hypothesize why the pores in the cell membrane are differnt sizes?

Answer 1

The pores are designed to let certain molecules in/out of the cell. Thus various sizes will restrict what is allowed to pass through the membrane. The composition of the interior portion of the pore also matters - for example if it's made up of amino acids that are negatively charged then it will better allow neutral or positively charged molecules to pass, but won't allow negatively charged molecules to pass.

Answer 2

probably to let different substances in and out.