How the inside of a cell remains separated from its environment?

Answer 1

when phospholipids are arranged in a way that polar heads can be closest to water molecules and the nonpolar molecues tails can be found away from the water molecules. when phospholipid molecules come toghether in this way a barrier is created that is polar at that surface and non polar in the middle. Water substances will not move easily through the plasma because they are stopped by the non polar middle. Therefore, the plasma membarane can separate the enovironmet insde the cell from the environment outside the cell.