Find the number of ATP required in the reduction step of the C3 cycle if the cycle is involved in the formation of one sucrose molecule.

Options

A. 12 ATP
B. 24 ATP
C. 18 ATP
D. 6 ATP

Answer

To find the number of ATP required in the reduction step of the C3 cycle (Calvin cycle) for the formation of one sucrose molecule, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Composition of Sucrose**:
- Sucrose is a disaccharide composed of 12 carbon atoms (C12H22O11).

2. **Identify the C3 Cycle**:
- The C3 cycle, also known as the Calvin cycle, involves the fixation of carbon dioxide and the reduction of 3-carbon molecules (3-phosphoglycerate).

3. **ATP Requirement for 3-Carbon Reduction**:
- During the reduction phase of the Calvin cycle, 6 ATP molecules are required to reduce 3 carbon atoms (from 3-phosphoglycerate to glyceraldehyde-3-phosphate).

4. **Calculate ATP for 12 Carbon Atoms**:
- Since 6 ATP are needed for the reduction of 3 carbon atoms, we can set up a proportion to find out how many ATP are needed for 12 carbon atoms:
\[ \text{ATP required for 12 carbon} = \left(\frac{6 \text{ ATP}}{3 \text{ carbon}}\right) \times 12 \text{ carbon} \]
- Simplifying this gives:
\[ \text{ATP required for 12 carbon} = 6 \times 4 = 24 \text{ ATP} \]

5. **Conclusion**:
- Therefore, the total number of ATP required in the reduction step of the C3 cycle for the formation of one sucrose molecule is **24 ATP**.

### Final Answer:
- The number of ATP required is **24** (Option B).