Multiple Choice
Which statement best differentiates passive transport from active transport across a cell membrane?
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9. Transport Across Membranes
Principles of Transmembrane Transport
Multiple Choice
Which of the following is an example of active transport across a cell membrane?
A
Water moving across the membrane through aquaporins in response to an osmotic gradient
B
Oxygen diffusing directly through the lipid bilayer from high to low concentration
C
Glucose entering a cell through a GLUT transporter 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
Step 1: Understand the difference between passive and active transport. Passive transport moves substances down their concentration gradient without energy input, while active transport requires energy to move substances against their gradient.
Step 2: Analyze each option to determine if energy is required and if the movement is against the concentration gradient.
Step 3: Recognize that water moving through aquaporins and oxygen diffusing through the lipid bilayer are examples of passive transport because they move down their concentration gradients without energy.
Step 4: Note that glucose entering via a GLUT transporter is facilitated diffusion, a type of passive transport, since it moves glucose down its concentration gradient without ATP.
Step 5: Identify that the Na+/K+ ATPase uses ATP hydrolysis to pump Na+ out and K+ into the cell against their concentration gradients, which is a classic example of active transport.
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