Which two factors of a molecule determine whether or not iit can cross the membrane

Two factors determine whether a molecule will cross a membrane:

1. the permeability of the molecule in a lipid bilayer and

2. the availability of an energy source.

The size, polarity, and charge of a substance will determine whether or not the substance can cross the cell membrane by diffusion. The cholesterol was an example of lipid and is highly soluble in the nonpolar environment of the lipid bilayer.