Regeneration of each RuBP in ` C_(3)` cycle requires

Options

A. 1 ATP
B. 6 ATP
C. 1 ATP and 1 NADPH+ `H^(+)`
D. 3 ATP and 2 NADPH+ `H^(+)`

Answer

To solve the question regarding the regeneration of each RuBP in the C3 cycle, we can break down the process step by step:

### Step 1: Understanding the C3 Cycle
The C3 cycle, also known as the Calvin cycle, is a crucial part of photosynthesis that occurs in plants. It is named "C3" because the first stable product formed is a three-carbon compound called 3-phosphoglycerate (3-PGA).

**Hint:** Remember that the C3 cycle is also known as the Calvin cycle, and it primarily involves the fixation of carbon dioxide.

### Step 2: Initial Reaction
In the first step of the C3 cycle, ribulose bisphosphate (RuBP), which is a 5-carbon compound, combines with carbon dioxide (CO2) in the presence of the enzyme ribulose bisphosphate carboxylase/oxygenase (RuBisCO). This reaction produces two molecules of 3-PGA.

**Hint:** Focus on the role of RuBisCO and the initial reactants involved in the cycle.

### Step 3: Reduction Phase
During the reduction phase, the 3-PGA molecules are converted into glyceraldehyde-3-phosphate (G3P) using energy. This process requires ATP and NADPH, which are generated during the light-dependent reactions of photosynthesis. Specifically, for every molecule of 3-PGA, 2 molecules of ATP and 2 molecules of NADPH are utilized.

**Hint:** Recall the importance of ATP and NADPH in the reduction phase of the Calvin cycle.

### Step 4: Formation of Glucose
Some of the G3P molecules are used to form glucose and other carbohydrates. However, to continue the cycle and regenerate RuBP, some G3P molecules must be converted back into RuBP.

**Hint:** Understand that G3P is a key intermediate that can be used to form glucose or regenerate RuBP.

### Step 5: Regeneration of RuBP
To regenerate RuBP from G3P, the cycle requires additional energy. Specifically, for every three molecules of G3P that are produced, one molecule of RuBP is regenerated. This regeneration process requires 1 ATP molecule.

**Hint:** Remember that the regeneration of RuBP is crucial for the cycle to continue, and it specifically requires ATP.

### Final Answer
Thus, the regeneration of each RuBP in the C3 cycle requires **1 ATP**.

**Correct Answer:** 1 ATP