Photosynthesis complements respiration by producing the reactants required to initiate respiration, which in turn produces the reactants needed to drive photosynthesis. The two processes are balanced chemical reactions that occur in reverse directions. The general equation for photosynthesis is CO2 + H2O + light energy -> glucose + O2 + H2O, while respiration can be expressed using the general equation glucose+ O2 -> CO2 + H2O + released energy.
Photosynthesis and respiration are the two essential metabolic reactions involved in the collection, storage and release of energy that is vital to sustain the life of an organism. Photosynthesis mainly occurs in the chloroplasts of autotrophic organisms, such as green plants and blue-green algae. Respiration occurs in the mitochondria of all living things.
In photosynthesis, solar energy is transformed into chemical energy and stored in the bonds of glucose molecules. Heterotrophic organisms, such as animals, cannot manufacture organic compounds and therefore rely on the products of photosynthesis to drive cellular respiration.
Glucose found in foods, such as carbohydrates, serves as the primary bio-fuel that undergoes an oxidation process to produce adenosine triphosphate, or ATP molecules. The cells require the energy stored in the bonds of these molecules to perform various functions, such as the synthesis of DNA, RNA and proteins. The waste products of respiration, which include carbon dioxide and water, are released into the environment to be re-used in the process of photosynthesis.