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Study Questions

(For additional study questions, with answers, please refer to Web Topic 8.8.)

1. The term "dark reactions" was used for many years to describe the reactions for incorporating CO₂in photosynthesis. Why was this term considered appropriate at the time and why is it considered inappropriate now?

2. Photorespiration is generally considered to be a wasteful process that decreases the yield of C₃plants. What experiment would you propose to minimize the role of photorespiration in plants?

3. What would be the consequence in each of the following if the thioredoxins in chloroplasts were reduced not by ferredoxin but by NADPH as is the case for their cytosol counterparts? Assume NADPH is constant. Explain your answer.

A. Rate of starch synthesis.

B. Hexose monophosphate pool in chloroplasts in the dark.

C. Synthesis of malate in C₄ plants.

D. Synthesis of malate in CAM plants assuming an adequate supply of phosphoenolpyruvate.

E. Activity of Rubisco.

4. There is current concern that the level of CO₂is increasing in the biosphere due to the burning of fossil fuels. If the level of atmospheric CO₂were to double, how would the following be affected? Explain your answer.

A. Rate of oxaloacetate synthesis in C₄ plants.

B. Rate of 3-phosphoglycerate synthesis in C₃ plants.

C. Rate of photorespiration in C₃ plants.

D. Yield of wheat in Kansas.

E. Temperature of San Francisco Bay.

5. It has been known for many years that the cytosolic concentration of Pi in leaves increases when plants are shifted from light to dark. What effect does this change on each of the following?

       A. The concentration of fructose-1,6-bisphosphate.

B. Synthesis of sucrose-6-phosphate from a fixed amount of fructose-6-phosphate.

C. Synthesis of sucrose from fructose-6-phosphate

D. Pool of dihydroxyacetone phosphate in chloroplasts.