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Put your eyes closed and visualize a brick wall. What constitutes the foundation of that wall? Of
course, it is just a single brick. Your body is made up
of fundamental building blocks,
much like a brick wall,
and those building blocks are called cells. Each type of cell in your body is specialized for a particular
function. The human body is built from a
variety of cell types, just as a house is built from different building
materials. For instance, epithelial cells line the body's cavities and protect its external organs.
The body is
supported and protected in part by bone cells. Immune system cells combat invasive bacteria.
Red blood cells
also transport oxygen throughout the body. Each of these cell types is essential to the body's growth,
development, and ongoing maintenance. Despite their extreme
diversity, all cells have some
universal traits
in common. The smallest component of a living thing is a cell. A living thing, like you, is called
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