Biology Unit 4 – Model Answers The ecologists could could have used the mark-release-recaptur mark-release-recapture e method to estimate the the number of one species of this organism in the lake !escribe how how "# Marks$ % &ap &aptur ture e sample sample'' mark mark and rele releas ase( e( ) Appr Appropria opriate te method method of marking marking suggested suggested * method method of marking marking does does not harm harm +sh( # Tak ake e second second sample and and count marked marked organ organisms( isms( 4 ,o ,opulat pulation ion .um in sample% sample% / .um in sample sample) ) * .umber marke marked d in sample)( sample)( The population of this species species evolved adaptations adaptations to the environment Use Use your knowledge of selection to e0plain how "# Marks$ % 1ariat ariation ion in original original colon colonisers isers * mutati mutations ons took took place( place( ) 2ome bette betterr "adapted "adapted for$ surviv survival al "in "in mountain mountains$( s$( # 3r 3reat eater er repro reproduc ductiv tive e succes success( s( 4 All Allele ele fr freu euenc encies ies cha change nge(( AT, is useful in many biological processes 50plain why "4 Marks$ 6eleases 6eleas es energy in small * manageable amounts( "Broken "Brok en down$ in a one step * single bond brok broken( en( 7mmediate energy compound*makes energy available rapidly( ,hosphorylates*adds phosphate( Makes "phosphorylated substances$ more reactive * lowers activation energy( 6eformed*made again( • • • • • •
!escribe how AT, is made in mitochondria "8 Marks$ % 2ubstr 2ubstrate ate level level phosphory phosphorylatio lation n * AT, AT, produced produced in 9rebs 9rebs cycle( cycle( ) 9rebs cycle*link reaction produces reduced coen:yme*reduced .A!*reduced ;A!( # 5lect 5lectron rons s released released from from reduced reduced *coen:ymes *coen:ymes** .A!*;A!( .A!*;A!( 4 "5lectrons$ pass along along carriers*through carriers*through electron transport chain*through series of of redo0 reactions( < 5n 5ner ergy gy re rele leas ased ed(( 8 A! A!,* ,*A! A!, , = ,i( > ,r ,rotons otons move into inter intermemb membrane rane spac space( e( ? AT, sy synt ntha hase se(( 50plain why it is important for plants to produce AT, AT, during respiration in addition to during photosynthesis "< Marks$ 7n the dark no AT, production in photosynthesis( 2ome tissues unable to photosynthesise*produce AT,( AT,( AT, cannot be moved from cell to cell*stored( ,lant uses more AT, than produced in photosynthesis( AT, for active transport( AT, for synthesis "of named substance$( • • • • • •
@umans synthesise more than their body mass of AT, each day 50plain why it is necessary for them to synthesise such a large amount of AT, ") Marks$ AT, is unstable( AT, cannot be stored * is an immediate source of energy( .amed process uses AT,( AT, only releases a small amount of energy at a time( • • • •
50plain the conseuences of leaching of fertiliser into ponds and lakes "# Marks$ % 7nc 7ncre reas ase e algae algae*al *algal gal blo bloom( om( ) i igh ghtt blo block cked ed ou out( t( # ,lant ,lants s cant cant photosyn photosynthesi thesise se * plants plants and*o and*orr algae die( 4 Bacte Bacteria*s ria*sapro aprobiont bionts*5C s*5C feed feed oD*breakdo oD*breakdown wn dead organism organisms( s( < Bacte Bacteria*s ria*sapro aprobiont bionts*5C s*5C use use up o0ygen*ba o0ygen*bacteri cteria a respire respire
!escribe the role of bacteria in making the nitrogen in dead leaves available to growing plants "< Marks$ 2aprobionts*saprophytes( !igest*break down proteins*!.A*nitrogen-containing substances( 50tracellular digestion*release of en:ymes( Ammonia*ammonium produced( Ammonia converted to nitrite to nitrate*ammonia to nitrate( .itrifying "bacteria$* nitri+cation( E0idation( • • • • • • •
&learing the forests and burning the vegetation aDects the carbon dio0ide concentration in the atmosphere !escribe how and e0plain why "4 Marks$ &arbon dio0ide concentration increases( Clearing .o*ess vegetation so no*less photosynthesis * photosynthetic organisms( .o*ess carbon dio0ide removed "from the atmosphere$( Burning Burning*combustion releases * produces carbon dio0ide( •
