Definition

A producer is a living thing that makes its own food, such as grass using sunlight, water, and air to make sugar, and every food chain starts with a producer, so without them there would be nothing to eat and every animal, humans included, lives on energy a producer first captured from the sun. More formally, a producer (autotroph) makes its own organic food from inorganic materials, usually by photosynthesis using light energy or, in some bacteria, by chemosynthesis using chemical energy, forming the first trophic level of every food chain, though producers convert only about $1$ percent of the sunlight reaching them into stored chemical energy. At the ecosystem level, producers are autotrophs that fix inorganic carbon using either light (photoautotrophs: plants, algae, cyanobacteria) or the oxidation of reduced inorganic compounds such as hydrogen sulfide, ammonia, or hydrogen (chemoautotrophs, found at hydrothermal vents and in soils); gross primary production is the total carbon fixed, net primary production subtracts the producers' own respiration to give the energy available to the rest of the ecosystem, and production is limited by light, water, temperature, and nutrients, especially nitrogen and phosphorus, with global net primary production around $105$ petagrams of carbon per year split roughly evenly between land and ocean.