What is the difference between a food chain, a food web, and an energy pyramid?

A food chain is the most basic representation of what organisms consume what. For example, grass gets it energy from the sun, the deer eats the grass, the pack of wolves eats the deer. This is an example of a food chain. It starts with a primary producer (organisms that produce their biomass from inorganic compounds; almost always through photosynthesis), then we have a primary consumer that is a herbivore, and finally we have a secondary consumer that is a carnivore.

A food web is a more realistic representation of how the world works, as it includes multiple relationships. The grass may be consumed by deer and other organisms and the deer may also consume other plants such as shrubs or other grasses. Thus, food webs are more complex and show multiple relationships.

Finally, an energy pyramid shows us how energy is transferred from organism to organisms. They are shown in terms of trophic levels, with primary producers as the first trophic level and the base of the pyramid, primary consumers as the second trophic level and second level of the pyramid, and so forth.

The food chain is only a branch of the entire web and it fails to show that most of the animals get eaten and eat more than one species.