Which of the following describes a function of the plasma membrane?

The plasma membrane plays a crucial role in controlling the movement of substances into and out of the cell, which is essential for maintaining homeostasis and regulating the internal environment of the cell. It serves as a selective barrier, allowing certain molecules to pass while restricting others, thus ensuring that essential nutrients enter and waste products are removed. This selective permeability is achieved through various mechanisms, including passive transport (like diffusion and osmosis) and active transport processes, which require energy to move substances against their concentration gradient.

While energy production, protein synthesis, and DNA replication are important cellular functions, they are not directly performed by the plasma membrane itself. Energy production occurs primarily in the mitochondria, protein synthesis takes place in ribosomes either free in the cytoplasm or attached to the endoplasmic reticulum, and DNA replication occurs in the nucleus. Thus, controlling substance movement is the primary function of the plasma membrane, making it the correct choice.