"The Living Cell"

Essay by Anonymous UserJunior High, 9th gradeD, November 1996

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The cell is the smallest unit of living matter that can exist by itself. Some plants and animals consist of only a single cell. Others are composed of billions of cells.

Cells exist in a variety of shapes and sizes. They may, for example, be cube- shaped or flat. Scientists who study cells have determined that a single cell may be as large as a tennis ball, or so small that thousands would fit on the period at the end of a sentence on your paper. The yolk of a hen's egg is actually a large cell. By contrast, bacteria- each one of which is a tiny cell- are among the smallest cells. Regardless of its shape or size, every cell contains the 'machinery' to maintain life. While normally cells function with great efficiency, they are subject to various disorders that result in disease.

The size of the cell is usually measured in microns. A micron is a millionth of a meter, and about 25, 000 microns equal one inch. The smallest bacteria are about 0.2 micron in diameter. The average cell in the human body- about ten microns in diameter- is a speck barely visible without the aid of a microscope.

The study of cells is the branch of biology called cytology. The science that deals with cells on the smallest structural and functional level is called molecular biology.

A cell consists of protoplasm, the 'living jelly.' The protoplasm of a typical cell forms three vital parts: The cell membrane, the cytoplasm, and the nucleus.

The membrane encloses the other cell structures. Much of the chemical work of the cell is done in the cytoplasm, which surrounds the nucleus. The nucleus, enclosed by its own membrane, is...