Question

As compared to C${}_3$ plants, how many additional molecules of ATP are needed for the net production of one molecule of hexose sugar by C${}_4$ plants?

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

Answer 1

Answer: (C)

Twelve

In C₄ -plants every CO₂ molecule has to be fixed twice, so these plants are needed more energy for the synthesis of hexose sugar molecules than C₃ -plants in which CO₂ has to be fixed only once. 18 ATP molecules are required by C₃-plants for the synthesis of one molecule of hexose sugar while 30 ATP molecules are needed by the C₄ -plants for the same. Thus, C₄ -plants have a need of 12 ATP molecules extra than C₃ -plants for the synthesis of one molecule of hexose sugar.

So, the correct option is 'Twelve'.