The animal cell

 


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.

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