Multiple Choice
Which of the following is an example of active transport across a cell membrane?
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9. Transport Across Membranes
Principles of Transmembrane Transport
Multiple Choice
In the context of principles of transmembrane transport, which statement correctly contrasts facilitated diffusion with active transport?
A
Facilitated diffusion requires ATP hydrolysis to move solutes down their electrochemical gradient, whereas active transport does not require energy input.
B
Facilitated diffusion can occur only through the lipid bilayer without proteins, whereas active transport always occurs through protein channels.
C
Facilitated diffusion moves solutes down their electrochemical gradient via specific transport proteins without direct energy input, whereas active transport moves solutes against their electrochemical gradient using energy (e.g., ATP hydrolysis or coupling to another gradient).
D
Facilitated diffusion moves solutes against their electrochemical gradient using pumps, whereas active transport moves solutes down their electrochemical gradient through open channels.
Verified step by step guidance1
Step 1: Understand the basic definitions of facilitated diffusion and active transport. Facilitated diffusion is a passive transport process where solutes move down their electrochemical gradient through specific transport proteins without using cellular energy.
Step 2: Recognize that active transport requires energy input (such as ATP hydrolysis) to move solutes against their electrochemical gradient, often using protein pumps or transporters.
Step 3: Identify that facilitated diffusion does not require ATP or other energy sources because it relies on the natural movement of molecules from high to low concentration or electrochemical potential.
Step 4: Note that facilitated diffusion involves transport proteins (like channels or carriers), but it does not occur directly through the lipid bilayer without proteins, which contradicts one of the incorrect statements.
Step 5: Summarize the correct contrast: facilitated diffusion moves solutes down their electrochemical gradient via specific transport proteins without direct energy input, whereas active transport moves solutes against their electrochemical gradient using energy (e.g., ATP hydrolysis or coupling to another gradient).
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