Which of the following best describes the primary function of the Calvin cycle in photosynthesis?

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

Answer: (C)

Verified step by step guidance

1. Step 1: Begin by understanding the context of the Calvin cycle, which is part of photosynthesis. Photosynthesis occurs in two main stages: the light-dependent reactions and the light-independent reactions (Calvin cycle). The Calvin cycle is also known as the dark reactions because it does not directly require light.
2. Step 2: Recall that the Calvin cycle takes place in the stroma of the chloroplast and uses ATP and NADPH produced during the light-dependent reactions. These molecules provide the energy and reducing power needed for the cycle.
3. Step 3: Understand the primary function of the Calvin cycle. Its main role is to fix carbon dioxide (CO₂) from the atmosphere into organic molecules. This process is called carbon fixation, and it ultimately leads to the production of glucose, a sugar molecule.
4. Step 4: Clarify that the Calvin cycle does not involve splitting water molecules (this occurs in the light-dependent reactions), absorbing light energy (also part of the light-dependent reactions), or generating ATP through oxidative phosphorylation (a process that occurs in cellular respiration, not photosynthesis).
5. Step 5: Conclude that the correct description of the Calvin cycle's primary function is: 'It converts carbon dioxide into glucose using ATP and NADPH.' This highlights its role in synthesizing organic molecules essential for plant growth and energy storage.