The Oxygen - Carbon Dioxide Cycle

Most living things on Earth must have oxygen to live. Oxygen is part of the air we breathe. About one-fifth of our air is oxygen. But where does oxygen come from? It might surprise you to learn that some living things make oxygen.

Plants and some other living things make their own food. This process is called photosynthesis. Plants collect energy from the sun. They use it to make their own food, a kind of simple sugar. To do this, plants need carbon dioxide. They take in carbon dioxide from the air. When they make food, they give off oxygen. To them, oxygen is a waste product. To us, oxygen is life!

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