| Aerobes | (Environmental Engineering) Organisms which require molecular oxygen as an electron acceptor for energy production. See anaerobes. |
| Amine | (Environmental Engineering) A functional group consisting of "-NH2." |
| Amino acid | (Environmental Engineering) A functional group which consists of a carbon with a carboxylic acid, "-COOH" and an amine, "-NH2." These compounds are the building blocks for proteins. |
| Anabolism | (Environmental Engineering) Biosynthesis, the production of new cellular materials from other organic or inorganic chemicals. |
| Anaerobes | (Environmental Engineering) A group of organisms that do not require molecular oxygen. These organisms, as well as all known life forms, require oxygen. These organisms obtain their oxygen from inorganic ions such as nitrate or sulfate or from protein. |
| Anthropogenic | (Environmental Engineering) Of, made, or caused by human activity or actions. |
| Autotrophic | (Environmental Engineering) Organisms which utilize inorganic carbon for synthesis of protoplasm. Ecologists narrow the definition further by requiring that autotrophs obtain their energy from the sun. In microbiologist parlance, this would be a photoautotroph. See photoautotrophic and chemoautotrophic. |
| Biosynthesis | (Environmental Engineering) Catabolism, the production of new cellular materials from other organic or inorganic chemicals. |
| Carbonyl | (Environmental Engineering) A functional group with an oxygen atom double bonded to a carbon atom. |
| Catabolism | (Environmental Engineering) The production of energy by the degradation of organic compounds. |