Movement Across the Cell Membrane and Membrane Potentials

After you have completed this section of the chapter, you should be able to meet the following objectives:

♦ Discuss the mechanisms of membrane transport
associated with diffusion, osmosis, endocytosis, and
exocytosis and compare with active transport
mechanisms

♦ Describe the function of ion channels

♦ Describe the basis for membrane potentials

♦ Explain the relationship between membrane
permeability and membrane potential

The cell membrane serves as a barrier that controls which substances enter and leave the cell. This barrier function allows materials that are essential for cell func­tion to enter the cell, while excluding those that are harm­ful. It is responsible for differences in the composition of intracellular and extracellular fluids.