Final answer:
The primary function of the cell membrane is to control the entrance and exit of substances, maintaining the internal environment of the cell. It is selectively permeable, which is essential for cell survival and communication.
Step-by-step explanation:
Primary Function of the Cell Membrane
One primary function of the cell membrane is to regulate the movement of substances in and out of the cell; it acts as a selective barrier. The cell membrane's selectivity is crucial for maintaining the cell's proper balance of nutrients, ions, and organic molecules, which is essential for its survival. It is selectively permeable, a feature that allows certain substances to pass through freely while others require special transport proteins or additional energy to cross. Furthermore, the cell membrane plays a significant role in cell communication and adhesion, impacting tissue and organ formation as well as recognizing 'self' versus 'non-self' for the immune response.
The plasma membrane's flexibility is vital for the functionality of cells such as red blood cells and white blood cells, which must change shape to navigate through narrow capillaries. This flexibility is not only crucial for individual cell function but also for the overall integrity and coordination within multicellular organisms.