Afunction of a cell membranes in humans is the

The very function, or job of CELL MEMBRANES is to protect the cell from it's surroundings, or in other words, to keep it safe. It controls the movement of substances in and out of cells and organelles, like a guard watching for suspicious activity and protecting something.

The cell membrane itself is a thin, flexible layer around the cells of all living things. It separates the inside of the cells from the outside of the cells.