Question

What does a cell membrane let through?

Answer 1

Cell Membrane is a semi permeable membrane so it only allows materials which are allowed to go inside by the lipid layer.

Explanation:

It allows smaller, non-polar and non-charged molecules through such as `O_2, CO_2` etc. The diffusion of water through the membrane is called osmosis.

However, it doesn't allow charged molecules (such as K+, Na+, H+) or larger molecules such as glucose (`C_6H_12O_6`) directly through the bilayer; instead these must go through protein channels.

Hope this helps!