Final answer:
Oxygen is produced through photosynthesis and used in cellular respiration as ATP.
Step-by-step explanation:
The substance produced through photosynthesis and used in cellular respiration is oxygen.
During photosynthesis, plants use sunlight, carbon dioxide, and water to produce glucose and oxygen. This glucose is then used in cellular respiration, a process that occurs in both plants and animals, to produce ATP (adenosine triphosphate), which is the main energy source for cells.