Primary nutritional groups are groups of organisms, divided in relation to the nutrition mode according to the sources of energy and carbon, needed for living, growth and reproduction. The sources of energy can be light and organic or inorganic compounds; the sources of carbon can be of organic or inorganic origin.
The terms aerobic respiration, anaerobic respiration and fermentation do not refer to primary nutritional groups, but simply reflect the different use of possible electron acceptors in particular organisms, such as O2 in aerobic respiration, or nitrate (NO3−), sulfate (SO42−) or fumarate in anaerobic respiration, or various metabolic intermediates in fermentation. Because all ATP-generating steps in fermentation involve modifications of metabolic intermediates instead of the use of an electron transport chain fermentation is often referred to as substrate-level phosphorylation.
Phototrophs: Light is absorbed in photo receptors and transformed into chemical energy.
Chemotrophs: Bond energy is released from a chemical compound.
The freed energy is stored as potential energy in ATP, carbohydrates, lipids or proteins. Eventually, the energy is used for life processes as moving, growth and reproduction.
Some bacteria can alternate phototrophy and chemotrophy, depending on availability of light.
Organotrophs: Organic compounds are used as electron donor.
Lithotrophs: Inorganic compounds are used as electron donor.