Detailed Instructions: Given a scientific passage and an answer, generate a question for the given answer.
Q: Passage: The cell membrane is a thin coat of phospholipids that surrounds the cell. It's like the "skin" of the cell. It forms a physical boundary between the contents of the cell and the environment outside the cell. It also controls what enters and leaves the cell. The cell membrane is sometimes called the plasma membrane. Answer: cell membrane
A:
What is the thin coat of phospholipids that surrounds the cell and controls what enters and leaves?