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

During which reactions of photosynthesis is ATP produced?

1. Dark reactions

2. Light reactions

3. Response reactions

4. Oxygen reactions

The correct answer is: Light reactions

In photosynthesis, ATP is produced during the light reactions, which are also sometimes referred to as the photochemical phase. This stage occurs in the thylakoid membranes of the chloroplasts when light energy is captured by chlorophyll and other pigments. During the light reactions, sunlight is absorbed and converted into chemical energy in the form of ATP and NADPH. The process involves the splitting of water molecules, releasing oxygen as a byproduct, and harnessing the energy from electrons that are energized by light. The energy derived from this light-driven electron transport chain is used to phosphorylate ADP to form ATP through a process called chemiosmosis. The other options, such as dark reactions, oxygen reactions, and response reactions, do not specifically relate to the production of ATP. While dark reactions (or the Calvin cycle) utilize ATP produced in the light reactions, they do not themselves produce ATP. Oxygen reactions could refer to the general production of oxygen but do not indicate a process where ATP is generated. Response reactions are not a recognized phase of photosynthesis. Thus, ATP is specifically generated during the light reactions, marking them as a crucial component of the photosynthetic process.