Food webs are models that demonstrate how matter and energy is transferred between producers, consumers, and decomposers as the three groups interact within an ecosystem. Transfers of matter into and out of the physical environment occur at every level. In the ecosystem, energy comes from the sun. This sunlight is converted into food by plants via photosynthesis, and the scientific term for this is autotroph. Sun energy from then becomes chemical energy in the form of food. Primary consumers of the food chain eat the plants for energy requirements.