The Photosynthesis Cycle"
The Earth's atmosphere is mostly composed of nitrogen. Oxygen makes up just 21 percent of the air we breathe. Carbon dioxide, argon, ozone, water vapor and other gasses make up a tiny portion of it, as little as 1 percent. These gasses probably came from several processes as the Earth evolved and grew as a planet. But some scientists believe that the Earth's atmosphere would never have contained the oxygen we need without plants. Plants (and some bacteria) release oxygen during photosynthesis, the process they use to change water and carbon dioxide into sugar they can use for food. Photosynthesis is a complex reaction. 6CO2 + 12H2O + Light -> C6H12O6 + 6O2+ 6H2O In other words, while we inhale oxygen and exhale carbon dioxide, plants inhale carbon dioxide and exhale oxygen. Without the sun to feed plants (and the plants to release oxygen), we might not have breathable air. Obviously, plants are important, but not just because they give us food to eat and oxygen to breathe.
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