What types of molecules need more to get through the cell membrane what them get through?

Water diffusion is called osmosis. Oxygen is a small molecule and it's nonpolar, so it easily passes through a cell membrane. Carbon dioxide, the byproduct of cell respiration, is small enough to readily diffuse out of a cell. Small uncharged lipid molecules can pass through the lipid innards of the membrane.

Yes he thought they should be left to chance why, because he thought that was the best thing to do