1. Regulation of transport: The plasma membrane acts as a selective barrier, controlling the movement of substances into and out of the cell. This is crucial for maintaining the cell's internal environment, ensuring that essential nutrients are taken in, waste products are removed, and the proper balance of ions is maintained. This regulation is achieved through various mechanisms like diffusion, osmosis, active transport, and endocytosis/exocytosis.

2. Cell signaling and communication: The plasma membrane is studded with receptors that bind to specific molecules outside the cell. This binding triggers a chain of events within the cell, leading to various responses like changes in gene expression, protein activity, or cell movement. This ability to sense and respond to its environment allows the cell to interact with other cells, receive signals from hormones and neurotransmitters, and adapt to changing conditions.

These two functions are interconnected, as the ability to regulate transport is essential for the cell to receive and respond to signals from its environment. The plasma membrane is therefore a dynamic and essential structure that plays a critical role in the survival and function of all cells.