The cell membrane features a structure known as the phospholipid bilayer, which allows for selective permeability. This bilayer consists of two layers of phospholipids, where the hydrophilic (water-attracting) heads face outward, while the hydrophobic (water-repelling) tails face inward. This arrangement enables the membrane to regulate what substances enter and exit the cell, allowing only certain ions and molecules to pass through, thus maintaining the cell's internal environment. Integral and peripheral proteins also play roles in transport and communication.