Photosynthesis:

Carbon dioxide + water +  solar energy + minerals -> food +  oxygen

Food made during photosynthesis may later be used for energy by the plant itself, or by an organism that consumes the plant.  In an organism food is used up, with the release of its stored energy, by the process of respiration. Respiration requires oxygen, a&  releases three products: energy (part of  it is used for doing work, and the rest is not used and is given out as heat energy), carbon dioxide, and water -  the starting products of photosynthesis!