Multiple Choice
Which of the following is the best definition of active transport across a biological membrane?
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9. Transport Across Membranes
Principles of Transmembrane Transport
Multiple Choice
Which of the following is a form of active transmembrane transport (requires energy input)?
A
Na+ uptake driven by the Na+/K+ ATPase (a primary active transport pump)
B
Simple diffusion of O2 across the lipid bilayer
C
Facilitated diffusion of glucose through a GLUT transporter down its concentration gradient
D
Osmosis of water through aquaporins down a water potential gradient
Verified step by step guidance1
Step 1: Understand the difference between passive and active transport. Passive transport does not require energy and moves substances down their concentration gradient, while active transport requires energy to move substances against their concentration gradient.
Step 2: Identify the examples given: simple diffusion of O2, facilitated diffusion of glucose, osmosis of water, and Na+ uptake via the Na+/K+ ATPase pump.
Step 3: Recognize that simple diffusion, facilitated diffusion, and osmosis all move substances down their concentration or water potential gradients and do not require energy input, so they are forms of passive transport.
Step 4: Understand that the Na+/K+ ATPase pump uses ATP to actively transport Na+ ions against their concentration gradient, which classifies it as primary active transport.
Step 5: Conclude that the Na+ uptake driven by the Na+/K+ ATPase is the form of active transmembrane transport because it requires energy input to move ions against their gradient.
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