What does the action spectrum reveal about the relationship between light absorption and photosynthesis?

• A. Photosynthesis rate is constant across all wavelengths.
• B. Photosynthesis rate is independent of light absorption.
• C. Photosynthesis rate is highest at wavelengths where absorption is lowest.
• D. Photosynthesis rate is highest at wavelengths where absorption is greatest.

Answer: (D)