Conversation so far:
where does facilitated diffusion occur in the cell membrane
Facilitated diffusion occurs in the cell body.
what is the definition of diffusion?
Diffusion is the net movement of anything from a region of higher concentration to a region of lower concentration.
How is a cell membrane composed?
Plant cell membranes are rigid walls, and animal cell membranes are lipid bilayers.
What are lipid bilayers in cell membranes?
The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around cells.

Question: what is the purpose of the fats in the bilayers
Self-contained rewrite: What is the purpose of lipids in regards to cell membranes?