Facilitated diffusion involve

Explanation

Facilitated diffusion : The diffusion rate depends on the size of the substances. Obviously smaller substances diffuse faster. The diffusion of any substance across a membrane also depends on its solubility in lipids, which also move faster. Substances that have a hydrophilic moiety find it difficult to move through the membrane. Their movement has to be facilitated by membrane proteins without utilising metabolic energy and there must be concentration gradient. This is called facilitated diffusion. It cannot cause net transport of molecules from low to high concentration, this would require input of energy. Facilitated diffusion is very specific, it allows cell to select substances for uptake. It is sensitive to inhibitors which react with protein side chains.
Some proteins allow diffusion only if two types of molecules move together. In a symport both molecules cross the membrane in the same direction, in an antiport, they move in opposite directions. When a molecule moves across a membrane independent of other molecules, the process is called uniport.