Ecosystems consist of living -- biotic -- and non-living -- abiotic -- components. Primary producers -- autotrophs -- create their own food, largely by capturing and using energy from sunlight. Consumers -- heterotrophs -- eat other organisms. These include herbivores that eat plants, carnivores that eat other animals and decomposers that feed on dead animals or plants. Abiotic components include organic materials, such as decaying plant material and dead organisms, inorganic materials, such as water and minerals, and physical factors, such as temperature and sunlight.
Plants and microorganisms use photosynthesis to convert the energy of sunlight to stored energy in the form of molecules, including glucose. Ecosystems obtain 99 percent of their energy through photosynthesis, with the rest coming from bacteria that use chemical means. When heterotrophs eat plants, microorganisms and even other animals, energy is transferred through the ecosystem. Diagrams called food chains show this flow of energy from one organism to another. Ecosystems consist of several food chains that are interlinked to form food webs.
Unlike energy, which enters ecosystems from the outside as sunlight and is eventually lost as heat, chemical elements can cycle endlessly between the biotic and abiotic components of the ecosystem, or between ecosystems. The most abundant of these chemical elements are carbon, oxygen, hydrogen, nitrogen and phosphorus. They enter organisms from the environment, such as the atmosphere, water or soils, and eventually end up in the environment again through processes, such as decomposition.
Ecosystems can also be described by other characteristics. The climate of an ecosystem is the weather conditions over a long period. Productivity refers to the amount of energy captured by the primary producers, such as through photosynthesis. Ecosystems closer to the equator have the potential for greater productivity because they receive more sunlight. Biomass represents the dry weight, without the water content, of the organisms living in an ecosystem. And finally, ecosystems contain species -- groups of organisms with similar characteristics, such as humans and domestic cats.