CBSE Class–12 Subject Chemistry NCERT Exemplar Solutions ...
Transcript of CBSE Class–12 Subject Chemistry NCERT Exemplar Solutions ...
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CBSEClass–12SubjectChemistry
NCERTExemplarSolutions
Chapter14
Biomolecules
MultipleChoiceQuestions(Type-I)
1.Glycogenisabranchedchainpolymerofα-D-glucoseunitsinwhichchainisformed
byC1—C4glycosidiclinkagewhereasbranchingoccursbytheformationofC1-C6
glycosidiclinkage.Structureofglycogenissimilarto__________.
(i)Amylose
(ii)Amylopectin
(iii)Cellulose
(iv)Glucose
Ans.(ii)Amylopectin
Explanation:Polysaccharidescontainalargenumberofmonosaccharideunitsjoined
togetherbyglycosidiclinkages.Thesearethemostcommonlyencounteredcarbohydratesin
nature.Amylopectinisinsolubleinwaterandconstitutesabout80-85%ofstarch.Itisa
branchedchainpolymerofalpha-D-glucoseunitsinwhichchainisformedbyC1-C4
glycosidiclinkagewhereasbranchingoccursbyC1-C6glycosidiclinkage.
2.Whichofthefollowingpolymerisstoredintheliverofanimals?
(i)Amylose
(ii)Cellulose
(iii)Amylopectin
(iv)Glycogen
Ans.(iv)Glycogen
Explanation:Thecarbohydratesarestoredinanimalbodyasglycogen.Itisalsoknownas
animalstarchbecauseitsstructureissimilartoamylopectinandisrathermorehighly
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branched.Itispresentinliver,musclesandbrain.
3.Sucrose(canesugar)isadisaccharide.Onemoleculeofsucroseonhydrolysisgives
_________.
(i)2moleculesofglucose
(ii)2moleculesofglucose+1moleculeoffructose
(iii)1moleculeofglucose+1moleculeoffructose
(iv)2moleculesoffructose
Ans.(iii)1moleculeofglucose+1moleculeoffructose
Explanation:Oneofthecommondisaccharidesissucrosewhichonhydrolysisgives
equimolarmixtureofD-(+)-glucoseandD-(-)fructose.
4.Whichofthefollowingpairsrepresentsanomers?
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Ans.(iii)
Explanation:Thetwocyclichemiacetalformsofglucosedifferonlyintheconfigurationof
thehydroxylgroupatCl,calledanomericcarbon(thealdehydecarbonbeforecyclisation).
Suchisomers,i.e.,alpha-formandbeta-form,arecalledanomers.
5.Proteinsarefoundtohavetwodifferenttypesofsecondarystructuresviz.α-helix
andβ-pleatedsheetstructure.α-helixstructureofproteinisstabilisedby:
(i)Peptidebonds
(ii)vanderWaalsforces
(iii)Hydrogenbonds
(iv)Dipole-dipoleinteractions
Ans.(iii)Hydrogenbonds
Explanation:α-helixandβ-pleatedsheetstructure:Thesestructuresariseduetothe
regularfoldingofthebackboneofthepolypeptidechainduetohydrogenbondingbetween
>C—Oand—NH—groupofthepeptidebond.
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-Helixisoneofthemostcommonwaysinwhichapolypeptidechainformsallpossible
hydrogenbondbytwistingintoaright-handedscrew(helix)withthe-NHgroupofeach
aminoacidresiduehydrogenbondedtothe ofanadjacentturnofthehelix.
6.Indisaccharides,ifthereducinggroupsofmonosaccharidesi.e.aldehydicorketonic
groupsarebonded,thesearenon-reducingsugars.Whichofthefollowingdisaccharide
isanon-reducingsugar?
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Ans.(ii)
Explanation:Oneofthecommondisaccharidesissucrosewhichonhydrolysisgives
equimolarmixtureofD-(+)-glucoseandD-(-)fructose.Thesetwomonosaccharidesareheld
togetherbyaglycosidiclinkagebetweenClof -glucoseandC2ofbeta-fructose.
Sincethereducinggroupsofglucoseandfructoseareinvolvedinglycosidicbondformation,
sucroseisanon-reducingsugar.
7.Whichofthefollowingacidsisavitamin?
(i)Asparticacid
(ii)Ascorbicacid
(iii)Adipicacid
(iv)Saccharicacid
Ans.(ii)Ascorbicacid
Explanation:VitaminCisalsoknownasAscorbicacid.
8.Dinucleotideisobtainedbyjoiningtwonucleotidestogetherbyphosphodiester
linkage.Betweenwhichcarbonatomsofpentosesugarsofnucleotidesarethese
linkagespresent?
