Facilitated diffusion occurs when molecules pass through a cell membrane via special proteins. This process typically involves molecules that are either too large or polar, which makes it difficult for them to pass through the lipid bilayer of the cell membrane. Some common examples of these molecules include:
- Glucose: This sugar molecule is a primary energy source for cells, and due to its size and polar nature, it cannot freely cross the membrane. Instead, it uses transport proteins called GLUT transporters to facilitate its movement.
- Amino Acids: Building blocks of proteins, amino acids are also often polar or charged, making them unable to diffuse through the lipid bilayer without help.
- Ions: Charged particles, such as sodium (Na+) and potassium (K+), rely on specialized ion channels or transporters to move across the membrane.
In summary, facilitated diffusion is crucial for the transport of large or polar molecules and ions across cell membranes, allowing cells to uptake essential nutrients and maintain proper function.