Here's why:

* Facilitated diffusion is a type of passive transport, meaning it doesn't require energy from the cell. However, unlike simple diffusion, it does require the assistance of a protein.

* Transport proteins are embedded within the cell membrane and act as channels or carriers for specific molecules.

* These proteins can bind to the molecule they're transporting, changing their shape to move the molecule across the membrane.

Here's a breakdown of how facilitated diffusion works:

1. The molecule binds to the transport protein.

2. The transport protein changes shape, moving the molecule across the membrane.

3. The molecule is released on the other side of the membrane.

Key takeaways:

* Facilitated diffusion is still passive transport, meaning it doesn't require energy.

* The transport protein acts as a facilitator, allowing the molecule to cross the membrane that it wouldn't otherwise be able to.

* This process is highly specific, with each type of transport protein only binding to and transporting certain types of molecules.