The document discusses key concepts related to food chains and biomass. It defines biomass as the total mass of a living thing excluding water. Biomass is composed of glucose and other substances produced through photosynthesis. A food chain diagrams how organisms feed on each other in an ecosystem, with producers like plants generating their own food, and consumers like herbivores and carnivores eating other organisms or animals. Decomposers feed on dead plants and animals. An example food chain is given of grass being eaten by a grasshopper and further up the chain.