Which sentence best describes the role of the Calvin cycle in a plant cell?

• A. It splits water molecules to release oxygen.
• B. It absorbs light energy to excite electrons in chlorophyll.
• C. It uses ATP and NADPH to convert carbon dioxide into glucose.
• D. It generates ATP through oxidative phosphorylation.

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the Calvin cycle. The Calvin cycle is a series of biochemical reactions that occur in the stroma of chloroplasts in plant cells. It is part of photosynthesis and is also known as the light-independent reactions or dark reactions because it does not directly require light to proceed.
2. Step 2: Identify the main purpose of the Calvin cycle. The primary role of the Calvin cycle is to use the energy stored in ATP and NADPH (produced during the light-dependent reactions of photosynthesis) to fix carbon dioxide (CO₂) into organic molecules, ultimately forming glucose.
3. Step 3: Eliminate incorrect options. For example, splitting water molecules to release oxygen occurs during the light-dependent reactions, not the Calvin cycle. Similarly, absorbing light energy to excite electrons in chlorophyll is also part of the light-dependent reactions. Generating ATP through oxidative phosphorylation is a process that occurs in cellular respiration, not photosynthesis.
4. Step 4: Focus on the correct description. The Calvin cycle specifically uses ATP and NADPH to convert carbon dioxide into glucose or other carbohydrates, which are essential for the plant's energy storage and structural needs.
5. Step 5: Conclude that the correct answer is: 'It uses ATP and NADPH to convert carbon dioxide into glucose,' as this best describes the role of the Calvin cycle in a plant cell.