Diffusion Through the Membrane

The cell membrane has the ability to selectively regulate materials that go into and out of the cell. The membrane has both passive and active roles in transporting materials into and out of the cell. Passive transport occurs when molecules move from an area of high concentration to an area of low concentration (down the concentration gradient). Passive transport does NOT require the cell to use any energy (ATP). IF the individual molecules of a substance are smaller than the pores of the membrane, than diffusion across the membrane can occur. Remember: diffusion is a natural “spreading-out” process that is a result of molecules constantly being in motion. Diffusion occurs until a dynamic equilibrium is reached.

Check this link out to see an animation of diffusion towards a dynamic equilibrium.

Active transport occurs when molecules move from an area of low concentration to an area of high concentration (against the concentration gradient). Active transport requires the cell to use energy (ATP) in order to occur. Active transport can also occur when a molecule that is too large to fit through the pores needs to be transported across the membrane.

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