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Oxygen Cycle
Required for Life

All living things use oxygen or depend on
organisms that use oxygen in some way.
All Animals and Other Consumers
Use Oxygen

We use oxygen to break down simple
sugar and release energy.

This can be done through respiration or
fermentation.

Animals mainly use respiration.
Respiration

The process that breaks apart simple food
molecules to release energy.

It occurs inside cells.

What YOU do with the oxygen you take in.
Simple Sugar — Glucose
The molecule most living things use for
energy — including us!

We break down food into smaller molecules
during digestion. One of the small molecules is
glucose.

Glucose leaves your intestines, goes into your
blood and is taken to every cell in your body.
Respiration in Cells

In your cells, oxygen is used to split
glucose apart — releasing energy, water
and carbon dioxide.
Photosynthesis

Plants take in carbon dioxide and water
and use them to make food. Their food is
simple sugar — glucose.
Photosynthesis (continued)

Plants pull the carbon off CO2 and use the
carbon in glucose. (They do not need the oxygen for this. They
get that from water, H2O.)

Plants release the oxygen (O2) back into the
atmosphere.

Other organisms use the free oxygen for
respiration.
How are photosynthesis and
cellular respiration similar?


Photosynthesis uses carbon dioxide and
produces oxygen.

Cellular respiration uses oxygen and produces
carbon dioxide.
Basic idea
Rabbit gives off CO2,
which is taken in by the plant.
Rabbit eats food,
breaks it down
and releases
CO2.
Plant uses CO2
to make food.
Plant gives off O2,
which is taken in by the rabbit.
Everywhere

This happens on land and in the water.

Algae and aquatic plants produce food
underwater through photosynthesis.

They use CO2 dissolved in the water.

Other aquatic organisms use the dissolved
oxygen these plants release into the water.
Respiration
Photosynthesis
Kind of a C-on/C-off Cycle

Plants take the carbon off the CO2, freeing the
oxygen so it can be used for respiration.

During respiration, organisms attach a carbon to
the O2 and release CO2 so it can be used for
photosynthesis.

One big cycle — all living things depend on each
other for it to work!
Human Impact

We keep destroying natural areas, especially
forested areas with many plants and replacing
them with buildings, parking lots, lawns, etc.

Fewer plants mean less oxygen and more
carbon dioxide.

This disturbs the balance of the natural cycle.
More Human Impact

Every time something burns (combustion),
more carbon dioxide is released into the
atmosphere.

We add more and more CO2 and destroy
more and more of the plants that clean
the air for us.
What We Need to Do

Stop destroying and promote regrowth of
natural areas — especially forests.

Burn less (fossil fuels, forest fires, etc.)