When oxygen is not available, organisms have adapted various metabolic processes to generate energy. The specific process used depends on the type of organism.
For instance, anaerobic bacteria can undergo fermentation, a process that allows them to break down glucose without oxygen. This results in byproducts like ethanol or lactic acid, depending on the specific bacteria. For example, yeast typically ferments sugars into alcohol and carbon dioxide in the absence of oxygen, which is a key process in brewing and baking.
In contrast, animal cells, including human cells, rely on a different type of anaerobic metabolism. When oxygen is scarce, they switch to lactic acid fermentation. This allows muscles to continue producing energy, though it results in the accumulation of lactic acid, which can lead to fatigue and discomfort.
Some organisms, like certain archaea, can utilize other molecules as electron acceptors instead of oxygen, participating in processes like methanogenesis. These adaptations illustrate the diverse strategies life forms have evolved to cope with low or no oxygen environments.