Advanced Placement (AP) Biology Practice Exam

What does the Calvin Cycle achieve?

1. Light-dependent reactions that capture sunlight

2. Carbon fixation and synthesis of carbohydrates

3. Release of oxygen as a byproduct

4. Breakdown of glucose for energy

The correct answer is: Carbon fixation and synthesis of carbohydrates

The Calvin Cycle, which takes place in the stroma of chloroplasts, fundamentally achieves carbon fixation and the synthesis of carbohydrates. Through a series of reactions, it captures carbon dioxide from the atmosphere and processes it into glucose and other organic molecules that the plant can use for energy and growth. This cycle is powered by the ATP and NADPH generated during the light-dependent reactions of photosynthesis. The importance of this process lies in its role as the mechanism through which inorganic carbon is converted into organic compounds, making it a critical part of the overall photosynthetic process and essential for the survival of most life forms on Earth, as it forms the basis of the food web. In contrast to the other options, while the light-dependent reactions focus on capturing sunlight and generating energy, the Calvin Cycle is distinctly the series of reactions responsible for carbon fixation. The release of oxygen is a byproduct of the light-dependent reactions, not the Calvin Cycle, and the breakdown of glucose for energy occurs during cellular respiration, which is separate from photosynthesis. Thus, the central achievement of the Calvin Cycle is accurately represented in the correct response.