What is the main function of the cell membrane?

The primary function of the cell membrane is to provide selective permeability, which is crucial for maintaining the cell's internal environment. This means that the cell membrane regulates which substances can enter or exit the cell, thereby allowing essential nutrients in while keeping harmful substances out. This selective barrier helps maintain homeostasis, the stable internal conditions necessary for the cell to function properly.

While the other functions mentioned are important for overall cell function, they do not encapsulate the main role of the cell membrane as effectively. For example, generating energy typically takes place in the mitochondria, and storing genetic information is the role of the nucleus. Providing structure and facilitating communication are also significant aspects of the cell's operation, but they are not the defining characteristic of the cell membrane itself. The essence of the cell membrane's function lies in its ability to selectively manage the movement of materials, making it fundamental to cellular life.