Cell membranes maintain homeostasis by regulating what enters and leaves cells through their selectively permeable membrane. They are composed of...

Cell membranes maintain homeostasis by regulating what enters and leaves cells through their selectively permeable membrane. They are composed of phospholipids, proteins, and cholesterol. What characteristic of phospholipids makes them essential components of cell membranes? Why is the hydrophilic end of phospholipids attracted to water? Explain why sterols, like cholesterol, can add "stiffness" to membranes that contain them.