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Name: Lizzy
Status: student
Grade: 6-8
Location: CA
Country: USA
Date: Spring 2012

I was wondering, why do humans and other life forms require a balance of carbon dioxide in the atmosphere?

Carbon dioxide is absorbed by plants as part of their metabolism. Their end product is oxygen, which all animal life requires. In addition, some life forms require carbon dioxide to balance their pH (acidity), although mammals can survive in a carbon dioxide – free environment for time periods because the body has a mechanism to control pH. In the long term the level of carbon dioxide in the atmosphere is increasing, largely from the combustion of hydrocarbon fuels. The weight of the experimental evidence leads to the conclusion that if these emissions continue uncontrolled, the temperature of the atmosphere (and the Earth’s surface) will increase to levels that will be hazardous to all living species.

Vince Calder

Animals don't need carbon dioxide; they need carbon and oxygen to be separate. They get carbon by eating plants, and oxygen by breathing in. Animals burn carbon to get the energy they need to move around. Burned carbon is carbon dioxide. Animals throw this away by breathing out.

Plants get energy from the sun. They breathe in carbon dioxide, and use the sun's energy to take the oxygen off, so they can use the carbon to make stems, leaves, and fruit. They throw the oxygen away by breathing out.

So carbon goes back and forth between animals and plants. Animals add oxygen to it; plants strip the oxygen off.

Tim Mooney

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