Questions: The dark reaction is also called - Calvin cycle Krebs cycle Dark cycle Citric acid cycle

The answer is the first one: Calvin cycle.

Explanation for each option:

1. Calvin cycle: This is the correct answer. The dark reaction, also known as the light-independent reaction, is part of photosynthesis where carbon dioxide is converted into glucose. This process occurs in the stroma of chloroplasts and does not require light, hence the name "dark reaction." It is also known as the Calvin cycle, named after Melvin Calvin who discovered it.

2. Krebs cycle: This is incorrect. The Krebs cycle, also known as the citric acid cycle, is a part of cellular respiration, not photosynthesis. It occurs in the mitochondria and is involved in the breakdown of glucose to produce energy.

3. Dark cycle: This is incorrect. While the term "dark cycle" might seem related, it is not a standard term used in scientific literature to describe the dark reaction of photosynthesis.

4. Citric acid cycle: This is incorrect. The citric acid cycle is another name for the Krebs cycle, which is part of cellular respiration, not photosynthesis.

In summary, the dark reaction is correctly referred to as the Calvin cycle.