Question

The ratio of ATP utilization for \(\mathrm{CO_2}\) fixation between \(\mathrm{C_3}\) and \(\mathrm{C_4}\) plants is

• A. \(5:3\)
• B. \(3:5\)
• C. \(2:3\)
• D. \(3:6\)

Hint:

ATP required per \(\mathrm{CO_2}\) fixed: \[ \boxed{ \begin{aligned} \mathrm{C_3} &: 3\ \text{ATP} \mathrm{C_4} &: 5\ \text{ATP} \end{aligned} } \] Thus, \[ \boxed{\mathrm{C_3:C_4}=3:5.} \]

Answer 1

The Correct Option is B

Step 1: Recall ATP requirement for \(\mathrm{CO_2}\) fixation. For fixation of one molecule of \(\mathrm{CO_2}\), \[ \boxed{ \begin{aligned} \mathrm{C_3} &: 3\ \text{ATP} \mathrm{C_4} &: 5\ \text{ATP} \end{aligned} } \] The additional 2 ATP in \(\mathrm{C_4}\) plants are required for regeneration of PEP.

Step 2: Find the ratio. \[ \boxed{ \mathrm{C_3:C_4}=3:5 } \]

Step 3: Choose the correct option. Hence, the correct option is \[ \boxed{(B).} \]