This document defines key concepts in ecology and ecosystems, including biotic and abiotic factors and food relationships. It explains that an ecosystem is a community of living and non-living things within an environment, and comprises biotic factors like plants and animals as well as abiotic factors such as water, soil and sunlight. Food chains show the order in which organisms obtain energy from food, with producers, consumers and decomposers playing different roles. Food webs depict the complex interconnections between multiple overlapping food chains within an ecosystem.