(i)5′and3′
(ii)1′and5′
(iii)5′and5′
(iv)3′and3′
Ans.(i)5′and3′
Explanation:Nucleotidesarejoinedtogetherbyphosphodiesterlinkagebetween5’and3’
carbonatomsofthepentosesugar.
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9.Nucleicacidsarethepolymersof______________.
(i)Nucleosides
(ii)Nucleotides
(iii)Bases
(iv)Sugars
Ans.(ii)Nucleotides
Explanation:Nucleicacidsarelongchainpolymersofnucleotides,sotheyarealsocalled
polynucleotides.
10.Whichofthefollowingstatementsisnottrueaboutglucose?
(i)Itisanaldohexose.
(ii)OnheatingwithHIitformsn-hexane.
(iii)Itispresentinfuranoseform.
(iv)Itdoesnotgive2,4-DNPtest.
Ans.(iii)
Explanation:Fructoseispresentinfuranoseform.
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11.Eachpolypeptideinaproteinhasaminoacidslinkedwitheachotherinaspecific
sequence.Thissequenceofaminoacidsissaidtobe____________.
(i)primarystructureofproteins.
(ii)secondarystructureofproteins.
(iii)tertiarystructureofproteins.
(iv)quaternarystructureofproteins.
Ans.(i)primarystructureofproteins.
Explanation:Sequenceofaminoacidsissaidtobeprimarystructureofproteins.
12.DNAandRNAcontainfourbaseseach.Whichofthefollowingbasesisnotpresent
inRNA?
(i)Adenine
(ii)Uracil
(iii)Thymine
(iv)Cytosine
Ans.(iii)Thymine
Explanation:DNAcontainsfourbasesviz.adenine(A),guanine(G),cytosine(C)and
thymine(T).RNAalsocontainsfourbases;thefirstthreebasesaresameasinDNAbutthe
fourthoneisuracil(U).
13.WhichofthefollowingBgroupvitaminscanbestoredinourbody?
(i)VitaminB1
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(ii)VitaminB2
(iii)VitaminB6
(iv)VitaminB12
Ans.(iv)VitaminB12
Explanation:Watersolublevitaminsmustbesuppliedregularlyindietbecausetheyare
readilyexcretedinurineandcannotbestored(exceptvitaminB12)inourbody.
14.WhichofthefollowingbasesisnotpresentinDNA?
(i)Adenine
(ii)Thymine
(iii)Cytosine
(iv)Uracil
Ans.(iv)Uracil
Explanation:UracilispresentinRNAbutnotinDNA.
15.Threecyclicstructuresofmonosaccharidesaregivenbelowwhichoftheseare
anomers.
(i)IandII
(ii)IIandIII
(iii)IandIII
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(iv)IIIisanomerofIandII
Ans.(i)IandII
Explanation:Thisbehaviorcouldnotbeexplainedbytheopenchainstructure(I)for
glucose.Itwasproposedthatoneofthe—OHgroupsmayaddtothe—CHOgroupandform
acyclichemiacetalstructure.Itwasfoundthatglucoseformsasix-memberedringinwhich
—OHatC-5isinvolvedinringformation.Thisexplainstheabsenceof—CHOgroupandalso
existenceofglucoseintwoformsasshownbelow.
16.Whichofthefollowingreactionsofglucosecanbeexplainedonlybyitscyclic
structure?
(i)Glucoseformspentaacetate.
(ii)Glucosereactswithhydroxylaminetoformanoxime.
(iii)Pentaacetateofglucosedoesnotreactwithhydroxylamine.
(iv)Glucoseisoxidisedbynitricacidtogluconicacid.
Ans.(iii)Pentaacetateofglucosedoesnotreactwithhydroxylamine.
Explanation:Thepentaacetateofglucosedoesnotreactwithhydroxylamineindicatingthe
absenceoffree—CHOgroup.
17.OpticalrotationsofsomecompoundsalongwiththeirstructuresaregivenBelow.
WhichofthemhaveDconfiguration.
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(i)I,II,III
(ii)II,III
(iii)I,II
(iv)III
Ans.(i)I,II,III
Explanation:Allthosecompoundswhichcanbechemicallycorrelatedto(+)isomerof
glyceraldehydearesaidtohaveD-configurationwhereasthosewhichcanbecorrelatedto(-)
isomerofglyceraldehydearesaidtohaveL-configuration.
18.Structureofadisaccharideformedbyglucoseandfructoseisgivenbelow.Identify
anomericcarbonatomsinmonosaccharideunits.
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(i)‘a’carbonofglucoseand‘a’carbonoffructose.
(ii)‘a’carbonofglucoseand‘e’carbonoffructose.
(iii)‘a’carbonofglucoseand‘b’carbonoffructose.
(iv)‘f’carbonofglucoseand‘f’carbonoffructose.
Ans.(iii)‘a’carbonofglucoseand‘b’carbonoffructose.
