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He couldn’t see the cells very well, Today we know that those things
because his microscope wasn’t as are bacteria. Think about that the
good as the microscopes we have next time you are brushing your
today. But his discovery is still teeth! (There are cool experiments
very important, because it helped that relate to this in the activities
us to understand that living things section!)
are made of cells.
By the middle of the 1800’s,
several other scientists had studied
cells, and this work led to a theory.
Another scientist who looked at
In science, a theory is a group of
cells was Anton van Leeuwenhoek.
ideas that explains why or how
Leeuwenhoek’s microscope was
something happens. The cell
almost as good as the microscopes
theory says three things. These
we use to look at cells today, and
three things are:
he saw lots of things nobody had
seen before. He saw animals that 1. All living things are made of
had never been seen. No one had one or more cells
seen them because they were too 2. All of the activities needed
small to see with just your eyes. for life happen in cells
He also saw the cells that make up 3. All cells come from other
human blood. Leeuwenhoek even cells
did an experiment where he
The cell theory is a very important
scraped the plaque off his teeth
part of biology, which is the study
and looked at it under his
of life.
microscope. When he looked at
the plaque, Leeuwenhoek saw tiny
living things.
Cell Shape and Size
In order for your city or town to
survive, people need to do different
jobs. Police officers, construction
workers, teachers, doctors, and fire
fighters all do certain things to
make sure everything runs
smoothly. The different cells of
your body also do different jobs
Van Leeuwenhoek drew these sketches of what he
that make things run smoothly in
saw from the plaque in his mouth
your body. In fact, you have
trillions of cells, and each one plays
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