Photosynthetic pigmentsEdexcel A-Level Biology B: Flashcards

Exam questions on Photosynthetic pigments

1. A student investigated the effect of wavelength on the rate of photosynthesis. A piece of pondweed in water containing dissolved sodium hydrogencarbonate was placed 15 cm from a lamp. Coloured filters were placed between the lamp and the pondweed in turn, and the number of oxygen bubbles released in five minutes was counted.
   The student found that very few bubbles were released when a green filter was used. Explain this result.2 marks
2. A researcher measured how strongly a purified extract of chlorophyll a absorbed light of different wavelengths, and the rate of photosynthesis of whole leaves at the same wavelengths. The extract absorbed most strongly at about 430 nm and 660 nm. The leaves also photosynthesised at a substantial rate at 480 nm, where chlorophyll a absorbs very little.
   Suggest why the action spectrum of the leaves does not match the absorption spectrum of chlorophyll a alone.2 marks
3. A student extracted pigments from spinach leaves by grinding them in propanone, then separated them by thin-layer chromatography. After the run the solvent front had moved 8.0 cm from the origin. Four pigment spots were visible, at these distances from the origin: carotene 7.6 cm, xanthophyll 5.6 cm, chlorophyll a 4.4 cm and chlorophyll b 3.6 cm.
   Calculate the Rf value of chlorophyll a and of xanthophyll.3 marks