Advanced Placement (AP) Biology Practice Exam

Which of the following is NOT a product of light-dependent reactions?

1. Oxygen

2. NADPH

3. Organic Molecules

4. ATP

The correct answer is: Organic Molecules

The light-dependent reactions of photosynthesis occur in the thylakoid membranes of chloroplasts and are responsible for converting light energy into chemical energy. During these reactions, sunlight is absorbed by chlorophyll and other pigments, leading to the photolysis of water, which produces oxygen as a byproduct. In addition to oxygen, the light-dependent reactions produce two important energy-carrying molecules: ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate). ATP serves as an energy currency for various biochemical processes, while NADPH is used as a reducing agent in subsequent reactions. In contrast, organic molecules, such as glucose and other carbohydrates, are produced in the light-independent reactions (Calvin cycle) that utilize the ATP and NADPH generated from the light-dependent reactions. Since organic molecules are synthesized during the Calvin cycle rather than being direct products of the light-dependent reactions, identifying them in this context highlights the distinction between the processes in photosynthesis.