what are cell membranes made up of?
Rating Newest Oldest. Best Answer: The cell membrane is made up mostly of molecules called phospholipids. Lipids, as you may know, are any organic molecule that won't mix with water. Cooking oil, for example, is made up of lipids. Lipids are used in the cell membrane precisely because they won't mix with water, meaning they form an effective barrier between the water solution inside the cell and the environment outside.