Class11Biology

BiologicalClassification

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Exercise2.1

Discuss how classification systems have undergone several changes

over a period of time?

SOLUTION:

Theclassificationsystemshaveundergoneseveral

changeswithtime.Thefirstattemptofclassificationwas

madebyAristotle.Heclassifiedplantsasherbs,shrubs,

andtrees.Animals,ontheotherhand,wereclassifiedon

thebasisofpresenceorabsenceofredbloodcells.This

systemofclassificationfailedtoclassifyalltheknown

organisms.Therefore,Linnaeusgaveatwokingdom

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systemofclassification.ItconsistsofkingdomPlantae

andkingdomAnimalia.However,thissystemdidnot

differentiatebetweenunicellularandmulticellular

organismsandbetweeneukaryotesandprokaryotes.

Therefore,therewerelargenumbersoforganismsthat

couldnotbeclassifiedunderthetwokingdoms.

Tosolvetheseproblems,afivekingdomsystemof

classificationwasproposedbyR.HWhittakerin1969.

Onthebasisofcharacteristics,suchascellstructure,

modeofnutrition,presenceofcellwall,etc.,five

kingdoms,Monera,Protista,Fungi,Plantae,and

Animaliawereformed.

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Exercise2.2

State two economically important uses of:

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(a) Heterotrophic bacteria

(b) Archaebacteria

SOLUTION:

(a)Heterotrophicbacteria

a)Theyactasdecomposersandhelpintheformationof

humus.

b)Theyhelpintheproductionofcurdfrommilk.

c)Manyantibioticsareobtainedfromsomespeciesof

bacteria.

d)Manysoilbacteriahelpinfixationofatmospheric

nitrogen.

(b)Archaebacteria

a)Methanegasisproducedfromthedungofruminants

bythemethanogens.

b)Methanogensarealsoinvolvedintheformationof

biogasandsewagetreatment.

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Exercise2.3

What is the nature of cell-walls in diatoms?

SOLUTION:

Thecellwallsofdiatomsaremadeofsilica.Theircell

wallconstructionisknownasfrustule.Itconsistsoftwo

thinoverlappingshellsthatfitintoeachothersuchasa

soapbox.Whenthediatomsdie,thesilicaintheircell

wallsgetsdepositedintheformofdiatomaceousearth.

Thisdiatomaceousearthisverysoftandquiteinert.Itis

usedinfiltrationofoils,sugars,andforotherindustrial

purposes.

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Exercise2.4

Find out what do the terms algal bloom and red-tides signify

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Exercise2.5

How are viroids different from viruses?

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Exercise2.6

Describe briefly the four major groups of Protozoa.

SOLUTION:

Protozoaaremicroscopicunicellularprotistswith

heterotrophicmodeofnutrition.Theymaybeholozoic,

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saprobic,orparasitic.Thesearedividedintofourmajor

groups.

(1)Amoeboidprotozoaorsarcodines

Theyareunicellular,jelly-likeprotozoafoundinfreshor

seawaterandinmoistsoil.Theirbodylacksaperiplast.

Therefore,theymaybenakedorcoveredbya

calcareousshell.Theyusuallylackflagellaandhave

temporaryprotoplasmicoutgrowthscalledpseudopodia.

Thesepseudopodiaorfalsefeethelpinmovementand

capturingprey.Theyincludefreelivingformssuchas

AmoebaorparasiticformssuchasEntamoeba.

(2)Flagellatedprotozoaorzooflagellates

Theyarefreeliving,non-photosyntheticflagellates

withoutacellwall.Theypossessflagellaforlocomotion

andcapturingprey.Theyincludeparasiticformssuchas

Trypanosoma,whichcausessleepingsicknessinhuman

beings.

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(3)Ciliatedprotozoaorciliates

Theyareaquaticindividualsthatformalargegroupof

protozoa.Theircharacteristicfeaturesarethepresence

ofnumerousciliaontheentirebodysurfaceandthe

presenceoftwotypesofnuclei.Alltheciliabeatinthe

samedirectiontomovethewaterladenfoodinsidea

cavitycalledgullet.Theyincludeorganismssuchas

Paramoecium,Vorticella,etc.

(4)Sporozoans

Theyincludediseasecausingendoparasitesandother

pathogens.Theyareuninucleateandtheirbodyis

coveredbyapellicle.Theydonotpossessciliaor

flagella.Theyincludethemalariacausingparasite

Plasmodium.

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Exercise2.7

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Plants are autotrophic. Can you think of some plants that are

partially heterotrophic?

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Exercise2.8

What do the terms phycobiont and mycobiont signify?

SOLUTION:

Phycobiontreferstothealgalcomponentofthelichens

andmycobiontreferstothefungalcomponent.Algae

containchlorophyllandpreparefoodforfungiwhereas

thefungusprovidessheltertoalgaeandabsorbswater

andnutrientsfromthesoil.Thistypeofrelationshipis

referredtoassymbiotic.

