National League for Nursing (NLN) Science Practice Exam

What is the role of the plasma membrane in a cell?

1. Energy production

2. Cellular respiration

3. Regulating what enters and exits the cell

4. Synthesis of proteins

The correct answer is: Regulating what enters and exits the cell

The role of the plasma membrane in a cell primarily revolves around regulating what enters and exits the cell, making the choice regarding this function the most accurate. The plasma membrane acts as a selective barrier that controls the movement of ions, molecules, and nutrients in and out of the cell, maintaining homeostasis and the internal environment necessary for cellular function. This selective permeability is crucial for the survival of the cell, as it ensures that essential substances such as nutrients can enter the cell while waste products can be removed. In addition to its regulatory function, the plasma membrane also plays a critical role in cell signaling and communication with the external environment, owing to the presence of various receptors and proteins embedded within it. These features enable cells to respond to changes in their surroundings effectively. The other options, while important cellular functions, do not directly correlate with the primary role of the plasma membrane. Energy production is typically associated with organelles like mitochondria. Cellular respiration is a process that occurs within cells but is not performed by the plasma membrane itself. The synthesis of proteins predominantly takes place in the ribosomes and endoplasmic reticulum, rather than at the membrane level. Thus, the answer correctly identifies the essential regulatory function of the plasma membrane in cellular operations.