Biomass is material produced by the growth ofmicroorganisms,plants oranimals.[1] Beyond this general definition, there are differences in how the term is used and applied depending on industry or subject-matter norms. For example, it may be more narrowly defined as just plant matter,[2] or as a combination of plant and animal matter.[3]
The composition of a specific source of biomass depends on whether it is derived from plants, animals, microorganisms, or some mixture of all biological matter. Biomass may also contain material from non-biological origin, due to contamination fromanthropogenic activities.[4]
The table below summarizes the main types of biomasses and their typical sources.[5]
Sources of biomass
Category
Examples
Woody biomass
Trees, branches, bark, sawdust
Herbaceous & agricultural biomass
Grasses, straw, husks, shells, crops
Aquatic biomass
Algae, aquatic plants, fish, molluscs
Animal-derived biomass
Manure, fats, bones, carcasses
Microbial biomass
Algae, cyanobacteria, bacteria, yeast
Waste-derived biomass
Municipal waste, sewage, waste construction wood
The composition of biomass on a chemical level is determined by whether it is plant or animal matter.
Biomass contains large amounts ofrenewable energy making it a viable source of fuel and a range of refined products; either as-is, or after a series of conversion steps. One such notable example is the production ofbio-ethanol.[6]
There is a general classification of biomass that is produced or sourced for conversion processes.[7] Biofuels such as bioethanol and biodiesel, and bioplastics, are typically derived from primary or “first-generation” source energy-dense plants and oils such asrapeseed,sugarcane, orcorn. Their high content of sugars and oils makes them ideal as feedstocks, however, there are drawbacks to their use. As well as inflating the price of the chosen crop due to increased demand, arable land that would otherwise be used to grow food for human and animal consumption is rendered unavailable.
Secondary or “second-generation” source biomass encompasses a much wider variety of plant and animal matter. It may be derived from a relatively pure source, such as wood chippings or grass, or it may be a less well defined solid waste stream. This type of biomass is far more challenging to work with, as it contains a more varied mixture of compounds that cannot be easily converted into useful products. Despite this, there continues to be intensive research and industry interest in second-generation biomass conversion processes[8] due to its potential to re-use potentially valuable products and derivative products that would otherwise be wasted by incineration.
In ecological studies, biomass refers to the total amount of biological organisms that are present in a given environment or ecosystem. It may encompass the entirety of biological matter, or a subset of species or individuals. It is typically expressed as the total weight of carbon that is contained within the chosen group of organisms. A 2017 estimate of the total amount of biomass within the biosphere is approximately 550 gigatons of carbon, with a significant majority of this being terrestrial plants (approx. 450 Gt C).[9]
^IUPAC Compendium of Chemical Terminology (5th ed.). International Union of Pure and Applied Chemistry. 2025. p. 148.{{cite book}}: CS1 maint: date and year (link)
^Alfano, Simon; Berruti, Federico; Denis, Nicolas; Santagostino, Alberto (November 2016)."The future of second-generation biomass"(PDF).Sustainability and Resource Productivity – via McKinsey.
^Bar-On, Yinon M.; Philips, Rob; Milo, Ron (2017)."The biomass distribution on Earth".Proceedings of the National Academy of Sciences.115 (25): 1.
