Figure 57.1 Energy Flows and Chemical Nutrients Cycle through Ecosystems (A) The flow of energy through ecosystems comes mostly from the sun, which delivers radiant energy for photosynthesis by primary producers. (B) Primary producers then provide energy to organisms at higher trophic levels in food webs, but some of that energy is lost as metabolic heat. (C) Nutrients continually cycle between living organisms and the physical components of ecosystems.