Oxigeno

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The Oxygen - Carbon Dioxide Cycle
By Cindy Grigg Most living things on Earth must have oxygen to live. Oxygen is part of the air we breathe. About one fifth of our air isoxygen. Where does oxygen come from? Plants make oxygen. Plants collect energy from the sun. They use it to make their own food, a kind of simple sugar. Plants need carbon dioxide. It is also part ofthe air. Plants use carbon dioxide to make their food. When they make food, they give off oxygen. To them, oxygen is a waste product. To us, oxygen is life! We breathe in oxygen from the air.Then we breathe out carbon dioxide. We are part of the oxygen-carbon dioxide cycle. A cycle is something that repeats itself. It is the same thing over and over again. The seasons of the year area cycle. Spring, summer, fall, and winter -- a cycle is like a circle with no beginning and no end. The oxygen-carbon dioxide cycle keeps oxygen and carbon dioxide in our air all the time. Weneed oxygen. Plants make oxygen for us. Plants need carbon dioxide. People make carbon dioxide for them. The cycle keeps on going. The Oxygen - Carbon Dioxide Cycle

Questions
1. Where doesoxygen come from? A. The sun makes oxygen. B. People make oxygen. C. Plants make oxygen. 2. The oxygen-carbon dioxide cycle keeps oxygen and carbon dioxide in our air all the time. A. true B.false 3. Plants need ______ from the air. A. carbon dioxide B. water C. sugar 4. People breathe out ______. A. carbon dioxide B. sugar C. oxygen

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5. Plants ______ oxygen.

6.People could not live without oxygen. A. true B. false 7. People and animals breathe in ______. A. oxygen B. sunlight C. water D. carbon dioxide 8. What is a cycle?

Describe the oxygen-carbondioxide cycle.

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Draw five small circles. These circles stand for air. Color one of the circles. Write oxygen by it. Out of every five parts of air, one part is oxygen.