A-LevelBiologyPhotosynthesis9700/42 · Feb/Mar 2021 · Q49 Marks

Red algae are multicellular photosynthetic protoctists that contain phycoerythrin. Phycoerythrin is a photosynthetic pigment.

(a)(i)With reference to Fig. 4.1, state the wavelength of peak absorption by phycoerythrin.[1]
(a)(ii)Explain how the data in Fig. 4.1 show that phycoerythrin is not the only photosynthetic pigment in red algae.[2]
(a)(iii)Phycoerythrin is not the primary pigment (reaction centre pigment) for photosynthesis in red algae. Suggest the role of phycoerythrin in photosynthesis in red algae.[2]
(b)(i)State the name of a technique that can be used to separate and identify photosynthetic pigments.[1]
(b)(ii)Explain how the results of this technique would be used to confirm that phycoerythrin is present in red algae and not present in a plant with green leaves.[3]

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Mark scheme

Marking points from the official mark scheme (Feb/Mar 2021). The mark or mark type is shown in brackets.

[1] 565 nm;
[1] phycoerythrin does not absorb light above 590–600 (nm) ; A suitable value for absorption that answer the question
[1] (but) photosynthesis still takes place (above 590–600 nm); A suitable value for absorption that answer the question
[1] accessory pigment;
[1] absorbs light energy (up to 595 nm) ; R trap / capture
[1] (and) passes it to, primary pigment / reaction centre / chlorophyll a ;
[1] chromatography;
[1] calculate R value(s);
[1] compare Rf values of pigments (in red algae and green plant);
[1] find pigment present (on chromatogram) from red algae but absent from green plant or Rf value of phycoerythrin will not be the same as Rf values of pigments in green leaves ;
[1] identify pigment using reference values (to confirm it is phycoerythrin) ;

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