In oxygenic photosynthesis in plants and algae, what energy source directly drives the light-dependent reactions?

• A. Heat energy from the environment used to raise electron energy levels
• B. Photons of sunlight absorbed by chlorophyll and other pigments
• C. Energy stored in ATP generated by the Calvin cycle
• D. Chemical energy released by glycolysis in the cytosol

Answer: (B)

Verified step by step guidance

1. Understand that the light-dependent reactions of oxygenic photosynthesis occur in the thylakoid membranes of chloroplasts and require an initial energy input to excite electrons.
2. Recognize that this energy input comes from light energy, specifically photons, which are particles of sunlight absorbed by pigments such as chlorophyll.
3. Recall that when chlorophyll absorbs photons, its electrons become excited to a higher energy state, initiating the electron transport chain that drives the production of ATP and NADPH.
4. Note that heat energy from the environment does not directly raise electron energy levels in photosynthesis, and that ATP and chemical energy from glycolysis are products or inputs in other cellular processes, not the direct energy source for the light-dependent reactions.
5. Conclude that the direct energy source driving the light-dependent reactions is the photons of sunlight absorbed by chlorophyll and other pigments.