What is the primary energy source used by producers during photosynthesis?

• A. Sunlight
• B. Chemical energy from inorganic molecules
• C. Nuclear energy
• D. Heat energy from the environment

Answer: (A)

Sunlight provides the energy for photosynthesis. Chlorophyll and other pigments capture photons and drive the light-dependent reactions, converting light energy into chemical energy in the form of ATP and NADPH. Those energy carriers then fuel the Calvin cycle, which builds sugars from carbon dioxide. Producers rely on this light-driven process to store energy in chemical bonds. In contrast, chemoautotrophs use chemical energy from inorganic molecules, nuclear energy isn’t directly used by cells as an energy source, and heat from the environment isn’t harnessed to power the photosynthetic reactions.