Explanation:TwomonosaccharidesareheldtogetherbyaglycosidiclinkagebetweenClof
-glucoseandC2of -fructose.
19.Threestructuresaregivenbelowinwhichtwoglucoseunitsarelinked.Whichof
theselinkagesbetweenglucoseunitsarebetweenC1andC4andwhichlinkagesare
betweenC1andC6?
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(i)(A)isbetweenC1andC4,(B)and(C)arebetweenC1andC6
(ii)(A)and(B)arebetweenC1andC4,(C)isbetweenC1andC6
(iii)(A)and(C)arebetweenC1andC4,(B)isbetweenC1andC6
(iv)(A)and(C)arebetweenC1andC6,(B)isbetweenC1andC4
Ans.(iii)(A)and(C)arebetweenC1andC4,(B)isbetweenC1andC6
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CBSEClass–12SubjectChemistry
NCERTExemplarSolutions
Chapter14
Biomolecules
MultipleChoiceQuestions(Type-II)
Note:Inthefollowingquestionstwoormoreoptionsmaybecorrect.
20.Carbohydratesareclassifiedonthebasisoftheirbehaviouronhydrolysisandalso
asreducingornon-reducingsugar.Sucroseisa__________.
(i)monosaccharide
(ii)disaccharide
(iii)reducingsugar
(iv)non-reducingsugar
Ans.(ii),(iv)
Explanation:Oneofthecommondisaccharidesissucrosewhichonhydrolysisgives
equimolarmixtureofD-(+)-glucoseandD-(-)fructose.Thesetwomonosaccharidesareheld
togetherbyaglycosidiclinkagebetweenClof -glucoseandC2of -fructose.Sincethe
reducinggroupsofglucoseandfructoseareinvolvedinglycosidicbondformation,sucroseis
anon-reducingsugar.
21.Proteinscanbeclassifiedintotwotypesonthebasisoftheirmolecularshapei.e.,
fibrousproteinsandglobularproteins.Examplesofglobularproteinsare:
(i)Insulin
(ii)Keratin
(iii)Albumin
(iv)Myosin
Ans.(i),(iii)
Explanation:Globularproteins:Thisstructureresultswhenthechainsofpolypeptidescoil
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aroundtogiveasphericalshape.Theseareusuallysolubleinwater.Insulinandalbumins
arethecommonexamplesofglobularproteins.
22.Whichofthefollowingcarbohydratesarebranchedpolymerofglucose?
(i)Amylose
(ii)Amylopectin
(iii)Cellulose
(iv)Glycogen
Ans.(ii),(iv)
Explanation:Amylopectinisinsolubleinwaterandconstitutesabout80-85%ofstarch.Itis
abranchedchainpolymerof–D-glucoseunitsinwhichchainisformedbyCl-C4glycosidic
linkagewhereasbranchingoccursbyC1-C6glycosidiclinkage.Glycogen:Thecarbohydrates
arestoredinanimalbodyasglycogen.Itisalsoknownasanimalstarchbecauseitsstructure
issimilartoamylopectinandisrathermorehighlybranched.
23.Aminoacidsareclassifiedasacidic,basicorneutraldependingupontherelative
numberofaminoandcarboxylgroupsintheirmolecule.Whichofthefollowingare
acidic?
(i)
(ii)
(iii)H2N—CH2—CH2—CH2—COOH
(iv)
Ans.(ii),(iv)
Explanation:Aminoacidsareclassifiedasacidic,basicorneutraldependinguponthe
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relativenumberofaminoandcarboxylgroupsintheirmolecule.Equalnumberofamino
andcarboxylgroupsmakesitneutral;morenumberofaminothancarboxylgroupsmakesit
basicandmorecarboxylgroupascomparedtoaminogroupsmakesitacidic.
24.Lysine, is_______________.
(i)α-Aminoacid
(ii)Basicaminoacid
(iii)Aminoacidsynthesisedinbody
(iv)β-Aminoacid
Ans.(i),(ii)
25.Whichofthefollowingmonosaccharidesarepresentasfivememberedcyclic
structure(furanosestructure)?
(i)Ribose
(ii)Glucose
(iii)Fructose
(iv)Galactose
Ans.(i),(iii)
Explanation:Fructose:Italsoexistsintwocyclicformswhichareobtainedbytheaddition
of—OHatC5tothegroup.Thering,thusformedisafive-memberedringandisnamedas
furanosewithanalogytothecompoundfuran.Furanisafive-memberedcycliccompound
withoneoxygenandfourcarbonatoms.
26.Infibrousproteins,polypeptidechainsareheldtogetherby___________.
(i)vanderWaalsforces
(ii)disulphidelinkage
(iii)electrostaticforcesofattraction
(iv)hydrogenbonds
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Ans.(i),(ii)
Explanation:Infibrousproteins,mainforceswhichstabilizestructuresofproteinsare
disulphidelinkagesandvanderWaals.