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!uring photosynthesis' trees convert carbon dio0ide into organic substances !escribe how "8 Marks$ % &arbon dio0ide combines with ribulose bisphosphate*6uB,( ) ,roduces two molecules of glycerate-#-phosphate*3,( # 6educed to triose phosphate*T,( 4 Using reduced .A!,( < Using energy from AT,( 8 Triose phosphate converted to other organic substances* named organic substances*ribulose bisphosphate( > 7n light independent reaction*&alvin cycle( 7n the light-dependent reaction of photosynthesis' light energy generates AT, !escribe how "< Marks$ % ight "energy$ e0cites*raises energy level of electrons in chlorophyll( ) 5lectrons pass down electron transfer chain( # "5lectrons$ reduce carriers*passage involves redo0 reactions( 4 5lectron transfer chain * role of chain associated with chloroplast membranes * in thylakoids * grana( < 5nergy released * carriers at decreasing energy levels( 8 AT, generated from A!, and phosphate*,i *phosphorylation of AT,( !escribe how and e0plain why the eFciency of energy transfer is diDerent at diDerent stages in the transfer "8 Marks$ 2ome light energy fails to strike*is reGected*not of appropriate wavelength( 5Fciency of photosynthesis in plants is low*appro0imately )H eFcient( 6espiratory loss * e0cretion * faeces * not eaten( oss as heat( 5Fciency of transfer to consumers greater than transfer to producers*appro0imately %IH( 5Fciency lower in older animals*herbivores* primary consumers*warm blooded animals*homoiotherms( &arnivores use more of their food than herbivores( • • • • •
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50plain how the intensive rearing of domestic livestock increases net productivity "4 Marks$ 2laughtered when still growing*before maturity*while young so more energy transferred to biomass*tissue*production( ;ed on concentrate *controlled diet *controlled conditions*so higher proportion of "digested$ food absorbed*lower proportion lost in faeces * valid reason for addition( Movement restricted so less respiratory loss * less energy used( 9ept inside*heating*shelter * con+ned so less heat loss * no predators( 3enetically selected for high productivity( •
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2uccession occurs in natural ecosystems !escribe and e0plain how succession occurs "< Marks$ % "&olonisation by$ pioneer "species$( ) &hange in environment * e0ample of change caused by organisms present( # 5nables other species to colonise*survive( 4 &hange in diversity*biodiversity( < 2tability increases * less hostile environment( 8 &lima0 community( !escribe the advantages and disadvantages of using biological agents to control pests "< Marks$ Advantages 2peci+c "to one pest$( Enly needs one application* reproduces( 9eeps*maintains low population( ,ests do not develop resistance( !oes not leave chemical in environment*on crop * no bioaccumulation( &an be used in organic farming( Disadvantages !oes not get rid of pest completely( May become a pest itself( 2low acting* lag phase* takes time to reduce pest population( • • • • • •
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!escribe how a natural occurring separation of two species can lead to 2peciation "< Marks$ 3eographical isolation( 2eparate gene pools * no interbreeding "between populations$( 1ariation due to mutation( !iDerent environmental*abiotic*biotic conditions * selection pressures( 2election for diDerent*advantageous' features*characteristics*mutation* *allele( !iDerential reproductive success * "selected$ organisms survive and reproduce( eads to change in allele freuency( Eccurs over a long period of time( • • • • • • • •
50plain how farming practises increase the productivity of agricultural crops "< Marks$ ;ertilisers*minerals*named ion "added to soil$( 6ole of named nutrient or element eg nitrate*nitrogen for proteins * phosphate*phosphorus for AT,*!.A( ,esticides*biological control prevents damage*consumption of crop( ,esticides*weed killers *herbicides*weeding remove competition( 2elective breeding * genetic modi+cation "of crops$( 3lass*greenhouses enhance temp*&E)* light( ,loughing aerates soil*improves drainage( ,loughing*aeration allows nitri+cation*decreases denitri+cation( Bene+t of crop rotation in terms of soil nutrients*fertility*pest reduction( 7rrigation*watering to remove limiting factor( ,rotection of crops from birds*pests*frost by covers*netting etc( • •
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!escribe how the action of microorganisms in the soil produces a source of nitrates for crop plants "< Marks$ % ,rotein*amino acids*!.A into ammonium compounds * ammonia( ) By saprobionts( # Ammonium*ammonia into nitrite( 4 .itrite into nitrate( < By nitrifying bacteria*microorganisms( 8 .itrogen to ammonia*ammonium( > By nitrogen-+0ing bacteria*microorganisms in soil( 50plain how the use of pesticides can result in resistant strains of insect pests "< Marks$ % 1ariation*variety in pest population(
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!ue to mutation( Allele for resistance( 6eference to selection( ,ests with resistance "survive and$ breed * diDerential reproductive success( 6. 7ncrease in freuency of allele(
