The sun is the ultimate source of energy for life on Earth. Without it, nothing would be able to survive. As a result, living things have evolved special ways to harness the energy of the sun and use it for their own well-being. They have also developed special relationships and interactions that allow energy to be transferred. Once the energy has been captured, it gets passed around through the various organisms in a particular area. This transfer of energy is called a food web. 

In their simplest form, food webs are made of food chains. Food chains show a direct transfer of energy between organisms. A chain might involve a mouse eating some seeds on the forest floor. Then, a snake comes along and eats the mouse. A while later, an owl eats the snake. With each step, some of the energy from the sun, which is trapped within the seeds, is getting passed on. 

Food chains do not accurately portray the transfer of energy in an ecosystem. This is because there are often multiple organisms that can be eaten, and many that can do the eating. For example, the aforementioned mouse might eat seeds, but it also might eat some berries, or maybe even some grass. The mouse might be eaten by a snake, or the owl, or even a fox. The snake could be eaten be the owl, but also might get eaten by a fox or a coyote in the forest. Since each organism can eat multiple things and be eaten by multiple things, a food web is a much more realistic schematic of the transfer of energy within an ecosystem.
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