What do plants produce that supports the higher trophic levels of the community?

Pyramid of Productivity

pyramid of productivity shows that productivity (total net biomass production) is highest at the bottom, or first, trophic level, and decrease dramatically as you move up through the higher trophic levels.  At higher levels, many food chains merge. Also, all food chains end up going into the decomposer food chain eventually. Most organisms eat more than one type of food, and many are represented at different trophic levels in different food chains. So the idea of a food chain is a little over- simplifying food chain - graph of whom eats whom, how each level gets energy. Written specific to particular environments and particular communities

they deliver oxygen to the blood

cell regulation is conducted by special proteins.