What is more acceptable?
There are more sodium ions outside the cell
or
There are more sodium ions outside of the cell
English Language Learners Stack Exchange is a question and answer site for speakers of other languages learning English. It only takes a minute to sign up.
Sign up to join this communityWhat is more acceptable?
There are more sodium ions outside the cell
or
There are more sodium ions outside of the cell
outside the cell
outside of the cell
on the outside of the cell
of these three only "on the outside of the cell" might imply direct contact with the cell wall.
Since you are probably talking about osmotic pressure, any of the three can be used without loss of understanding since the reader will probably already know how osmotic pressure works.