Biology 9700 · AS & A Level · Photosynthesis as an energy transfer process
Photosynthesis as an energy transfer process — practice question
The light-dependent stage of photosynthesis takes place in chloroplasts. During this stage, electrons are released from chlorophyll $a$ molecules and passed on to electron acceptors. If a redox indicator such as DCPIP is added to a suspension of illuminated chloroplasts, electrons are transferred to DCPIP, causing its colour to change from blue to colourless. A student investigated how the wavelength of light (colour of light) affected the rate of photosynthesis.
(a(i))[1]
Explain why the chloroplast suspensions were stored in the dark until they were needed.
(a(ii))[3]
Describe the pattern shown in Fig. 7.1.
(a(iii))[3]
With reference to the light-dependent stage of photosynthesis, Explain why the results in Fig. 7.1 are different for red light and for green light.
(b)[3]
Changes in atmospheric carbon dioxide concentration, light intensity and temperature can alter the rate of photosynthesis. These three factors directly influence different processes in photosynthesis.
Complete Table 7.1 using a tick (✓) to show the processes that are directly affected by each factor or a cross (\times) to show those that are not directly affected.
Indirect effects, where a change in the rate of one process alters a different process, should not be included.
A tick or cross must appear in the final column of every row.
Worked solution & mark scheme
This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: “If light is not absorbed, the light-dependent stage stops.” …