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The Oxygen-Carbon Dioxide Gycle
By Cindy Grigg
1l:12 AM
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1
One element that is very important to nearly all living things is
oxygen. Humans and other animals need oxygen to stay alive.
Every time you take a breath, you are filling your lungs with
oxygen.
2
If much of the oxygen in the air disappeared, animals would
not be able to survive. But animals are breathing in oxygen every
day. Why doesn't the air ever run out of oxygen?
3
Plants help provide the oxygen that animals need to survive.
When you breathe out, you release carbon dioxide into the air.
Carbon dioxide is made up of two elements, carbon and oxygen. To make their own food,
plants use carbon dioxide from the air. Then they release oxygen as a waste product.
Humans and other animals breathe in oxygen and release carbon dioxide. This cycle is
known as the oxygen-carbon dioxide cycle.
a
Aboyl.€tghty percent of the oxygen used by animals is replaced by algae. Algae are
classifi-ed as neither plants nor animals, but as protists. They have chlorophyll and can make
their own food by photosynthesis. Algae live world-wide, in oceans, freshwater, and even
on land. Plants living on land replace the remaining twenty percent of the oxygen used by
animals. Because of the oxygen-carbon dioxide cycle, the amount of oxygen in the air stays
fairly constant. As long as there are enough plants on Earth to release oxygen, we will never
run out.
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The Oxygen-Garbon Dioxide Gycle
1' What two elements
is carbon dioxide
2. How do plants use carbon dioxide?
{X}
made of?
{X: Carbohydrate and dioxin
{H} Carbon and dioxin
Carbon and oxygen
Carbohy drate and oxide
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3.
Which of the following correctly
describes the oxygen-carbon dioxide
cycle?
{X: Humans and other animals breathe
in oxygen and release carbon dioxide.
Plants absorb carbon dioxide and
release oxygen.
The oxygen-carbon dioxide cycle
keeps the amount of oxygen in the air
fairly constant.
411 of the above
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5.
Plants help keep humans and other
animals alive.
ffi, Opinion
{3} Fact
7. Plants take in carbon dioxide from the
Which of the following best states the
main idea of the reading passage?
{X} Animals.breathe in oxygen every
day.
{ff'
{n}
Oxygen is an element.
Carbon dioxide is made up of two
elements.
{n} The oxygen-carbon dioxide cycle
keeps the amount of oxygen in the air
fairly constant.
6. We should all grow plants.
{X} Opinion
{S
Fact
8. Humans could not survive without
oxygen.
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4.
To get rid of waste products
To get water
To make their own food
To break down oxygen
Opinion
Fact
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Opinion
Fact
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Respiration
Describe the "cycle" of oxygen and carbon dioxide relating to photosynthesis and cellular respiration.
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