoffourlobesandleftbytwolobes.Insidethelungs,the

respiratorybronchiolesgiverisetoalveolarducts,alveolarsacandfinallyalveoli.Eachlung

containsmillionsofalveoli.Eachalveolusisexceptionallythinwalled.Itswallsarehighly

permeableandrichlysuppliedwithbloodcapillaries.

Thebloodissuppliedtothelungsbyapairofpulmonaryarteries.Thesebringbloodwhich

poorinoxygen&richinCO2.Theexchangeofgasesoccursinthealveoliofthelungs.The

oxygenatedbloodfromalveolarcapillariesiscalledbypairofpulmonaryveintobe

conveyedtotheheart.

3. Explainhowourheartmusclesgetacontinuoussupplyofatmosphericoxygen.

Ans.Wheninspirationoccurs,theO2istakenintolungs.O2mixeswithairalreadypresent

inalveoliandbecomesalveolarair,whosePO2is100mHg.

AsPO2ofbloodinthevesselsis40mmHgoxygendiffersintobloodvesselsfromalveoliand

theoxyhaemoglobinisformedwhenoxygencombineslooselywiththeFe++ionsof

haemoglobin.

Oxygenatedbloodfromthelungsreachestheleftauriclethroughpulmonaryvein;toleft

ventricleispumpedatthroughaortaalso.

Thebranchsupplyingbloodtoheartmusclesiscoronaryartery.Inheartmuscles,asthePO2

islowerthanthatofthebloodinthebranchesofcoronaryartery,oxyhaemoglobin

dissociatesandreleasesO2tocardiacmuscles.

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