Edexcel Biology 2011

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1.(a)It is a factor which limits the rate (of photosynthesis / of a reaction) ; Increasing this factor increases the rate (of photosynthesis) ; Until another factor limits the rate / eq ;2

(b)(i)1.Increase in rate from 0 to 300 / 350 (light intensity) ; 2.Reference to manipulated figures to support increase ;
3.Light is the limiting factor / eq ; [accept converse]
4.Rate levels off / eq above 300 / 350 (light intensity) ;
5.Another factor has become limiting ;
6.Named limiting factor: carbon dioxide / temperature /
chloroplasts / chlorophyll ;4

(ii)1.(Provides) carbon dioxide ;
2.Rate of, O2 production / photosynthesis, is greater
(at all light intensities)
above 50 for higher carbonate / CO2 concentration / eq ;
3.Reference to comparative figures for rates / approx. double ; 4.For both concentrations rate starts to levels off at 300 /
350 light intensity / lower concentration levels off above
250 compared with 300 ;
5.Hydrogen carbonate / CO2 concentration is a limiting factor / not
limiting up to light intensity 50 ;3

(iii)Keep temperature constant / place tube containing pond weed in a water bath ;
Reference to rate of reaction / enzymes being affected by temperature changes / temperature affects, solubility / diffusion / volume of oxygen / kinetic energy ;
Repeat / replicate ;
To avoid anomalous / eq results ;
Use the same piece / length of pond weed throughout ;
A different piece could have, more / fewer, leaves / different surface area / eq (and so affect the volume of oxygen produced) ;
Reference to equilibration / eq ;
To make sure pond weed is acclimatised to new conditions ;
No air bubbles in equipment ;
So measuring only gas / oxygen given off ;
Same type of light source ;
So keep wave length the same ;
No external light sources ;
To control the experimental light intensities ;1+1

(c)1.Splitting water in (presence of) light ;
2.H2O  ½ O2 + 2e- + 2H+ ; [allow words]
3.Electrons replace the electrons lost from PS11 / P680 / chlorophyll ; 4.Hydrogen ions picked up by NADP / hydrogen ions reduce NADP ; 5.NADPH / eq used, in light-independent reaction / Calvin cycle / to

reduce carbon dioxide ;3
[14]

2.(a)Affects (rate of) enzyme activity / affects (rate of) enzyme {controlled / catalysed} reaction / correct reference to kinetic energy of molecules / reactants / eq ;
In light-independent stage / Calvin cycle ;2

(b)AStarch (grain) ;
BStroma ;
CGranum / stack of thylakoid ;2
[All correct for two marks, two correct for one mark]

(c)(i)XCO2 / carbon dioxide ;
YPGA / phosphoglyceric acid / phosphoglycerate / GP /
glycerate 3-phosphate / unstable 6-carbon compound ;2

(ii)Light-dependent reaction / grana / thylakoid /
non-cyclic photophosphorylation ;1

(d)1.Sucrose ;
2.Loading by {companion cells / transfer cells / loading cells} ; 3.Active process / requires {energy / ATP} ;
4.In phloem sieve {tubes / elements} ;
5.Reference to {reduction in cell organelles / sieve plates / perforated
end walls} ;
6.Continuous tube ;
7.Mass flow ;
8.Bi-directional flow / flow in any direction ;
9.From {leaves / eq} to {growing regions / storage organs} / reference to
source to sink ;
10.Oxygen by diffusion ;5
[12]

3.(a)X Ribulose bisphosphate / RuBP
5 (carbon atoms)
Y {PGA / GP / eq}
3 (carbon atoms)
[1 mark for each two correct]2
(b)Y is reduced
Using ATP and NADPH+H+;2

(c)1.Reference to sieve tubes (cells) and companion cells; 2.Sieve tube cell has {perforated end walls / sieve plates}; 3.To allow passage of materials / eq;
4.Sieve tube cell has no nucleus / reference to nucleus present in companion cell;
5.No vacuole / few cell organelles / organelles pushed to the sides; 6.To provide more space for translocation;
7.Companion cell has {dense cytoplasm / many mitochondria / eq} for {metabolic activity / energy};
8.Plasmodesmata connecting...
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