27.Whichofthefollowingarepurinebases?
(i)Guanine
(ii)Adenine
(iii)Thymine
(iv)Uracil
Ans.(i),(ii)
28.Whichofthefollowingtermsarecorrectaboutenzyme?
(i)Proteins
(ii)Dinucleotides
(iii)Nucleicacids
(iv)Biocatalysts
Ans.(i),(iv)
Explanation:Lifeispossibleduetothecoordinationofvariouschemicalreactioninliving
organisms.Thisoccurswiththehelpofcertainbiocatalystscalledenzymes.Almostallthe
enzymesareglobularProtein.
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CBSEClass–12SubjectChemistry
NCERTExemplarSolutions
Chapter14
Biomolecules
ShortAnswerType
29.Namethesugarpresentinmilk.Howmanymonosaccharideunitsarepresentinit?
Whataresucholigosaccharidescalled?
Ans.Lactoseiscommonlyknownasmilksugarsincethisdisaccharideisfoundinmilk.Itis
composedofβ-D-galactoseandβ-D-glucose.ThelinkageisbetweenC1ofgalactoseandC4of
glucose.
30.Howdoyouexplainthepresenceofallthesixcarbonatomsinglucoseinastraight
chain?
Ans.OnprolongedheatingwithHI,glucosegivesn-hexane.
31.Innucleosideabaseisattachedat1′positionofsugarmoiety.Nucleotideisformed
bylinkingofphosphoricacidunittothesugarunitofnucleoside.Atwhichpositionof
sugarunitisthephosphoricacidlinkedinanucleosidetogiveanucleotide?
Ans.Phosphoricacidislinkedat5′-positionofsugarmoietyofnucleosidetogivea
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nucleotide.
32.Namethelinkageconnectingmonosaccharideunitsinpolysaccharides.
Ans.Glycosidiclinkage.
33.Underwhatconditionsglucoseisconvertedtogluconicandsaccharicacid?
Ans.Glucoseisconvertedtogluconicacidbybrominewaterandtosaccharicacidbyconc.
HNO3.
34.Monosaccharidescontaincarbonylgrouphenceareclassified,asaldoseorketose.
Thenumberofcarbonatomspresentinthemonosaccharidemoleculearealso
consideredforclassification.Inwhichclassofmonosaccharidewillyouplacefructose?
Ans.Fructoseisanimportantketohexose.Itisobtainedalongwithglucosebythehydrolysis
ofdisaccharide,sucrose.FructosealsohasthemolecularformulaC6H12O6andonthebasis
ofitsreactionsitwasfoundtocontainaketonicfunctionalgroupatcarbonnumber2and
sixcarbonsinstraightchainasinthecaseofglucose.
35.Theletters‘D’or‘L’beforethenameofastereoisomerofacompoundindicatethe
correlationofconfigurationofthatparticularstereoisomer.Thisreferstotheir
relationwithoneoftheisomersofglyceraldehyde.Predictwhetherthefollowing
compoundhas‘D’or‘L’configuration.
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Ans.Theletters‘D’or‘L’beforethenameofanycompoundindicatetherelative
configurationofaparticularstereoisomer.Thisreferstotheirrelationwithaparticular
isomerofglyceraldehydes.
D’beforethenameofglucoserepresentstheconfigurationwhereas‘(+)’represents
dextrorotatorynatureofthemolecule.Itmayberememberedthat‘D’and‘L’haveno
relationwiththeopticalactivityofthecompound.Forassigningtheconfigurationof
monosaccharides,itisthelowestasymmetriccarbonatomwhichiscompared.Thegiven
compoundhasL-configuration.
36.Aldopentosesnamedasriboseand2-deoxyribosearefoundinnucleicacids.Whatis
theirrelativeconfiguration?
Ans.configurationassignedisO.Thus,roboseisβ-D-riboseDeoxyriboseisβ-D-2-
deoxyribose.
37.Whichsugariscalledinvertsugar?Whyisitcalledso?
Ans.Sucroseisdextrorotatorybutafterhydrolysisgivesdextrorotatoryglucoseand
laevorotatoryfructose.Sincethelaevorotationoffructose ismorethan
dextrorotationofglucose ,themixtureislaevorotatory.Thus,hydrolysisofsucrose
bringsaboutachangeinthesignofrotation,fromdextro(+)tolaevo(-)andtheproductis
namedasinvertsugar.
38.Aminoacidscanbeclassifiedasα-,β-,γ-,δ-andsoondependingupontherelative
positionofaminogroupwithrespecttocarboxylgroup.Whichtypeofaminoacids
formpolypetidechaininproteins?
