Question

How do molecules pass through the cell membrane?

Answer 1

There are several methods for this to happen depending on the type of the molecule and the concentration gradient. The processes that are included are:
Diffusion, simple and facilitated.
Osmosis.
Active uptake.
Endo and exocytosis.

Explanation:

Simple diffusion happens down concentration gradient for small non polar and uncharged molecules, and for the lipid soluble ones.
Facilitated happens also down concentration gradient but for polar or charged molecules.
Both are passive which means they do not require energy.
Osmosis is for water transport down water potential gradient.
Active uptake is for small molecules going against concentration gradient, and it needs energy.
Endocytosis is for getting big molecules inside the cell with the aid of a vesicle, and exocytosis is to get big molecules outside the cell also with the aid of a vesicle. Both need energy.