Which statement best describes the primary role of light energy in photosynthesis?

Which statement best describes the primary role of light energy in photosynthesis?

• A. It is stored as chemical energy in chloroplasts.
• B. It powers chemical reactions that convert carbon dioxide and water into glucose and oxygen.
• C. It is used to break down glucose for energy.
• D. It is used to heat the leaf.

Answer: (B)

Light energy powers the chemical reactions that build sugar from carbon dioxide and water. In the chloroplasts, pigments like chlorophyll capture photons and drive the light-dependent reactions that produce ATP and NADPH. These energy carriers then fuel the Calvin cycle, which uses CO2 to synthesize carbohydrates such as glucose. The oxygen released comes from water split during the light reactions. The energy from light is ultimately stored in the chemical bonds of glucose (and in ATP/NADPH used to make it), not simply used to heat the leaf or to break down glucose for energy.

Light energy powers the chemical reactions that build sugar from carbon dioxide and water. In the chloroplasts, pigments like chlorophyll capture photons and drive the light-dependent reactions that produce ATP and NADPH. These energy carriers then fuel the Calvin cycle, which uses CO2 to synthesize carbohydrates such as glucose. The oxygen released comes from water split during the light reactions. The energy from light is ultimately stored in the chemical bonds of glucose (and in ATP/NADPH used to make it), not simply used to heat the leaf or to break down glucose for energy.