Algae use sunlight to make their own food. An organism that makes its own food is called a producer.
Water fleas eat algae. Small fish eat water fleas. A heron can eat the small fish. These living things form a food chain.
Arrows in a food chain point from the food to the eater. The first arrow points from algae to water fleas. The next points from water fleas to small fish. The last points from small fish to the heron. The arrows show how energy moves along the chain.
Water fleas, small fish and herons are consumers. A consumer gets energy by eating other living things.
Bacteria and fungi break down dead living things. They are called decomposers. As they break down dead things, they release nutrients. Plants and algae can use these nutrients again.
Nutrients are recycled. This means they can be used again. Energy is not recycled. It is passed from food to eater.
Most living things have more than one food source. So, a food chain is part of a larger food web. A food web joins several food chains.