What is the overall purpose of photosynthesis in plants?

• A. To break down glucose for energy.
• B. To generate NADH for respiration.
• C. To release carbon dioxide.
• D. To convert light energy into chemical energy stored in sugars.

Answer: (D)

Plants take light energy and convert it into chemical energy stored in sugars. This energy capture is the main purpose, because the sugars store energy in stable chemical bonds that the plant can use for growth, maintenance, and metabolism. In the light-dependent reactions, chlorophyll absorbs photons to produce ATP and NADPH. Those energy carriers then power the Calvin cycle, which fixes carbon dioxide from the air into three-carbon sugars, ultimately building the carbohydrates the plant needs. Oxygen is released as a byproduct of these processes.

Breaking down glucose for energy describes cellular respiration, a separate process that releases energy from sugars. Generating NADH for respiration refers to respiration, not photosynthesis—photosynthesis makes NADPH, not NADH. Releasing carbon dioxide would contradict what photosynthesis does, since it consumes CO2 to build sugars rather than releasing it.