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Bacteria
consist of only a single
cell, Bacteria have
been found that can
live in temperatures
above the boiling point
and in cold that would
freeze blood. They "eat"
everything from sugar
and starch to sunlight,
sulfur and iron.
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Classification
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Bacteria
fall into a category of life
called the Prokaryotes. Prokaryotes'
genetic material, or DNA,
is not enclosed in a cellular
compartment called the nucleus.
Bacteria and archaea are the
only prokaryotes. All other
life forms are Eukaryotes,
creatures whose cells have
nuclei. (Note: viruses are
not considered true cells,
so they don't fit into either
of these categories.)
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Early
Origins
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Bacteria
are among the earliest forms of
life that appeared on Earth billions
of years ago. Scientists think that
they helped shape and change the
young planet's environment, eventually
creating atmospheric oxygen that
enabled other, more complex life
forms to develop. Many believe that
more complex cells developed as
once free-living bacteria took up
residence in other cells, eventually
becoming the organelles in modern
complex cells. The mitochondria
that make energy for your body cells
is one example of such an organelle.
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What
They Look Like
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There
are thousands of species of
bacteria, but all of them
are basically one of three
different shapes. Some are
rod- or stick-shaped and called
bacilli. Others are shaped
like little balls and called
cocci. Others still are helical
or spiral in shape, like the
Borrelia pictured at the top
of this page. Some bacterial
cells exist as individuals
while others cluster together
to form pairs, chains, squares
or other groupings.
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Ball-shaped
Streptococci
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Where
They're Found
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Bacteria
live on or in just about every
material and environment on
Earth from soil to water to
air, and from your house to
arctic ice to volcanic vents.
Each square centimeter of
your skin averages about 100,000
bacteria. A single teaspoon
of topsoil contains more than
a billion (1,000,000,000)
bacteria.
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How
They Move
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Some
bacteria move about their
environment by means of long,
whip-like structures called
flagella. They rotate their
flagella like tiny outboard
motors to propel themselves
through liquid environments.
They may also reverse the
direction in which their flagella
rotate so that they tumble
about in one place. Other
bacteria secrete a slime layer
and ooze over surfaces like
slugs. Others are fairly stationary.
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What
They Eat
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Some
bacteria are photosynthetic —they
can make their own food from sunlight,
just like plants. Also like plants,
they give off oxygen. Other bacteria
absorb food from the material they
live on or in. Some of these bacteria
can live off unusual "foods" such
as iron or sulfur. The microbes
that live in your gut absorb nutrients
from the digested food you've eaten.
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