Which enzyme speeds up the reaction between carbon dioxide and ribulose-1,5-bisphosphate (RuBP) to restart the Calvin cycle?

• A. Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase)
• B. NADP+ reductase
• C. ATP synthase
• D. Phosphofructokinase

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the context of the Calvin cycle. The Calvin cycle is a series of biochemical reactions that occur in the stroma of chloroplasts during photosynthesis. It is responsible for fixing carbon dioxide into organic molecules.
2. Step 2: Identify the role of enzymes in the Calvin cycle. Enzymes are biological catalysts that speed up specific reactions. In this case, the enzyme needed facilitates the reaction between carbon dioxide and ribulose-1,5-bisphosphate (RuBP).
3. Step 3: Recall the specific enzyme involved in carbon fixation. The enzyme Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) is responsible for catalyzing the reaction between carbon dioxide and RuBP, forming two molecules of 3-phosphoglycerate (3-PGA).
4. Step 4: Compare the given options. Rubisco is the correct enzyme for this reaction, while NADP+ reductase, ATP synthase, and phosphofructokinase are involved in other processes (e.g., NADP+ reductase in electron transport chain, ATP synthase in ATP production, and phosphofructokinase in glycolysis).
5. Step 5: Conclude that Rubisco is the enzyme that restarts the Calvin cycle by catalyzing the reaction between carbon dioxide and RuBP.