The membrane of the cell is made of phospholipid bilayer.
There are proteins which go thru the membrane.
could you please explain this further, are you saying that the polar molecules and ions cant enter because the membrane keeps them out? i belive that is what you are saying, if so how do the food particles get through.
The membrane is a chain-linked fence. Only really small molecules can pass thru while big molecules can’t. To remedy this, the fence has special passages(gates) that allow bigger stuff in(see James’s post).