Final answer:
Cell membranes are selectively permeable, allowing only certain substances to pass through while restricting others. The structure of the cell membrane contributes to this selectivity.
Step-by-step explanation:
Cell membranes are selectively permeable, meaning that they allow certain substances to pass through while restricting the passage of others. This is crucial for maintaining homeostasis and regulating the internal environment of cells. The structure of the cell membrane, composed of a phospholipid bilayer with embedded proteins, plays a critical role in this selective permeability.
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