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Ans. -aminoacidsformpolypeptidechaininproteins.
39.α-Helixisasecondarystructureofproteinsformedbytwistingofpolypeptidechain
intorighthandedscrewlikestructures.Whichtypeofinteractionsare
responsibleformakingtheα-helixstructurestable?
Ans.In -helix,apolypeptidechainisstabilizedbytheformationofhydrogenbonds
between—NH—groupofaminoacidsinoneturnwiththe>C—Ogroupsofaminoacids
belongingtoadjacentturn.
40.Someenzymesarenamedafterthereaction,wheretheyareused.Whatnameis
giventotheclassofenzymeswhichcatalysetheoxidationofonesubstratewith
simultaneousreductionofanothersubstrate.
Ans.Oxidoreductaseisclassofenzymeswhichcatalysetheoxidationofonesubstratewith
simultaneousreductionofanothersubstrate.
41.Duringcurdlingofmilk,whathappenstosugarpresentinit?
Ans.Whenmilkiscurdeled,itssugargetoxidizetoformlacticacid.
42.Howdoyouexplainthepresenceoffive—OHgroupsinglucosemolecule?
Ans.Acetylationofglucosewithaceticanhydridegivesglucosepentaacetatewhichconfirms
thepresenceoffive—OHgroups.Sinceitexistsasastablecompound,five—OHgroups
shouldbeattachedtodifferentcarbonatoms.
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43.Whydoescompound(A)givenbelownotformanoxime?
Ans.Glucosepentaacetate(structureA)doesn’thaveafree—OHgroupatC1andsocan’tbe
convertedtotheopenchainformtogive—CHOgroupandhencedoesn’tformtheoxime.
44.WhymustvitaminCbesuppliedregularlyindiet?
Ans.VitaminCaresolubleinwater.Watersolublevitaminsmustbesuppliedregularlyin
dietbecausetheyarereadilyexcretedinurineandcannotbestoredinourbody.
45.Sucroseisdextrorotatorybutthemixtureobtainedafterhydrolysisis
laevorotatory.Explain.
Ans.Sucroseisdextrorotatorybutafterhydrolysisgivesdextrorotatoryglucoseand
laevorotatoryfructose.Sincethelaevorotationoffructose ismorethan
dextrorotationofglucose ,themixtureislaevorotatory.
46.Aminoacidsbehavelikesaltsratherthansimpleaminesorcarboxylicacids.
Explain.
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Ans.Aminoacidsbehavelikesaltsratherthansimpleaminesorcarboxylicacids.This
behaviourisduetothepresenceofbothacidic(carboxylgroup)andbasic(aminogroup)
groupsinthesamemolecule.Inaqueoussolution,thecarboxylgroupcanloseaprotonand
aminogroupcanacceptaproton,givingrisetoadipolarionknownaszwitterion.
47.Structuresofglycineandalaninearegivenbelow.Showthepeptidelinkagein
glycylalanine.
Ans.Inglycylalanine,carboxylgroupofglycinecombineswiththeaminogroupofalanine.
48.Proteinfoundinabiologicalsystemwithauniquethree-dimensionalstructureand
biologicalactivityiscalledanativeprotein.Whenaproteininitsnativeform,is
subjectedtoaphysicalchangelikechangeintemperatureorachemicalchangelike,
changeinpH,denaturationofproteintakesplace.Explainthecause.
Ans.Proteinfoundinabiologicalsystemwithauniquethree-dimensionalstructureand
biologicalactivityiscalledanativeprotein.Whenaproteininitsnativeform,issubjectedto
physicalchangelikechangeintemperatureorchemicalchangelikechangeinpH,the
hydrogenbondsaredisturbed.Duetothis,Globulesunfoldandhelixgetuncoiledand
proteinlosesitsbiologicalactivity.Thisiscalleddenaturationofprotein.
49.Activationenergyfortheacidcatalysedhydrolysisofsucroseis6.22kJmol-1,while
theactivationenergyisonly2.15kJmol–1whenhydrolysisiscatalysedbytheenzyme
sucrase.Explain.
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Ans.Enzymesareneededonlyinsmallquantitiesfortheprogressofareaction.Similarto
theactionofchemicalcatalysts,enzymesaresaidtoreducethemagnitudeofactivation
energy.Forexample,activationenergyforacidhydrolysisofsucroseis6.22kJmol-1,while
theactivationenergyisonly2.15kJmol-1whenhydrolysedbytheenzyme,sucrase.
50.Howdoyouexplainthepresenceofanaldehydicgroupinaglucosemolecule?
Ans.Glucosegetsoxidisedtosixcarboncarboxylicacid(gluconicacid)onreactionwitha
mildoxidisingagentlikebrominewater.Thisindicatesthatthecarbonylgroupispresentas
analdehydicgroup.
