Question

As compared to a C3-plant, how many additional moleules of ATP are needed for net production of one molecule of hexose sugar by C4-plants:

• A. Zero
• B. Six
• C. Two
• D. Twelve

Answer 1

The correct option is D Twelve

In C4 plants, fixation of one carbon dioxide requires 5 ATP and 3 NADPH when compared to 3 ATP and 2 NADPH in C3 plants.
In both plants, Calvin cycle needs to make a total of 6 turns to produce a glucose molecule.
Hence, C4 plants need 12 ATP's more than C3 plants to synthesize an hexose molecule.