Final answer:
The plasma membrane is the selective barrier responsible for regulating the entry and exit of substances like nutrients and wastes from the cell. It is selectively permeable, allowing certain materials to pass while blocking others, and is essential for cellular function and survival.
Step-by-step explanation:
The selective barrier that allows the passage of important nutrients and wastes into and out of the cell is known as the plasma membrane. This membrane separates the cell from the external environment and controls the passage of organic molecules, ions, water, oxygen, and wastes. The plasma membrane is selectively permeable, meaning it allows some substances to pass while limiting the entry and exit of others.
Transport across cell membranes is essential for maintaining cellular function. Some substances can passively move in and out of cells, while others require energy-dependent processes, such as the hydrolysis of adenosine triphosphate (ATP). For example, red blood cells expend energy to maintain the balance of sodium and potassium ions and to import essential materials that are crucial for their function. This selectivity is vital for the cell's survival, and losing it could be detrimental to the cell's ability to sustain itself.