Question

How many ATPs are required in \(C_3\) and \(C_4\) plants respectively for net production of 12 G3P molecules (PGAL entering cytosol) during dark reaction?

• A. \(54\) and \(90\)
• B. \(18\) and \(30\)
• C. \(18\) and \(18\)
• D. \(108\) and \(180\)

Hint:

Remember: For one glucose molecule \(C_3\) pathway requires \(18ATP\). \(C_4\) pathway requires \(30ATP\). Since one glucose = two G3P molecules, 12 G3P corresponds to six glucose equivalents.

Answer 1

The Correct Option is D

Concept: For production of one net G3P molecule: \[ 3CO_2 + 9ATP + 6NADPH \] are required in \(C_3\) cycle. For \(C_4\) plants, an additional \(2ATP\) is required per \(CO_2\) fixed. Thus: \[ 3CO_2 \rightarrow 15ATP \] for one net G3P.

Step 1: ATP required in \(C_3\) plants. One net G3P requires \[ 9ATP \] For \(12\) G3P: \[ 12\times 9=108ATP \] \[ \boxed{ATP_{C_3}=108} \]

Step 2: ATP required in \(C_4\) plants. One G3P requires \[ 15ATP \] For \(12\) G3P: \[ 12\times 15=180ATP \] \[ \boxed{ATP_{C_4}=180} \] Therefore, \[ (108,\;180) \] Hence option \((D)\) is correct.