Everything classified as living is made of cells. The two main divisions
of cells are plant cells and animal cells. Animal cells include blood cells, bone cells, muscle cells, nerve cells, and skin cells.
blood cells
Although the human body contains over 75 trillion cells, the majority
of life forms exist as single cells that perform all the functions necessary
for independent existence. Most cells are far too small to be seen with
the naked eye and require the use of high-power optical and electron
microscopes for careful examination.
Until the mid-seventeenth century, scientists were unaware that cells
even existed. It wasn't until 1665 that biologist Robert Hooke observed
through his microscope that plant tissues were divided into tiny
compartments, which he called cells. It took another 175 years,
however, before scientists began to understand the true importance
of cells.
For more information on different types of cells, click on one
of the choices below.
animal cells
Cell links
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