Final answer:
The semipermeable outer boundary of the cell's protoplasm is called the plasma membrane or cell membrane. It controls the movement of substances into and out of the cell, allowing certain substances to pass through while keeping others in or out.
Step-by-step explanation:
The semipermeable outer boundary of the cell's protoplasm is called the plasma membrane or cell membrane. It separates the cell from the external environment and controls the passage of organic molecules, ions, water, oxygen, and wastes into and out of the cell. The plasma membrane is selectively permeable or semipermeable, allowing certain substances to pass through while keeping others in or out.