Michigan Test for Teacher Certification (MTTC) Secondary Integrated Science Practice test

What do dark reactions in photosynthesis primarily use?

1. Sunlight directly

2. Oxygen from the air

3. Data from light reactions

4. Soil nutrients

The correct answer is: Data from light reactions

Dark reactions, also known as the Calvin cycle, primarily utilize the data or products generated from the light reactions of photosynthesis. During the light reactions, which occur in the thylakoid membranes of the chloroplasts, sunlight is absorbed and converted into chemical energy in the form of ATP and NADPH. These energy-rich molecules are then utilized in the dark reactions to convert carbon dioxide into glucose through a series of enzymatic steps. While sunlight and oxygen are crucial for the overall process of photosynthesis, they play distinct roles. Sunlight is directly involved in the light reactions, while oxygen is a byproduct rather than a direct input for the dark reactions. Soil nutrients are important for plant growth as they provide essential elements, but they do not take part in the metabolic processes of the dark reactions themselves. Thus, it is the ATP and NADPH generated from the light reactions that drive the dark reactions, confirming that the correct choice is indeed based on the utilization of data derived from the light reactions.