Multiple Choice
In the context of transmembrane transport, which statement best distinguishes passive transport from active transport?
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9. Transport Across Membranes
Principles of Transmembrane Transport
Multiple Choice
In the context of transmembrane transport, which statement best describes how passive transport differs from active transport?
A
Passive transport moves solutes against their electrochemical gradient, whereas active transport moves solutes down their electrochemical gradient.
B
Passive transport moves solutes down their electrochemical gradient without direct energy input, whereas active transport moves solutes against their electrochemical gradient using an energy source (e.g., ATP hydrolysis or an ion gradient).
C
Passive transport always requires ATP, whereas active transport never requires cellular energy input.
D
Passive transport can occur only through protein pumps, whereas active transport occurs only by simple diffusion through the lipid bilayer.
Verified step by step guidance1
Step 1: Understand the concept of electrochemical gradient, which combines both the concentration gradient and the electrical potential difference across the membrane. Solutes tend to move from areas of high to low electrochemical potential naturally.
Step 2: Define passive transport as the movement of solutes down their electrochemical gradient without the need for direct energy input from the cell. This process can occur via simple diffusion or facilitated diffusion through channel or carrier proteins.
Step 3: Define active transport as the movement of solutes against their electrochemical gradient, which requires an input of energy. This energy often comes from ATP hydrolysis or from coupling to another ion gradient (secondary active transport).
Step 4: Compare the two processes by noting that passive transport relies on the natural tendency of molecules to move down gradients, while active transport works against this tendency and thus requires energy.
Step 5: Use this understanding to evaluate the given statements and identify the one that correctly describes the difference between passive and active transport based on energy use and direction relative to the electrochemical gradient.
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