In such a pond that contains algae and fish, what processes are happening?

Question

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In a pond with algae and fish, both photosynthesis (carried out by the algae) and cellular respiration (carried out by both the algae and the fish) are happening. The algae use photosynthesis to produce energy, and the fish use cellular respiration to convert organic matter into energy. During the day, the algae produce more oxygen through photosynthesis, which the fish use for cellular respiration. At night, the algae consume oxygen through cellular respiration, and the fish produce carbon dioxide through their own cellular respiration. Therefore, both processes are simultaneously occurring in the pond.

In Such a Pond That Contains Algae and Fish, What