Active and passive transport mechanisms

PASSIVE:

Substances move through the plasma membrane in essentially two ways- passively or actively.

In passive processes substances cross the membrane without any energy input from the cell. Two main types of passive transport ante diffusion and filtration. The driving energy source for diffusion is the kinetic energy of the molecules themselves. Substances transported in simple diffusion include oxygen,carbon dioxide,fat-soluble vitamins,& alcohol. Substances transported in facilitated diffusion include glucose and other sugars,amino acids,& ions. A carriers a transmembrane integral protein that shows specificity for molecules of a certain polar substance or class of substances that are too large to pass through membrane channels(sugars & amino acids). It first envelopes then releases the transported substance, shielding it en route from nonpolar regions of the membrane. Channels are transmembrane proteins that serve to transport substances, usually ions or water, through aqueous channels from one side of the membrane to the other. Like diffusion, filtration involves a gradient, however, the gradient for this is a pressure gradient. This means it pushes solute containing fluid(s) from a higher-pressure area to a lower pressure area.