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Exercise2.9

Give a comparative account of the classes of Kingdom Fungi under

the following:

(i) Mode of nutrition

(ii) Mode of reproduction

SOLUTION:

(A)Phycomycetes:Thisgroupoffungiincludes

memberssuchasRhizopus,Albugo,etc.

(i)Modeofnutrition

Theyareobligateparasitesonplantsorarefoundon

decayingmattersuchaswood.

(ii)Modeofreproduction

Asexualreproductiontakesplacethroughmotile

zoosporesornon-motileaplanosporesthatareproduced

endogenouslyinsporangium.

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Sexualreproductionmaybeofisogamous,

anisogamous,oroogamoustype.Itresultsinthe

formationofthick-walledzygospore.

(B)Ascomycetes:Thisgroupoffungiincludesmembers

suchasPenicillium,Aspergillus,Claviceps,and

Neurospora.

(i)Modeofnutrition

Theyaresporophytic,decomposers,parasiticor

coprophilous(growingondung).

(ii)ModeofreproductionbrgtAsexualreproduction

occursthroughasexualsporesproducedexogenously,

suchasconidiaproducedonconidiophores.

Sexualreproductiontakesplacethroughascospores

producedendogenouslyinsaclikeasciandarranged

insideascocarps.

(C)Basidiomycetes:Thisgroupoffungiincludes

memberssuchasUstilago,AgaricusandPuccinia.

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(i)Modeofnutrition

Theygrowasdecomposersinsoiloronlogsandtree

stumps.Theyalsooccurasparasitesinplantscausing

diseasessuchasrustsandsmuts.

(ii)Modeofreproduction

Asexualreproductiontakesplacecommonlythrough

fragmentation.Asexualsporesareabsent.

Sexorgansareabsentbutsexualreproductiontakes

placethroughplasmogamy.Itinvolvesfusionoftwo

differentstrainsofhyphae.Theresultingdikaryongives

risetoabasidium.Fourbasidiosporesareproduced

insideabasidium.

(D)Deuteromycetes:Thisgroupoffungiincludes

memberssuchasAlternaria,Trichoderma,and

Colletotrichum.

(i)Modeofnutrition

Somemembersaresaprophyteswhileothersare

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parasites.However,alargenumberactasdecomposers

ofleaflitter.

(ii)Modeofreproduction

Asexualreproductionistheonlywayofreproductionin

deuteromycetes.Itoccursthroughasexualsporescalled

conidia.

Sexualreproductionisabsentindeuteromycetes

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Exercise2.10

What are the characteristic features of Euglenoids?

SOLUTION:

SomecharacteristicfeaturesofEuglenoidsareas

follows.

Euglenoids(suchasEuglena)areunicellular⇒

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protistscommonlyfoundinfreshwater.

Insteadofcellwall,aprotein-richcellmembrane

knownaspellicleispresent.

Theybeartwoflagellaontheanteriorendofthe

body.

Asmalllightsensitiveeyespotispresent.

Theycontainphotosyntheticpigmentssuchas

chlorophyllandcanthuspreparetheirownfood.

However,inabsenceoflight,theybehavesimilarto

heterotrophsbycapturingothersmallaquaticorganisms.

Theyhavebothplantandanimal-likefeatures,

whichmakesthemdifficulttoclassify

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Exercise2.11

Give a brief account of viruses with respect to their structure and

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nature of genetic material. Also name four common viral diseases.

SOLUTION:

Virusesaresub-microscopicinfectiousagentsthatcan

infectalllivingorganisms.Avirusconsistsofgenetic

materialsurroundedbyaproteincoat.Thegenetic

materialmaybepresentintheformofDNAorRNA.

Mostoftheviruses,infectingplants,havesingle

strandedRNAasgeneticmaterial.Ontheotherhand,

thevirusesinfectinganimalshavesingleordouble

strandedRNAordoublestrandedDNA.

Bacteriophagesorvirusesinfectingbacteriamostlyhave

doublestrandedDNA.Theirproteincoatcalledcapsidis

madeupofcapsomeresubunits.Thesecapsomeresare

arrangedinhelicalorpolyhedralgeometricforms.

A.I.D.S,smallpox,mumps,andinfluenzaaresome

commonexamplesofviraldiseases.

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Exercise2.12

Organise a discussion in your class on the topic- Are viruses living

or non-living?

SOLUTION:

Virusesaremicroscopicorganismsthathave

characteristicsofbothlivingandnon-living.Avirus

consistsofastrandofDNAorRNAcoveredbyaprotein

coat.Thispresenceofnucleicacid(DNAorRNA)

suggeststhatvirusesarealive.Inaddition,theycanalso

respondtotheirenvironment(insidethehostcell)ina

limitedmanner.However,someothercharacters,such

astheirinabilitytoreproducewithoutusingthehostcell

machineryandtheiracellularnature,indicatethat

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virusesarenon-living.Therefore,classifyingviruseshas

remainedamysteryformodernsystematics.

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