For the synthesis of one molecule of sucrose, how may ATP molecules are required in reduction step of Calvin cycle ?

Options

A. 24 ATP
B. 18 ATP
C. 2 ATP
D. 12 ATP

Answer

To determine how many ATP molecules are required in the reduction step of the Calvin cycle for the synthesis of one molecule of sucrose, we can follow these steps:

### Step 1: Understand the Calvin Cycle
The Calvin cycle consists of three main phases: carbon fixation, reduction, and regeneration. The reduction phase is where 3-phosphoglycerate (3-PGA) is converted into glyceraldehyde-3-phosphate (G3P), which is a precursor for glucose and sucrose.

### Step 2: Identify the Carbon Content of Sucrose
Sucrose is a disaccharide composed of two monosaccharides: glucose and fructose. Each of these monosaccharides contains six carbon atoms, leading to a total of 12 carbon atoms in one molecule of sucrose.

### Step 3: Determine ATP Requirement per Carbon Atom
In the reduction phase of the Calvin cycle, each molecule of 3-PGA (which is a 3-carbon compound) is converted into G3P. This process requires ATP. For every carbon atom that is fixed, 2 ATP molecules are consumed.

### Step 4: Calculate Total ATP for Sucrose
Since sucrose contains 12 carbon atoms, we can calculate the total ATP requirement:
- For 12 carbon atoms:
\[ \text{Total ATP} = 12 \text{ carbon atoms} \times 2 \text{ ATP per carbon} = 24 \text{ ATP} \]

### Conclusion
Thus, for the synthesis of one molecule of sucrose, 24 ATP molecules are required in the reduction step of the Calvin cycle.