Multiple Choice
Active transport is different from simple diffusion because active transport:
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9. Transport Across Membranes
Principles of Transmembrane Transport
Multiple Choice
Which of the following is an example of primary active transport across a cell membrane?
A
Osmosis of water through aquaporin channels driven by a water potential difference
B
Facilitated diffusion of glucose into a cell through a GLUT transporter down its concentration gradient
C
Simple diffusion of O2 across the lipid bilayer down its concentration gradient
D
The Na+/K+ ATPase pumping Na+ out of the cell and K+ into the cell using ATP hydrolysis
Verified step by step guidance1
Understand the definition of primary active transport: it is the movement of molecules across a membrane against their concentration gradient using energy directly from ATP hydrolysis.
Review each option and identify whether it involves movement against a concentration gradient and whether it uses ATP directly.
Osmosis of water through aquaporin channels is passive transport driven by water potential differences, not requiring ATP, so it is not primary active transport.
Facilitated diffusion of glucose through GLUT transporters occurs down the concentration gradient without ATP, so it is a form of passive transport.
Simple diffusion of O2 across the lipid bilayer is passive movement down its concentration gradient without energy input.
The Na+/K+ ATPase uses ATP hydrolysis to pump Na+ out and K+ into the cell against their concentration gradients, which fits the definition of primary active transport.
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