Final answer:
Cell membranes are selectively permeable and composed of a double layer of phospholipids embedded with proteins.
Step-by-step explanation:
The cell membrane is selectively permeable, meaning only some molecules can get through. It is composed of a double layer of phospholipids embedded with proteins. The phospholipids have a hydrophilic head and a hydrophobic tail, which allows the membrane to be both flexible and selectively permeable.