change, alter, vary, modify mean to make or become different. change implies making either an essential difference often amounting to a loss of original identity or a substitution of one thing for another. changed the shirt for a larger size; alter implies a difference in some particular respect without suggesting loss of identity.
hydrophilic - having a strong affinity for water; tending to dissolve in, mix with, or be wetted by water. chemical science, chemistry - the science of matter; the branch of the natural sciences dealing with the composition of substances and their properties and reactions.
In general, a molecule's size and polarity decides whether it can pass through the bilayer... Lipid bilayer of the cell membrane is composed of phospholipids, which are amphiphilic (that is contains both the hydrophobic and hydrophilic ends). The hydrophilic ends points or heads outwards from the bilayer, whereas the hydrophobic tails point inwards (And towards each other).