The first link in every food chain is a primary producer. The primary producer converts inorganic compounds, such as carbon dioxide and water, into organic compounds that can be used as energy. Producers can be photosynthetic or chemosynthetic, depending on the source of energy they use to make their food.
In photosynthesis, a photosynthetic producer uses the light of the sun to convert carbon dioxide and water into glucose, a sugar that can be used as energy. A chemosynthetic producer uses the energy from compounds, such as those containing sulfur, to make their own food. The ultimate product of both photosynthesis and chemosynthesis is sugar, the energy currency of organisms.
Many of the producers in ecosystems are green plants. Chemosynthetic producers tend to live in environments that are not conducive to life, such as deep sea vents and hot springs.