Photosynthesis in which algae, higher plants, and photosynthetic bacteria use light energy to fix inorganic carbon in a high-energy organic form:
Respiration in which organic matter is oxidized in the presence of molecular O2 (aerobic respiration) or anaerobic respiration, which uses oxidants other than O2, such as NO3- or SO42-
Degradation of biomass by bacteria and fungi. Biodegradation of dead organic matter consisting predominantly of plant residues prevents accumulation of excess waste residue and converts organic carbon, nitrogen, sulfur, and phosphorus to simple organic forms that can be utilized by plants.
It is a key part of the biogeochemical cycles of these elements and also leaves a humus residue that is required for optimum
physical condition of soil.
Biodegradation of organic matter, such as occurs in treatment of municipal wastewater by reactions represented in a general sense by,
Methane production by methane-forming bacteria, such as Methanobacterium, in anoxic (oxygen-less) sediments, plays a key role in local and global carbon cycles as the final step in the anaerobic decomposition of organic matter. It is the source of about 80% of the methane entering the atmosphere.
Microbial methane production is a fermentation reaction, defined as an oxidation-reduction process in which both the oxidizing agent and reducing agent are organic substances.
Bacterial utilization and degradation of hydrocarbons. The oxidation of higher hydrocarbons under aerobic conditions by Micrococcus, Pseudomonas, Mycobacterium, and Nocardia is an important environmental process by which petroleum wastes are eliminated from water and soil.
The initial step in the microbial oxidation of alkanes is conversion of a terminal –CH3 group to a –CO2 group followed by β–oxidation,
wherein carbon atoms are removed in 2-carbon fragments. The overall process leading to ring cleavage in aromatic hydrocarbons is the following in which cleavage is preceded by addition of –OH to adjacent carbon atoms: