Answer:
oxygen
Explanation:
Dark reactions are also called as the Calvin-Benson cycle, the Calvin Cycle, and light-independent reactions. This is because they do not need light for their execution.
The energy in the form of ATP that is produced during the first part of photosynthesis is used in the maintenance of plant's functions like growth, reproduction etc. However, the carbon di oxide should be changed into carbohydrates. This is what happens during dark reactions when NADH and ATP combine with water and carbon di oxide to form the end product of glucose.
Therefore, Oxygen is not a reactant of dark reactions at all.
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