What is the primary role of the cell membrane?

The primary role of the cell membrane is to control the substances that enter and leave the cell. This selective permeability is essential for maintaining the internal environment of the cell, allowing it to regulate ion concentrations, nutrients, and waste products. The cell membrane is composed of a phospholipid bilayer with embedded proteins, which facilitate the transport of various molecules through the membrane. This dynamic structure allows the cell to interact with its environment in a controlled manner, ensuring that necessary substances can enter while potentially harmful substances are kept out.

Moreover, the ability to transport materials across the membrane is vital for processes such as signaling, nutrient uptake, and waste removal, all of which are crucial for the cell's survival and function. The other options, while related to cellular functions, do not capture the primary and essential role of the cell membrane in regulating the internal environment of the cell.