What is the difference between a food chain and a food web?

A food chain is a simple, linear sequence that shows who eats whom in a biological community. It starts with a primary producer, like a plant, which gets its energy from the sun. Next comes a primary consumer that eats the plant, followed by secondary and tertiary consumers. It represents just one isolated path of energy transfer. If you trace the path from grass to a grasshopper, then to a frog, and finally to a snake, you are looking at a single food chain.

A food web is a collection of all the different, overlapping food chains in a single ecosystem. In the real world, a frog does not only eat grasshoppers, and a snake does not only eat frogs. A food web accounts for these multiple choices. It looks like a messy spider web of arrows connecting many different plants and animals. This complexity makes ecosystems more resilient; if one food source declines, predators can often rely on another.

The most common mistake students make is drawing the arrows in the wrong direction. When drawing a food chain or web, the arrow should always point from the organism being eaten toward the organism that eats it. This is because the arrow represents the flow of energy. The energy moves from the grass into the grasshopper, so the arrow points to the grasshopper. Another common slip is forgetting that decomposers, like fungi and bacteria, are a vital part of every food web, recycling nutrients back into the soil at every level.