Biology 9700 · AS & A Level · Photosynthesis as an energy transfer process
Photosynthesis as an energy transfer process — practice question
Chloroplasts are one class of organelle within the plastid group. Although the different plastid types differ in structure and function, one plastid type can convert into another when environmental or developmental signals act. Example 1: plants kept in the dark contain plastids called etioplasts, and these do not have chlorophyll. When such plants receive light, the etioplasts rapidly become chloroplasts. Example 2: in the outer tissues of tomato fruits, chloroplasts turn into plastids called chromoplasts as the fruits ripen. The thylakoid membranes break down and chlorophyll synthesis stops. Chromoplasts make and store the red lycopene and orange β-carotene pigments.
(a)[2]
For each of these examples, explain the effect on the rate of photosynthesis when one type of plastid changes into another type of plastid. Example 1. Example 2.
(b)[4]
Outline the method you would use to separate and identify the pigments in an extract of tomato chromoplasts.
(c)[3]
Cyanobacteria are prokaryotic organisms. Plastids are believed to have evolved from cyanobacteria that were taken into larger cells. Experiments show that free-living cyanobacteria can respond to environmental signals in the same way as plastids.
Fig. 2.1 displays the absorption spectra of cyanobacteria grown under two different lighting conditions. One group was cultured under fluorescent light and the other under red light. The range of light wavelengths absorbed by each group of cyanobacteria was then measured under the same lighting conditions.
Using Fig. 2.1 and the information on pages 4 and 5, explain how the different lighting conditions affect the absorption spectra of the two groups of cyanobacteria.
Worked solution & mark scheme
This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “The rate rises as the amount of chlorophyll / number of chloroplasts rises for the light-dependent reaction” …