Every ecosystem depends on a flow of energy through organisms, which can be grouped by how they obtain their energy.Producers are photosynthetic organisms, such as plants and algae. They use light energy to synthesise organic compounds from carbon dioxide in the atmosphere, or dissolved in water in aquatic ecosystems. This transfers energy into the chemical energy store of their biomass. Most of the sugars they make are used as respiratory substrates; the rest are used to make other biological molecules such as starch, cellulose, lipids and proteins.Consumers obtain energy by eating other organisms. Primary consumers (herbivores) eat producers. Secondary consumers eat primary consumers, and tertiary consumers eat secondary consumers.Decomposers break down dead organisms, faeces and urine. Many are saprobionts, such as bacteria and fungi. They secrete enzymes onto the dead material and absorb the soluble products of digestion. This releases energy for the decomposers and returns mineral ions, such as ammonium and phosphate ions, to the soil, where producers can absorb them again.Example: In the food chain grass → rabbit → fox, the grass is the producer, the rabbit is the primary consumer and the fox is the secondary consumer. When the fox dies, fungi and bacteria decompose its body.
Energy flows through an ecosystem in one direction, entering as light and leaving as heat. Nutrients, by contrast, are recycled by decomposers.
Energy flows through an ecosystem in one direction, entering as light and leaving as heat. Nutrients, by contrast, are recycled by decomposers.