Photogeochemical reactions may be classified based on thermodynamics and/or the nature of the materials involved. In addition, when ambiguity exists regarding an analogous reaction involving light and living organisms (phototrophy), the term "photochemical" may be used to distinguish a particular abiotic reaction from the corresponding photobiological reaction. For example, "photooxidation of iron(II)" can refer to either a biological process driven by light (phototrophic or photobiological iron oxidation) or a strictly chemical, abiotic process (photochemical iron oxidation). Similarly, an abiotic process that converts water to O under the action of light may be designated "photochemical oxidation of water" rather than simply  "photooxidation of water", in order to distinguish it from photobiological oxidation of water potentially occurring in the same environment (by algae, for example).