Simple Diffusion Across the Cell (Plasma) Membrane. The structure of the lipid bi-layer allows small, uncharged substances such as oxygen and carbon dioxide, and hydrophobic molecules such as lipids, to pass through the cell membrane, down their concentration gradient, by simple diffusion.
Low air pressure is usually associated with D. Cloudy, wet weather.
A theory is a hypothesis that someone had but has not proven it.
A law is something that is proved.
Example: Sir Issac Newton had a theory on gravity he sat under a tree and then had a conclusion.
