Here's a breakdown:

* Diffusion: The movement of molecules from an area of high concentration to an area of low concentration. This happens naturally due to the random movement of molecules.

* Concentration gradient: The difference in concentration of a substance between two areas.

* Membrane-bound carrier proteins: Proteins embedded in the cell membrane that can bind to specific molecules and facilitate their transport across the membrane.

* Facilitated diffusion: A type of passive transport where molecules move across the cell membrane with the help of carrier proteins, but without the need for energy input.

Here's how it works:

1. Binding: The molecule (like glucose) binds to the carrier protein on one side of the membrane.

2. Conformational change: The carrier protein undergoes a change in shape, allowing the molecule to be transported across the membrane.

3. Release: The molecule is released on the other side of the membrane, where its concentration is lower.

4. Carrier protein returns to original shape: The carrier protein reverts back to its original conformation, ready to bind another molecule.

Key points to remember:

* Facilitated diffusion is a passive process, meaning it does not require energy from the cell.

* It follows the concentration gradient, meaning molecules move from an area of high concentration to an area of low concentration.

* It is specific, meaning that each carrier protein typically binds to only one type of molecule.

Examples of molecules transported by facilitated diffusion:

* Glucose

* Amino acids

* Ions (like sodium and potassium)