What is the primary function of the cell surface membrane?

The cell surface membrane, also known as the plasma membrane, plays a crucial role in maintaining the cell's internal environment. Its primary function is to control the movement of substances into and out of the cell, which is essential for homeostasis. The membrane is selectively permeable, meaning it allows certain molecules to pass while blocking others. This selective control is vital for processes such as nutrient absorption, waste elimination, and communication between cells.

Transport mechanisms such as passive transport, active transport, and various forms of endocytosis and exocytosis depend on the properties of the cell surface membrane, ensuring that essential molecules enter the cell and harmful substances are kept out. In contrast, the other options focus on functions that are either performed by different cellular structures (such as genetic material storage in the nucleus, energy production in the mitochondria, and proteins synthesize by ribosomes) or are not directly related to the role of the cell membrane itself.