Biology  5/e   Raven/Johnson
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Just as we do not know exactly when life began, we do not know exactly what shape it first assumed. We don't even know if it had a specific shape or was amorphous. Ultimately, however, life was packaged in structures we now call cells.

Even the simplest and smallest of cells must be able to communicate and cope with its environment to survive, grow, and reproduce. It is awesome to contemplate that the tiny microscopic specks we call bacteria must perform all of life's functions. Cells can perform their functions so well that some can defeat our bodies' defenses and cause considerable bodily harm--even death. Bacteria are the simplest of cells. Because they are so simple, lacking even a nucleus, we call them prokaryotes.

More complex cells including the ones making up our own bodies, are called eukaryotes. There are many structures that distinguish the eukaryotes, but the name is derived from the possession of nuclei.. The cells in their great variety display both a commonality and diversity of structures. Such commonality and diversity of structures by which cells perform remarkable feats is the substance of this chapter.

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