A-LevelBiologyPhotosynthesis9700/41 · May/June 2022 · Q214 Marks

In eukaryotes, the cells of plants and photosynthetic protoctists contain chloroplasts.

(a)Describe the relationship between the function of a chloroplast and its structure.[4]
(b)Outline the main features of cyclic photophosphorylation.[3]
(c)Red algae are aquatic protoctists that are multicellular. The cells of red algae have chloroplasts containing photosynthetic pigments. Many red algae live in deep water. Two of the accessory pigments of red algae chloroplasts are: • phycoerythrin (appears red), often present in large concentrations • phycocyanin (appears blue). The first few metres of water nearest the surface absorb the red wavelengths of light. If the water also contains particles of organic material it absorbs blue wavelengths. [Figure 2.1] Describe the differences in the absorption spectra of the three photosynthetic pigments shown in Fig. 2.1 and explain how these differences help red algae to survive in deep water.[7]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2022). The mark or mark type is shown in brackets.

[4] (a) any four from: structure function 1 thylakoid(s) / granum / grana light dependent reaction / photophosphorylation ; 2 thylakoid membrane(s) have (named), pigments / photosystems / LHC / electron carriers /ETC/ ATP synthase ; 3 thylakoid membranes / grana, have large surface area / are many in number to absorb (more) light ; 4 stroma for light independent reaction / Calvin cycle; 5 stroma has, (named) enzymes / RuBP / reduced NADP ; 6 stroma colourless OR stroma contains water so light reaches thylakoids OR as a medium for reactions / for photolysis 7 DNA / ribosomes make (named), chloroplast proteins / proteins for photosynthesis ; 8 starch grains / lipid droplets store, (named) product of photosynthesis / (chemical) energy ; 9 envelope compartmentalisation ;
[3] (b) any three from: 1 light excites electrons in, P700/PS1 (reaction centre chlorophyll); 2 electrons passed, along carriers / to ETC; 3 H+ / protons, pumped into thylakoid, space / lumen ; 4 H+ / protons, diffuse (back to stroma) through ATP synth(et)ase; 5 makes ATP; 6 AVP;
[7] (c) any seven from: description D1 identify wavelengths for chlorophyll (a) absorption; D2 identify wavelengths for phycoerythrin absorption ; D3 identify wavelengths for phycocyanin absorption ; D4 chlorophyll (a), has peaks / absorbs mainly, in blue and red ; D5 phycoerythrin absorbs in blue and green and yellow ; D6 phycocyanin absorbs in (green) yellow and red; explanation E7 red algae / deep water, get(s) green (and yellow) light ; E8 chlorophyll (a) absorbs, no / little, green (and yellow) light ; E9 phycoerythrin / phycocyanin / accessory pigments, absorbs wavelengths not absorbed by chlorophyll (a) ; E10 combined pigments absorb, greater range of / any / all, wavelengths ; E11 increases / more / high(er) rate of, light dependent stage / photosynthesis ; E12 (so) more / lots of, (named) organic compounds / growth ;