Respiration The chemical breakdown of organic food substances such as glucose in the living cells to release energy with or without molecular oxygen. Burning Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Decomposition The process or effect of simplifying a single chemical entity into two or more fragments. Photosynthesis Photosynthesis is the process by which green plants manufacture food (starch/glucose) using carbon dioxide and water in the presence of sunlight and chlorophyll.