Question about plasma membranes.... I read this online and am wondering if this is true. It said that - "When you think about a membrane, imagine it is like a big plastic bag with some tiny holes. That bag holds all of the cell pieces and fluids inside the cell and keeps any nasty things outside the cell. The holes are there to let some things move in and out of the cell." How can a cell membrane hold it's contents inside if it has holes in it like a big plastic bag, even if they were tiny? Does a cell membrane really have holes?