51.Whichmoietiesofnucleosidesareinvolvedintheformationofphosphodiester
linkagespresentindinucleotides?Whatdoestheworddiesterinthenameoflinkage
indicate?Whichacidisinvolvedintheformationofthislinkage?
Ans.Whennucleosideislinkedtophosphoricacidat5-positionofsugarmoiety,itformsa
nucleotide.Nucleotidesarejoinedtogetherbyphosphodiesterlinkbetween5’and3’carbon
atomsofthepentosesugar.
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Phosphericacidisinvolvedintheformationofthislinkage.
52.Whatareglycosidiclinkages?Inwhichtypeofbiomoleculesaretheypresent?
Ans.Thetwomonosaccharidesarejoinedtogetherbyanoxidelinkageformedbythelossof
awatermolecule.Suchalinkagebetweentwomonosaccharidesareheldtogetherbya
glycosidiclinkagebetweenC1of -glucoseandC2ofβ-fructose.Sincethereducinggroups
ofglucoseandfructoseareinvolvedinglycosidicbondformation,betweentwo
monosaccharideunitsthroughoxygenatomiscalledglycosidiclinkage.
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53.Whichmonosaccharideunitsarepresentinstarch,celluloseandglucoseandwhich
linkageslinktheseunits?
Ans.Instarchandglycogen,glycosidic -linkageispresent.Celluloseisastraightchain
polysaccharidecomposedonlyofβ-D-glucoseunitswhicharejoinedbyglycosidiclinkage
betweenC1ofoneglucoseunitandC4ofthenextglucoseunit.
54.Howdoenzymeshelpasubstratetobeattackedbythereagenteffectively?
Ans.Enzymesarehighlyspecific.Theyreactwithsubstratemoleculeandformintermediate
complex.Theyreducethemagnitudeofactivationenergy.
55.DescribethetermD-andL-configurationusedforaminoacidswithexamples.
Ans.Aminoacidexistsbothin‘D’and‘L’forms.Mostnaturallyoccurringaminoacidshave
L-configuration.L-Aminoacidsarerepresentedbywritingthe—NH2grouponlefthandside
andD-aminoacidsarerepresentedbywritingthe—NH2grouponrighthandside.
56.Howwillyoudistinguish1°and2°hydroxylgroupspresentinglucose?Explainwith
reactions.
Ans.Onoxidationwithnitricacid,glucoseaswellasgluconicacidbothyieldadicarboxylic
acid,saccharicacid.Thisindicatesthepresenceofaprimaryalcoholic(—OH)groupin
glucose.
Acetylationofglucosewithaceticanhydridegivesglucosepentaacetatewhichconfirmsthe
presenceoffive—OHgroups.Sinceitexistsasastablecompound,five—OHgroupsshould
beattachedtodifferentcarbonatoms.
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57.Coagulationofeggwhiteonboilingisanexampleofdenaturationofprotein.
Explainitintermsofstructuralchanges.
Ans.Duringdenaturation2and3structuresaredestroyedbut structureremainsintact.
Thecoagulationofeggwhiteonboilingisacommonexampleofdenaturation.
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CBSEClass–12SubjectChemistry
NCERTExemplarSolutions
Chapter14
Biomolecules
MatchingType
Note:MatchtheitemsofColumnIandColumnIIinthefollowingquestions.Morethan
oneoptioninColumnIImaymatchwiththeitemsgiveninColumnI.
58.MatchthevitaminsgiveninColumnIwiththedeficiencydiseasetheycausegivenin
ColumnII.
ColumnI(Vitamins) ColumnII(Diseases)
(i)VitaminA (a)Perniciousanaemia
(ii)VitaminB1 (b)Increasedbloodclottingtime
(iii)VitaminB12 (c)Xerophthalmia
(iv)VitaminC (d)Rickets
(v)VitaminD (e)Muscularweakness
(vi)VitaminE (f)Nightblindness
(vii)VitaminK
(g)BeriBeri
(h)Bleedinggums
(i)Osteomalacia
Ans.(i)-(c)(ii)-(g)(iii)-(a)(iv)-(h)(v)-(d)(vi)-(e)(vii)-(b)
Explanation:
(i) Xerophthalmia(hardeningofcorneaofeye)nightblindness.
(ii) Beriberi(lossofappetite,retardedgrowth).
(iii) Perniciousanaemia(RBCdeficientinhaemoglobin).
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(iv) Scurvy(bleedinggums).
(v)Rickets(bonedeformitiesinchildren)andosteomalacia(softbonesand
jointpaininadults)
(vi) IncreasedfragilityofRBCsandmuscularweakness.
(vii) Increasedbloodclottingtime.
59.MatchthefollowingenzymesgiveninColumnIwiththereactionstheycatalyse
giveninColumnII.
