The material of plants and animals, including their wastes and residues, is called biomass. It is organic, carbon-based material that reacts with oxygen in combustion and natural metabolic processes to release heat. Such heat, especially if at temperatures >400°C, may be used to generate work and electricity. The initial material may be transformed by chemical and biological processes to produce biofuels, i.e. biomass processed into a more convenient form, particularly liquid fuels for transport. Examples of biofuels include methane gas, liquid ethanol, methyl esters, oils and solid charcoal. The term bioenergy is sometimes used to cover biomass and biofuels together.