Multiple Choice
In the context of principles of transmembrane transport, which process does NOT require direct energy input from the cell (e.g., ATP hydrolysis)?
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9. Transport Across Membranes
Principles of Transmembrane Transport
Multiple Choice
In the context of principles of transmembrane transport, which statement best distinguishes passive transport from active transport across a biological membrane?
A
Passive transport requires ATP hydrolysis, whereas active transport never requires cellular energy.
B
Passive transport moves substances down their electrochemical gradient without direct energy input, whereas active transport moves substances against their electrochemical gradient using energy (e.g., ATP hydrolysis or coupling to another gradient).
C
Passive transport can move solutes against their electrochemical gradient if the concentration difference is small, whereas active transport cannot.
D
Passive transport always requires a membrane protein pump, whereas active transport occurs only by simple diffusion through the lipid bilayer.
Verified step by step guidance1
Understand the basic definitions: Passive transport is the movement of substances across a membrane without the use of cellular energy, while active transport requires energy input to move substances.
Recognize the role of electrochemical gradients: Passive transport moves substances down their electrochemical gradient (from high to low concentration or electrical potential), whereas active transport moves substances against this gradient (from low to high concentration or electrical potential).
Identify the energy source: Active transport uses energy, often from ATP hydrolysis or coupling to another gradient, to move substances against their gradient; passive transport does not use direct energy.
Consider the mechanisms involved: Passive transport can occur via simple diffusion or facilitated diffusion through membrane proteins, but it never requires energy; active transport involves membrane proteins that function as pumps requiring energy.
Summarize the key distinction: The best distinguishing statement is that passive transport moves substances down their electrochemical gradient without direct energy input, while active transport moves substances against their electrochemical gradient using energy.
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