Which substance has not been identified as an electron donor in various organisms that carry out either oxygenic or anoxygenic photosynthesis?

Question

Quizplus · Accepted Answer

Carbon dioxide is not an electron donor in either oxygenic or anoxygenic photosynthesis. It is the source of carbon that is fixed into organic molecules during photosynthesis. Water, ferrous iron, sulfide ions, and hydrogen are all potential electron donors in various types of photosynthesis.

Which Substance Has Not Been Identified as an Electron Donor