Every living thing needs food. People enjoy eating food. But that's not the reason we eat. People eat to stay alive. We need food so we can grow. We need food for the energy to do things. Our bodies change our food into energy. We use energy when our hearts beat. We use energy when our lungs breathe. We need energy to stay alive. We use the energy to walk, talk, read, sleep, think, and dream.
Just like us, animals of all kinds need food, too. Food and its energy move from one living thing to another. In the ocean, big fish eat little fish. Little fish eat smaller animals or plants that live in the ocean. Food and energy move in a path we call the food chain. It's usually not a straight path. There can be links between many different things. If we draw a picture of the path that food's energy moves in, it begins to look more like a spider web. So the food chain is often called the food web, too. A food web is a diagram or drawing that shows how living things get energy.
The food of almost every living thing begins with sunlight. Green plants can use sunlight to make their own food. Even plants that live in the ocean do this. Some of the smallest living things in the ocean are algae. They are so simple they are not even called plants. Algae don't have roots or stems. They don't even have true leaves. Many of them can't be seen without a microscope. Just because they're so small we can't see them doesn't mean they aren't important. These tiny, floating living things are very important! They use sunlight to make their own food. As they do this, they make oxygen for us and all animals on Earth to breathe.