Question

the cell membrane is primarily made up of hydrophobic lipids. Urea is a small, hydrophobic moleculemade of carbon, hydrogen, and nitrogen and is a waste product that builds up inside cells. How do these molecules cross the cell membrane to get outside the cell?

Answer 1

Generally put, like dissolves like. Both the lipids in the cell membrane and urea are hydrophobic, so they don't repel each other.