This document provides an overview of ecosystems, including their components, how they function, and key processes like photosynthesis, food chains, and nutrient recycling. It defines ecosystems as relationships between living things and their non-living environments. Producers like plants trap sunlight through photosynthesis to feed consumers, and decomposers break down waste. Nutrients cycle through inputs like sunlight and outputs like oxygen. Ecosystems depend fundamentally on energy from the sun.