Which of the following are the main reactants required for the light-independent reactions (Calvin cycle) of photosynthesis?

• A. ATP, NADPH, and CO\(_2\)
• B. H\(_2\)O, ATP, and O\(_2\)
• C. NADH, FADH\(_2\), and CO\(_2\)
• D. O\(_2\), glucose, and NADP\(^+\)

Answer: (A)

Verified step by step guidance

1. Step 1: Begin by understanding the context of the problem. The Calvin cycle, also known as the light-independent reactions, is a part of photosynthesis that occurs in the stroma of chloroplasts. It does not require light directly but relies on products generated during the light-dependent reactions.
2. Step 2: Recall the main purpose of the Calvin cycle. It is responsible for fixing carbon dioxide (CO\(_2\)) into organic molecules, such as glucose, using energy and reducing power provided by ATP and NADPH.
3. Step 3: Analyze the options provided. ATP and NADPH are produced during the light-dependent reactions of photosynthesis, and CO\(_2\) is the carbon source for the Calvin cycle. These are the correct reactants required for the Calvin cycle.
4. Step 4: Eliminate incorrect options. H\(_2\)O and O\(_2\) are involved in the light-dependent reactions, not the Calvin cycle. NADH and FADH\(_2\) are electron carriers used in cellular respiration, not photosynthesis. Glucose and NADP\(^+\) are products or intermediates, not reactants of the Calvin cycle.
5. Step 5: Conclude that the correct answer is ATP, NADPH, and CO\(_2\), as these are the main reactants required for the Calvin cycle to synthesize organic molecules.