A cell membrane has consists of phospholipids. They are lipids with a phosphate group such as (PO3/4). They are hydrophilic meaning that they allow water to pass through proteins well some at least- but it might be needed to move molecules throughnthe membrane as well. But basically it's just a composed bilayer of phospholipids with hydrophobic acid tails so that they could all meet with one another. The form complexes into function to describe or to identify the cells to anothers cells.
Hope this helps.
Gravity can be such a tricky subject to talk about I wish I could answer this I need to study more
