The term “cell” was first used by the English naturalist Robert Hooke in
1665 to describe the “great many little boxes” he saw when viewing a
thin slice of cork through a microscope. He derived the word from the
Latin cella, meaning a small room. Hooke was the first scientist to
recognize that living matter was built of basic units rather than of
continuous material.
Today, with the aid of electron microscopes, we
have a more detailed view of living plant and animal cells. Some plant
and animal cells have a particular function and are therefore not all
exactly the same. The cells of animals exis’t in a wide variety of
shapes. They may be round, egg-shaped, square, or rectangular. Some
muscle cells are long and thin, and pointed at each end. Some nerve
cells, with their long branches, resemble trees.
A system of similar
cells forms a tissue for example, nerve cells make up nerve tissue and
combinations of tissues in turn form an organ, such as the brain.
An animal cell (below) is characterized by the various structures within it, chief of which are the nucleus (with its nucleolus), mitochondria, and the folded layers of the endoplasmic reticulum.
Reamde more The animal cell
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