About Cells Essay

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About Cells Cell, smallest unit of an organism that can function independently. All living organisms are made of cells, and it is generally held that nothing less than a cell can truly be said to be alive. Some microscopic organisms, such as bacteria and protozoa, are single cells whereas animals and plants are composed of many millions of cells assembled into tissues and organs. Although viruses and cell-free extracts are able to perform many individual functions of a living cell, they lack the capacity shown by cells of independent survival, growth, and replication and are therefore not considered…show more content…
All cells host a variety of chemical reactions that enable them to grow, produce energy, and eliminate waste. Together these reactions are termed metabolism (from a Greek word meaning "change"). All cells contain hereditary information, encoded in molecules of deoxyribonucleic acid (DNA), that directs the cell's activities and enables it to reproduce, passing on its characteristics to its offspring. These and other numerous similarities (including many identical or nearly identical molecules) demonstrate that there is an unbroken continuity between modern cells and the first primitive cells that appeared on Earth.

Chemical Composition

There is nothing in living organisms that contravenes chemical and physical laws. The chemistry of life, the subject of biochemistry, is based overwhelmingly on carbon compounds and almost exclusively on chemical reactions that take place in aqueous solution in a narrow range of temperatures-those experienced on Earth. The chemistry of living organisms is much more complicated than any other chemical system known. It is dominated and coordinated by enormous polymers-molecules made from chains of linked chemical subunits-the unique properties of which enable cells and organisms to grow, reproduce, and so on. These large polymeric molecules, or
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