Cellular Basics

Historical Views of Cells

What is a cell?

In general, a cell is the basic unit of all forms of life. Cells are considered to be specialized depending on their function, such as tissue cells, cells of the various animal organs, or even the cells that create a tomato plant. They can range in size from microscopic to the size of a chicken egg. In addition, an organism can be only one cell (single-celled) or multicelled, such as a human—an organism with more than 100,000,000,000,000 cells. (For more about humans and cells, see the chapter “Biology and You.”)


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