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Chapter 8
Blackman found that increasing light intensity above 2000 foot-candles did not lead to any further
increase in the rate of photosynthesis. Can you suggest a hypothesis that would explain this?
(Figure 8.3)
Answer: Light energy is used in light-dependent reactions to reduce NADP+ and to produce
ATP. Molecules of chlorophyll absorb photons of light energy, but only within narrow energy
ranges (specific wavelengths of light). When all chlorophyll molecules are in use, no additional
increase in light intensity will increase the rate that they can absorb light energy.
Under what experimental conditions would you expect the saturation levels for a given number of
chlorophyll molecules to be higher? (Figure 8.8)
Answer: Saturation levels should be higher when light intensity is greater, up to a maximum
level. If it was possible to minimize the size of photosystems by reducing the number of
chlorophyll molecules in each, then the saturation level would also increase.
What would you conclude if “both lights on” did not change the relative rate of photosynthesis?
(Figure 8.12)
Answer: You could conclude that the two photosystems do not function sequentially.