ColumnI(Enzymes) ColumnII(Reactions)
(i)Invertase (a)DecompositionofureaintoNH3andCO2
(ii)Maltase (b)Conversionofglucoseintoethylalcohol
(iii)Pepsin (c)Hydrolysisofmaltoseintoglucose
(iv)Urease (d)Hydrolysisofcanesugar
(v)Zymase (e)Hydrolysisofproteinsintopeptides
Ans.(i)-(d)(ii)-(c)(iii)-(e)(iv)-(a)(v)-(b)
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CBSEClass–12SubjectChemistry
NCERTExemplarSolutions
Chapter14
Biomolecules
AssertionandReasonType
Note:Inthefollowingquestionsastatementofassertionfollowedbyastatementof
reasonisgiven.Choosethecorrectansweroutofthefollowingchoices.
(i)Assertionandreasonbotharecorrectstatementsandreasonexplainstheassertion.
(ii)Bothassertionandreasonarewrongstatements.
(iii)Assertioniscorrectstatementandreasoniswrongstatement.
(iv)Assertioniswrongstatementandreasoniscorrectstatement.
(v)Assertionandreasonbotharecorrectstatementsbutreasondoesnotexplainassertion.
60.Assertion:D(+)–Glucoseisdextrorotatoryinnature.
Reason:‘D’representsitsdextrorotatorynature.
Ans.(iii)Assertioniscorrectstatementandreasoniswrongstatement.
Explanation:GlucoseiscorrectlynamedasD(+)-glucose.‘D’beforethenameofglucose
representstheconfigurationwhereas‘(+)’representsdextrorotatorynatureofthemolecule.
Theletters‘D’or‘L’beforethenameofanycompoundindicatetherelativeconfigurationof
aparticularstereoisomer.
61.Assertion:VitaminDcanbestoredinourbody.
Reason:VitaminDisfatsolublevitamin.
Ans.(i)Assertionandreasonbotharecorrectstatementsandreasonexplainstheassertion.
Explanation:Fatsolublevitaminsaresolubleinfatandoilsbutinsolubleinwater.Theycan
bestoredinliverandadipose(fatstoring)tissues.
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62.Assertion:β-glycosidiclinkageispresentinmaltose,
Reason:MaltoseiscomposedoftwoglucoseunitsinwhichC–1ofoneglucoseunitislinked
toC–4ofanotherglucoseunit.
Ans.(iv)Assertioniswrongstatementandreasoniscorrectstatement.
Explanation:
Maltoseiscomposedoftwo -D-glucoseunitsinwhichC1ofoneglucose(I)islinkedtoC4
ofanotherglucoseunit(II).
63.Assertion:Allnaturallyoccurringα-aminoacidsexceptglycineareopticallyactive.
Reason:MostnaturallyoccurringaminoacidshaveL-configuration.
Ans.(v)Assertionandreasonbotharecorrectstatementsbutreasondoesnotexplain
assertion.
Explanation:Exceptglycine,allothernaturallyoccurring -aminoacidsareoptically
active,sincethe -carbonatomisasymmetric.Theseexistbothin‘D’and‘L’forms.Most
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naturallyoccurringaminoacidshaveL-configuration.L-Aminoacidsarerepresentedby
writingthe—NH2grouponlefthandside.
64.Assertion:Deoxyribose,C5H10O4isnotacarbohydrate.
Reason:CarbohydratesarehydratesofcarbonsocompoundswhichfollowCx(H2O)y
formulaarecarbohydrates.
Ans.(ii)Bothassertionandreasonarewrongstatements
Explanation:CompletehydrolysisofDNA(orRNA)yieldsapentosesugar,phosphoricacid
andnitrogencontaininghetero-cycliccompounds(calledbases).InDNAmolecules,thesugar
moietyisβ-D-2-deoxyribose.
65.Assertion:Glycinemustbetakenthroughdiet.
Reason:Itisanessentialaminoacid.
Ans.(ii)Bothassertionandreasonarewrongstatements
Explanation:Theaminoacids,whichcanbesynthesisedinthebody,areknownasnon-
essentialaminoacids.Glycineisanexampleofnon-essentialaminoacid.
66.Assertion:Inpresenceofenzyme,substratemoleculecanbeattackedbythereagent
effectively.
Reason:Activesitesofenzymesholdthesubstratemoleculeinasuitableposition.
Ans.(i)Assertionandreasonbotharecorrectstatementsandreasonexplainstheassertion.
Explanation:Inpresenceofenzyme,substratemoleculecanbeattackedbythereagent
effectivelybecauseactivesitesofenzymesholdthesubstratemoleculeinasuitableposition.
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CBSEClass–12SubjectChemistry
NCERTExemplarSolutions
Chapter14
Biomolecules
LongAnswerType
67.WritethereactionsofD-glucosewhichcan’tbeexplainedbyitsopen-chain
structure.Howcancyclicstructureofglucoseexplainthesereactions?
