What function does the plasma membrane serve in a cell?

The plasma membrane plays a crucial role in maintaining the internal environment of a cell by regulating what enters and exits. It is primarily composed of a phospholipid bilayer that is embedded with proteins, cholesterol, and carbohydrates, making it selectively permeable. This selectivity ensures that essential nutrients can pass into the cell while waste products and harmful substances are kept out or removed.

By controlling the movement of ions, molecules, and information in and out of the cell, the plasma membrane helps maintain homeostasis, which is vital for the cell's survival and function. This regulatory function supports various cellular activities and responses, ultimately contributing to the overall health and functionality of the organism.

The other options relate to functions that are carried out by other cellular structures. For instance, photosynthesis is conducted by chloroplasts in plant cells, genetic material is stored in the nucleus, and cellular respiration occurs within the mitochondria.