A food web is similar to a food chain but larger. The diagram combines many food chains into energy relationships among organisms. Food webs show how plants and animals are connected in many ways. The arrow points from the organism being eaten to the organism that eats it.

A food web (or food cycle) is a natural interconnection of food chains. The two extreme categories (trophic levels) are:

1. the autotrophs, and
2. the heterotrophs.

A gradient exists: there are different kinds of feeding relations: herbivory, carnivory, scavenging and parasitism.

Some of the organic matter eaten by heterotrophs, such as sugars, provides energy. Autotrophs and heterotrophs come in all sizes, from microscopic to many tonnes – from cyanobacteria to giant redwoods, and from viruses to blue whales.