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| Classification
Systems |
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A classification system
lists organisms in a series of groups. Today’s classification
system has
been developed by many
people over many years. In fact, it is
still changing. |
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At
one time, people believed that all living things were either plants
or animals. So scientists divided
all living things into two kingdoms—the plant and animal kingdoms.
A kingdom was
the highest or
most general group of
organisms. Today, a popular system uses six kingdoms,
shown below. |
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Within each
kingdom, scientists compared and contrasted the structures of the
organisms and put
similar organisms into groups. Each group was called a phylum. A phylum was
the next level of
classification
below kingdom.
Scientists then
separated organisms of each
phylum into smaller
groups called classes.
A class was the next level of classification below phylum.
Scientists kept
dividing
each level into smaller
and smaller levels—order, family, and genus—continuing to
the lowest level, called the species. |
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Six Kingdoms of Living Things |
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Archaebacteria
live as single cells.
Many do not need
oxygen or sunlight to live. |
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Eubacteria
are
single cells that
have materials
not found in
archaebacteria. |
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Most protists
are single cells, but some have many cells. Algae are
protists. |
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Mushrooms
and molds are
fungi. Fungi
can
be made of one
or
many cells. |
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Plants
have
many cells
and make their own sugar for food. |
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Animals
have many cells
and get their
food by
eating
other organisms. |
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