Which best explains the importance of nitrogen in the cycling of energy and matter during photosynthesis?

• A. Nitrogen is released as a gas during the light-dependent reactions.
• B. Nitrogen is the primary source of energy for the Calvin cycle.
• C. Nitrogen directly donates electrons to the electron transport chain in the light reactions.
• D. Nitrogen is a key component of chlorophyll, which is essential for capturing light energy in photosynthesis.

Answer: (D)

Verified step by step guidance

1. Step 1: Begin by understanding the role of nitrogen in biological systems. Nitrogen is a fundamental element found in amino acids, nucleotides, and other biomolecules. In the context of photosynthesis, nitrogen is a key component of chlorophyll, the pigment responsible for capturing light energy.
2. Step 2: Recall the structure of chlorophyll. Chlorophyll molecules contain a porphyrin ring with a central magnesium ion, and nitrogen atoms are part of this ring structure. This nitrogen-containing structure is essential for the molecule's ability to absorb light energy.
3. Step 3: Connect the role of chlorophyll to photosynthesis. Chlorophyll absorbs light energy during the light-dependent reactions of photosynthesis, which drives the production of ATP and NADPH. These energy carriers are then used in the Calvin cycle to synthesize glucose.
4. Step 4: Eliminate the incorrect options. Nitrogen is not released as a gas during the light-dependent reactions, nor is it the primary source of energy for the Calvin cycle. Additionally, nitrogen does not directly donate electrons to the electron transport chain in the light reactions.
5. Step 5: Conclude that the correct explanation is: Nitrogen is a key component of chlorophyll, which is essential for capturing light energy in photosynthesis. This highlights the importance of nitrogen in the cycling of energy and matter during photosynthesis.