Biology  5/e   Raven/Johnson
	Student   Online Learning Center

Membranes may be more than mere containers. The plasma membrane, for instance, is far more complex in function. Complex function calls for complex structure. While a cell is somewhat at the mercy of its environment, it has ways of coping with that environment. Membrane structures enable the cell to regulate the flow of materials in and out of itself. The cell can, by virtue of its membrane structures, sense the characteristics of the environment and identify substances in it. Cells may also identify other cells and identify themselves to those other cells. The membrane is, in many ways, the key to the survival and flourishing of a cell.

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