because the sun gives off energy which the producers (such as lettuce, leaves and grass) take in to grow for the consumers (such as slugs or snails).
The energy from the sun!
It is the sun.
The primary souce is the SUN
The sun.
In most food webs the Sun is the ultimate source of energy. Some food webs start with chemotrophs and in those cases the source of the energy are chemicals often from underwater volcanoes.
I assume you mean the energy flow diagram. The sun should be present. EDIT: Sorry, food web, I remember now. Its strictly a transfer of material. The sun does not transfer any material to plants, and so is not present in food webs.
The sun
the sun i think
Estuary food webs begin with the conversion of the sun's energy to food energy by plants and plankton.
it is passed by first, the energy from the sun and passed into plants which provide nutrients.
Food chains and food webs are different. This is because the webs have more relative food choices whereas the chains are limited.
The sun and energy made by autotrophs (usually plants but also cyanobacteria and algae)