CliffsAP Biology
Chapter One
Cells
Review
Structure and Function of the Cell
The cell is the basic functional unit of all living things. The plasma membrane (cell membrane)
bounds the cell and encloses the nucleus and cytoplasm. The cytoplasm consists of
specialized bodies called organelles suspended in a fluid matrix, the cytosol, which consists of
water and dissolved substances such as proteins and nutrients.
The plasma membrane separates internal metabolic events from the external environment and
controls the movement of materials into and out of the cell. The plasma membrane is a double
phospholipid membrane (lipid bilayer) with the polar hydrophilic heads forming the two outer
faces and the nonpolar hydrophobic tails pointing toward the inside of the membrane
(Figure 2-1).
Proteins are scattered throughout the flexible phospholipid membrane. Proteins may attach
loosely to the inner or outer surface of the membrane (peripheral proteins), or they may extend
into the membrane (integral proteins). Integral proteins may span across the membrane,
appearing at both surfaces (transmembrane proteins). Like phospholipids, integral proteins
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