Here's why:
* Passive Transport: Facilitated diffusion is a type of passive transport, meaning it doesn't require the cell to expend energy (ATP). This is because the movement of molecules is driven by the concentration gradient – molecules move from an area of high concentration to an area of low concentration.
* Carrier Proteins: Carrier proteins act as "helpers" to facilitate the movement of molecules across the membrane. They bind to the molecules on one side of the membrane, change their shape, and release the molecules on the other side. This process helps molecules that are too large or polar to cross the membrane on their own to still move down their concentration gradient.
Key points to remember about facilitated diffusion:
* Down the concentration gradient: Movement always occurs from high to low concentration.
* Specific binding: Carrier proteins are specific for the molecules they transport.
* Saturable: The rate of transport can be saturated if the concentration of the molecule is very high, as all the carrier proteins become occupied.
Examples of molecules transported via facilitated diffusion:
* Glucose
* Amino acids
* Some ions
