In photosynthesis, what energy source is required to drive the reaction?

• A. Electrical energy
• B. Light energy
• C. Chemical energy
• D. Thermal energy

Answer: (B)

Light energy from the sun is captured by chlorophyll and used to power the initial steps of photosynthesis. This energy excites electrons and drives the electron transport chain in the chloroplasts, which builds up ATP and NADPH. Those energy-rich molecules later power the Calvin cycle to fix CO2 into sugars. Without light, the light-dependent reactions don’t occur, so the process can’t proceed. The other options don’t fit because electrical and thermal energy aren’t the energy source plants rely on to start photosynthesis, and chemical energy is produced during the process, not the initial energy input.