The graph shows the absorption spectrum for two types of chlorophyll.

(i) Sketch on the graph, the action spectrum of photosynthesis.

(ii) Explain the relationship between the absorption spectrum for chlorophyll and action spectrum of photosynthesis for green plants.

Outline photoactivation of photosystem II in the light-dependent reaction of photosynthesis.

(i) line slightly above absorption spectrum with peaks in red and blue and a trough between but not as low as for absorption spectrum
(ii) energy/light absorbed by pigments/chlorophyll is used for photosynthesis;
peaks in action spectrum correspond to peak absorption by chlorophyll;
differences due to absorption by accessory/other pigments (eg carotene);
least absorption in green range/approximately 600nm as most light reflected;

light/photon absorbed by pigment molecules (in photosystem II)/chlorophyll;
energy/electrons passed to chlorophyll molecule at the reaction centre;
causes electron to be raised to higher energy level / electron is excited;
this electron passed along chain of carrier molecules in photosystem II;

A line above and including all the peaks was required for (a)(i). Most candidates were familiar with the terms absorption and action spectra, but could not explain the relationship between the two in 4(a)(ii). In part (b) most knew that an electron became excited, but how or why this came about was not well explained.

A line above and including all the peaks was required for (a)(i). Most candidates were familiar with the terms absorption and action spectra, but could not explain the relationship between the two in 4(a)(ii). In part (b) most knew that an electron became excited, but how or why this came about was not well explained.