Question

What happens during the process of facilitated diffusion?

Answer 1

Facilitated diffusion is a passive transport process in which substances move across the plasma membrane with the help of transport proteins. This allows polar molecules and ions that are not soluble in the hydrophobic lipid bilayer to diffuse into or out of the cell following their concentration gradient without the cell expending energy.

Step-by-step explanation:

Facilitated Diffusion Explained

Facilitated diffusion is a type of passive transport that allows substances to move across the cell (plasma) membrane down their concentration gradient. However, unlike simple diffusion, it involves transport proteins such as channel proteins and carrier proteins because these substances are usually polar molecules or ions that are repelled by the hydrophobic interior of the lipid bilayer.

During facilitated diffusion, the substance will bind to a specific carrier protein, or pass through a channel protein, effectively being 'shielded' from the hydrophobic parts of the membrane. This assistance enables the substance to move from an area of higher concentration to an area of lower concentration without the cell expending energy. This process is also characterized by a saturation point similar to enzyme catalysis, indicating that once all the available transport proteins are occupied, the rate of diffusion will not increase further, regardless of the concentration gradient.

Symport and antiport systems illustrate cases where two different substances use the same transport protein simultaneously, either moving in the same direction (symport) or in opposite directions (antiport).

Answer 2

This is where diffusion happens down the concentration gradient i.e. from high to low concentrations (just like simple diffusion) but facilitated diffusion requires a special and specific protein within the cell membrane. The substate binds to the receptor and the receptor itself changes conformation so that the substrate is now on the other side of the membrane. This is done for molecules that are too large to pass straight through the phospholipid bilayer (cell membrane) by simple diffusion e.g. glucose.