Which of the following choices correctly describes the composition of the cell membrane?

The correct choice is "contains lipids and proteins." The cell membrane is the outermost layer of the cell that separates the internal environment of the cell from the external environment. It is composed mainly of two types of molecules: lipids and proteins. The lipids in the cell membrane are primarily phospholipids, which have a hydrophilic (water-loving) head and a hydrophobic (water-fearing) tail. These lipids are arranged in a bilayer, with the hydrophobic tails facing each other and the hydrophilic heads facing outward towards the watery environments on either side of the membrane. The proteins in the cell membrane serve a variety of functions, including transport of molecules across the membrane, cell signaling, and structural support. Some proteins span the entire membrane, while others are only present on one side. The cell membrane also contains small amounts of carbohydrates and other molecules, but lipids and proteins are the two main components.