Question

When discussing photosynthesis, some people mistakenly talk about the light reactions and the dark reactions. Why is "dark reactions" an inaccurate name for the Calvin cycle?

- The light reactions occur on the outside of a chloroplast and the Calvin cycle occurs in the center of the chloroplast.
- This implies that the Calvin cycle occurs only at night.
- It does not give proper credit to the scientist who discovered carbon fixation in photosynthesis.
- Dark reactions is another name for photorespiration.
- Both the light reactions and the Calvin cycle are dependent on light.

Answer 1

The term "dark reactions" is misleading for the Calvin cycle because it implies the reactions only occur in the absence of light, which is not the case as they depend on compounds produced by the light-dependent reactions, thus continuing throughout the day. The Calvin cycle operates in the stroma of the chloroplast and is also known as the light-independent reactions or the Calvin-Benson cycle.

Step-by-step explanation:

The term "dark reactions" for the Calvin cycle is misleading because it suggests that this stage of photosynthesis only takes place at night or in the absence of light. However, the Calvin cycle, also known as the light-independent reaction, does not require light directly but relies on energy-rich compounds (ATP and NADPH) produced during the light-dependent reactions. Therefore, the Calvin cycle continues throughout the day as long as the products of the light reactions are available.

The Calvin cycle takes place in the stroma of the chloroplast and is named after Melvin Calvin, the scientist who discovered it. To avoid confusion, scientists and instructors prefer calling this phase the Calvin cycle or the light-independent reactions rather than dark reactions, acknowledging both the continuous nature of the process and the scientific contribution of its discoverers, Melvin Calvin and Andrew Benson, hence it is also referred to as the Calvin-Benson cycle.