Ans.Followingreactionsandfactscouldnotbeexplainedbyopenchainstructureof
glucose.
Despitehavingthealdehydegroup,glucosedoesnotgive2,4-DNPtest,Schiff’stestand
itdoesnotformthehydrogensulphiteadditionproductwithNaHSO3.
Thepentaacetateofglucosedoesnotreactwithhydroxylamineindicatingtheabsence
offree—CHOgroup.
Itwasproposedthatoneofthe—OHgroupsmayaddtothe—CHOgroupandformacyclic
hemiacetalstructure.Itwasfoundthatglucoseformsasix-memberedringinwhich—OHat
C-5isinvolvedinringformation.
68.OnthebasisofwhichevidencesD-glucosewasassignedthefollowingstructure?
Ans.Glucoseisanaldohexoseandisalsoknownasdextrose.Itisthemonomerofmanyof
thelargercarbohydrates,namelystarch,cellulose.Itisprobablythemostabundantorganic
compoundonearth.Itwasassignedthestructuregivenbelowonthebasisofthefollowing
evidences:
(i)ItsmolecularformulawasfoundtobeC6H12O6.
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(ii)OnprolongedheatingwithHI,itformsn-hexane,suggestingthatallthesixcarbonatoms
arelinkedinastraightchain.Glucosereactswithhydroxylaminetoformanoximeandadds
amoleculeofhydrogencyanidetogivecyanohydrins.Thesereactionsconfirmthepresence
ofacarbonylgroup(>C=O)inglucose.Glucosegetsoxidisedtosixcarboncarboxylicacid
(gluconicacid)onreactionwithamildoxidisingagentlikebrominewater.Thisindicates
thatthecarbonylgroupispresentasanaldehydicgroup.
69.Carbohydratesareessentialforlifeinbothplantsandanimals.Namethe
carbohydratesthatareusedasstoragemoleculesinplantsandanimals,alsonamethe
carbohydratewhichispresentinwoodorinthefibreofcottoncloth.
Ans.Starchisthemainstoragepolysaccharideofplants.Itisthemostimportantdietary
sourceforhumanbeings.Highcontentofstarchisfoundincereals.Celluloseoccurs
exclusivelyinplantsanditisthemostabundantorganicsubstanceinplantkingdom.Cell
wallofbacteriaandplantsismadeupofcellulose.Webuildfurniture,etc.fromcellulosein
theformofwoodandclotheourselveswithcelluloseintheformofcottonfibre.
70.Explainthetermsprimaryandsecondarystructureofproteins.Whatisthe
differencebetweenα-helixandβ-pleatedsheetstructureofproteins?
Ans.Primarystructureofproteins:Proteinsmayhaveoneormorepolypeptidechains.
Eachpolypeptideinaproteinhasaminoacidslinkedwitheachotherinaspecificsequence
anditisthissequenceofaminoacidsthatissaidtobetheprimarystructureofthatprotein.
Anychangeinthisprimarystructurei.e.,thesequenceofaminoacidscreatesadifferent
protein.
SecondaryStructureofProteins:Thesecondarystructureofproteinreferstotheshapein
whichalongpolypeptidechain.Thesecondarycanexist.Theyarefoundtoexistintwo
differenttypesofstructuresviz. -helixandβ-pleatedsheetstructure.Thesestructures
ariseduetotheregularfoldingofthebackboneofthepolypeptidechainduetohydrogen
bondingbetweencarbonylgroupand—NH—groupsofthepeptidebond. -Helixisoneof
themostcommonwaysinwhichapolypeptidechainformsallpossiblehydrogenbondsby
twistingintoarighthandedscrew(helix)withthecarbonyland—Nhgroupofeachamino
acidresiduehydrogenbondedtothe(>C=O)ofanadjacentturnofthehelix.
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Inβ-structureallpeptidechainsarestretchedouttonearlymaximumextensionandthen
laidsidebysidewhichareheldtogetherbyintermolecularhydrogenbonds.
71.WritethestructuresoffragmentsproducedoncompletehydrolysisofDNA.How
aretheylinkedinDNAmolecule?Drawadiagramtoshowpairingofnucleotidebases
indoublehelixofDNA.
Ans.CompletehydrolysisofDNA(orRNA)yieldsapentosesugar,phosphoricacidand
nitrogencontainingheterocycliccompounds(calledbases).InDNAmolecules,thesugar
moietyisβ-D-2-deoxyribose.
Twonucleicacidchainsarewoundabouteachotherandheldtogetherbyhydrogenbonds
betweenpairsofbases.Thetwostrandsarecomplementarytoeachotherbecausethe
hydrogenbondsareformedbetweenspecificpairsofbases.
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