Multiple Choice
In the context of transmembrane transport, which statement best distinguishes active transport from facilitated diffusion?
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9. Transport Across Membranes
Principles of Transmembrane Transport
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)?
A
Because it moves solutes down their electrochemical gradient, which always requires ATP to proceed.
B
Because it moves solutes against their electrochemical gradient, which is thermodynamically unfavorable without energy input.
C
Because it eliminates membrane selectivity by forming nonspecific pores that require ATP to remain open.
D
Because it allows solutes to diffuse directly through the lipid bilayer without any transport protein.
Verified step by step guidance1
Step 1: Understand the concept of electrochemical gradients, which combine both concentration gradients and electrical charge differences across a membrane, influencing the movement of solutes.
Step 2: Recognize that passive transport moves solutes down their electrochemical gradient, which is thermodynamically favorable and does not require energy input.
Step 3: Identify that active transport moves solutes against their electrochemical gradient, meaning from lower to higher concentration or against the electrical potential, which is thermodynamically unfavorable.
Step 4: Realize that because moving solutes against their gradient requires work, cells must provide energy, often through ATP hydrolysis or by coupling to another ion gradient, to drive this process.
Step 5: Conclude that active transport requires energy input to overcome the thermodynamic barrier of moving solutes against their electrochemical gradient, ensuring selective and regulated transport across membranes.
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