Advanced Placement (AP) Biology Practice Exam

What is a major product of photosynthesis that is typically higher during daylight?

1. Carbon Dioxide

2. Glucose

3. Oxygen

4. ATP

The correct answer is: Oxygen

The major product of photosynthesis that is typically higher during daylight is oxygen. Photosynthesis occurs in two main stages: the light-dependent reactions and the light-independent reactions (Calvin cycle). During the light-dependent reactions, which take place in the thylakoid membranes of chloroplasts when sunlight is available, water molecules are split through photolysis. This process releases oxygen as a byproduct, which is then expelled into the atmosphere. The production of glucose, while also occurring during photosynthesis, is primarily associated with the Calvin cycle, which, although it can occur at night, is mainly driven by the products (ATP and NADPH) generated during the light-dependent reactions that happen during daylight. Therefore, while glucose is a product, its levels may not necessarily be higher during the day in comparison to oxygen. Similarly, ATP is produced during light-dependent reactions, but it is utilized quickly in the Calvin cycle, meaning that its levels fluctuate based on immediate demand rather than consistently accumulating during daylight hours. Carbon dioxide, on the other hand, is a reactant in photosynthesis rather than a product and is typically consumed rather than produced. Thus, oxygen's production as a direct result of the light-dependent reactions explains why it is typically present at