A food chain is a linear sequence of organisms through which nutrients and energy pass, starting with a producer organism and ending with a top predator. Each organism in the food chain feeds on the one below it, and is in turn eaten by the one above it. For example, grass grows (producer), grasshoppers eat the grass (primary consumer), birds eat the grasshoppers (secondary consumer), hawks eat the birds (tertiary consumer).
A food web is a more complex diagram that shows how multiple food chains are interconnected. In a food web, each organism can have multiple predators and multiple prey, and the feeding relationships can be more complex than a simple linear sequence. For example, a grasshopper may eat grass, but it may also be eaten by birds, snakes, and other predators. A hawk may eat birds, but it may also eat grasshoppers, mice, and other prey.