Here's how it works:

* Sun: The sun is the ultimate source of energy for most ecosystems.

* Producers: Plants and algae capture the sun's energy through photosynthesis and convert it into chemical energy stored in their tissues.

* Consumers: Animals eat plants or other animals, transferring the stored energy up the food chain.

* Decomposers: Bacteria and fungi break down dead organisms and waste, returning nutrients to the soil for plants to use.

This transfer of energy is not 100% efficient, with some energy being lost as heat at each step. This is why food chains have limited levels – the amount of energy available decreases with each level.