Final answer:
The cell's transportation system is the cell membrane, which acts as a semi-permeable barrier and controls the movement of substances into and out of the cell. Transport proteins within the membrane facilitate the movement of specific substances. so, option b is the correct answer.
Step-by-step explanation:
The cell's transportation system is the cell membrane.
The cell membrane is a semi-permeable barrier that surrounds the cell and controls the movement of substances into and out of the cell. It acts as a transportation system by allowing certain molecules to pass through while keeping others out. Transport proteins within the cell membrane help facilitate the movement of specific substances.
For example, carrier proteins can transport molecules across the cell membrane by changing their shape and allowing the molecules to pass through. Ion channels act as tunnels, allowing ions to move across the membrane through a pore. These transport proteins are essential for maintaining homeostasis and ensuring that the cell receives the necessary nutrients and removes waste products.