As compared to a C3-plant, how many additional molecules of ATP are needed for net production of one molecule of hexose sugar by C4-plants?
- Two
- Six
- Twelve
- Zero
Answer
(3) Twelve
Solution
As per NCERT, the Calvin cycle needs 3 ATP and 2 NADPH for every CO2 fixed.
⇒ For one hexose (6 CO2) in a C3-plant: 6 3 = 18 ATP
In C4-plants, regeneration of PEP from pyruvate in the mesophyll cells uses 2 extra ATP (ATP → AMP) per CO2.
⇒ Extra ATP for one hexose = 6 2 = 12
⇒ Total ATP in C4-plants = 18 + 12 = 30
∴ 12 additional ATP molecules are needed.
Answer: (3)