The Oxygen Cycle: Lesson for Kids

Instructor: Debra Patuto

Debra has taught at elementary levels and has an M.ed with certification in elementary education and special education

This lesson is about the oxygen cycle and its importance to all living things on Earth. We will learn about the never-ending cycle in which oxygen is made and used, then test your knowledge with a brief quiz.

What Is Oxygen?

You must have oxygen in order to have life. It is a colorless and odorless gas that is in about 20% of Earth's atmosphere (air). You will find oxygen in the ozone layer, carbon dioxide, water and Earth's crust.

And so, the oxygen cycle is very important--it's the process by which new oxygen is being constantly produced from carbon dioxide. After all, humans and all living things release carbon dioxide into the air. So do cars, smoke stacks and fires. And when there's too much carbon dioxide and too little oxygen, living things cannot survive.

How Do We Use Oxygen?

Take a deep breath in and then breathe out. All living things breath through the process called respiration, which is when oxygen is breathed in and carbon dioxide is breathed out. Oxygen is also used is when plants and animals die. As plants and animals decompose, or break down, they use up oxygen and release carbon dioxide.

Chemical reactions also use oxygen. Have you ever left your bike out in the rain and noticed rust starting to develop? When rusting occurs, it oxidizes--or uses up oxygen. (This process uses oxygen but does not make new oxygen.) Fire would not be possible without oxygen. When things burn, they use up oxygen and release carbon dioxide.

How Is Oxygen Made?

As we mentioned, one key ingredient in making oxygen is carbon dioxide. Plants and trees create oxygen through the process of photosynthesis. Photosynthesis is when sunlight hits leaves, and the chlorophyll inside the leaves--along with water from the soil and carbon dioxide from the air--mix together to makes two very important things: food (sugar) for the plant and oxygen for us to breath in. During the process, plants also release extra water that they've absorbed but no longer need.

The carbon dioxide (CO2) is absorbed by the leaf, which releases oxygen (O2) into the air. The plant also releases water (H20) that it does not need.

Phytoplankton is a tiny plant that is found on the top layer of most water environments, such as lakes, ponds and oceans. Phytoplankton makes some of the highest amounts of oxygen through photosynthesis because there is so much of it on the surface of water.

Typically, phytoplankton is microscopic and can not be seen with just your eyes. In this picture, there is so much phytoplankton in the water, you can see it from very far away!
phytoplankton bloom

Where Does the Oxygen Cycle Occur?

The oxygen cycle produces oxygen in four main regions on Earth:

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