Question

Photosynthesis:

1. 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 result?

2. Compare and contrast the process of photosynthesis in green plants and sulfur bacteria.

Answer 1

Light energy is used in light-dependent reactions to reduce NADP⁺ and to produce ATP. Molecules of chlorophyll are responsible to absorb photons of light energy, but only within narrow energy ranges (specific wavelengths of light). When all the chlorophyll molecules are in use, no additional increase in light intensity will increase the rate of photosynthesis that they can absorb light energy.

Sulfur bacteria are normally nonmotile, and they are capable of anoxygenic photosynthesis. In contrast to plants, sulfur bacteria mainly use sulfide ions as electron donors. In case of green plants, photolysis of water (an electron donor) produces oxygen molecules, hydrogen ions and electrons. Sulfur bacteria are autotrophs and they can utilize the reverse tricarboxylic acid cycle to fix carbon dioxide. They are often found in the deep sea, which has low light availability. On the other hand, green plants utilize normal tricarboxylic acid cycle to fix carbon dioxide. Photosynthesis occurs in presence of sunlight, carbon dioxide and water.