Aerobes use aerobic respiration. Organisms classified as aerobes are eukaryotic and live in an oxygenated environment. Most plants and animals are classified as aerobes. Respiration is the process of breaking down glucose to create energy for the cell. Aerobic respiration requires oxygen to break down the glucose.
Organisms are classified according to how they produce energy through respiration. Organisms that require oxygen are called obligate aerobes. Some organisms can break down glucose without using oxygen through a process called anaerobic respiration. These organisms are called facultative anaerobes. Most anaerobes are prokaryotic organisms like bacteria.
Two other classifications involve the presence of oxygen. Aerotolerant organisms prefer breaking down glucose anaerobically but are able to survive in the presence of oxygen. Microaerophiles use very small amounts of oxygen during respiration.
Individual human cells can create energy with or without the use of oxygen. Anaerobic respiration is carried out by muscle cells when oxygen is not inhaled quickly enough to provide the energy needed during periods of exercise. Anaerobic respiration does not produce as much energy, so it cannot be sustained for long periods of time. Lactic acid is a product of anaerobic respiration. Cells cannot use lactic acid and it must be excreted.