Question

Which of the following statements is true about the cycling of oxygen in a pond ecosystem? A. Oxygen cannot cycle because it binds irreversibly to other elements. B. Fish create oxygen through the process of cellular respiration. C. Oxygen cycles through the processes of photosynthesis and cellular respiration.

Answer 1

C is true because all living organisms respire and plants carry on photosynthesis even if they are aquatic.

Answer 2

The correct answer is option C - Oxygen cycles through the processes of photosynthesis and cellular respiration.

While water is broken down to form oxygen during photosynthesis by the water plants, in cellular respiration oxygen is combined with hydrogen to form water. 

While photosynthesis requires carbon dioxide and releases oxygen, cellular respiration requires oxygen and releases carbon dioxide. It is the released oxygen that is used by humans and most other organisms for cellular respiration.