Cellular Transport Processes Across Membranes

Steps:

• Recall active transport uses energy to move substances against concentration gradients into or out of cells.
• Identify facilitated diffusion as passive movement of substances through carrier proteins or channels, allowing entry or exit down gradients.
• Define osmosis as passive water movement across semi-permeable membranes, transporting water into or out of cells.
• Confirm all three processes involve crossing the cell membrane, enabling transport in both directions.

Why A is correct:

• All three—active transport, facilitated diffusion, and osmosis—directly facilitate substance movement across the plasma membrane, as per cell biology definitions of membrane transport.

Why the others are wrong:

• B excludes osmosis, but osmosis transports water across membranes.
• C excludes facilitated diffusion, which moves ions and molecules via proteins.
• D excludes active transport, which moves substances against gradients using ATP.

Final answer: A