Multiple Choice
In the context of principles of transmembrane transport, why does active transport require an input of energy (e.g., ATP hydrolysis or an ion gradient)?
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9. Transport Across Membranes
Principles of Transmembrane Transport
Multiple Choice
Which of the following is an active transport process across the plasma membrane?
A
Simple diffusion of O2 directly through the lipid bilayer
B
Facilitated diffusion of glucose through a GLUT transporter down its concentration gradient
C
Osmosis of water through aquaporins down its water potential gradient
D
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 it requires energy and moves substances against their concentration gradient. Simple diffusion, facilitated diffusion, and osmosis all move substances down their gradients and do not require energy.
Step 3: Recognize that the Na+/K+ ATPase uses ATP hydrolysis to pump Na+ out and K+ into the cell, moving ions against their concentration gradients, which classifies it as active transport.
Step 4: Recall that active transport processes often involve specific transport proteins or pumps that use energy to move molecules or ions against their gradients.
Step 5: Conclude that among the given options, only the Na+/K+ ATPase represents an active transport mechanism because it requires ATP and moves ions against their concentration gradients.
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