Multiple Choice
Which statement best defines active transport across a biological 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 best distinguishes active transport from passive transport?
A
Active transport is always faster than passive transport because it does not require a membrane protein.
B
Active transport occurs only through channels, whereas passive transport occurs only through pumps (ATPases).
C
Active transport requires an energy input (e.g., ATP or an ion gradient) to move solutes against their electrochemical gradient, whereas passive transport moves solutes down their electrochemical gradient without direct energy input.
D
Active transport moves solutes down their electrochemical gradient without energy input, whereas passive transport requires ATP hydrolysis to move solutes against the gradient.
Verified step by step guidance1
Step 1: Understand the definitions of passive and active transport. Passive transport moves solutes down their electrochemical gradient without requiring energy, while active transport moves solutes against their electrochemical gradient and requires energy input.
Step 2: Recognize that passive transport can occur through channels or carrier proteins and does not use ATP or other energy sources directly.
Step 3: Identify that active transport requires energy, often from ATP hydrolysis or an existing ion gradient, to move molecules against their concentration or electrochemical gradient.
Step 4: Note that active transport involves specific proteins such as pumps (e.g., ATPases) that use energy to transport solutes, whereas passive transport relies on facilitated diffusion or simple diffusion.
Step 5: Conclude that the key distinguishing feature is the energy requirement and direction relative to the electrochemical gradient: active transport requires energy to move solutes against the gradient, passive transport does not require energy and moves solutes down the gradient.
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