Multiple Choice
In the context of principles of transmembrane transport, what are the two main types of active transport across cell membranes?
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9. Transport Across Membranes
Principles of Transmembrane Transport
Multiple Choice
In the context of transmembrane transport, which statement best distinguishes passive transport from active transport?
A
Passive transport occurs only for water via aquaporins, whereas active transport occurs only for ions via channels.
B
Passive transport increases concentration differences across the membrane, whereas active transport eliminates concentration differences until equilibrium is reached.
C
Passive transport moves substances down their electrochemical gradient without direct energy input, whereas active transport moves substances against their electrochemical gradient using an energy source (e.g., ATP hydrolysis or an ion gradient).
D
Passive transport always requires a specific membrane pump protein, whereas active transport occurs only by simple diffusion through the lipid bilayer.
Verified step by step guidance1
Step 1: Understand the definitions of passive and active transport in the context of transmembrane movement of substances. Passive transport involves movement of molecules without the use of cellular energy, while active transport requires energy input.
Step 2: Recognize that passive transport moves substances down their electrochemical gradient, meaning from an area of higher concentration or electrical potential to an area of lower concentration or electrical potential, without the need for ATP or other energy sources.
Step 3: Understand that active transport moves substances against their electrochemical gradient, from lower to higher concentration or electrical potential, which requires an energy source such as ATP hydrolysis or coupling to another ion gradient.
Step 4: Evaluate the given statements by comparing them to these definitions. Identify which statement correctly captures the key difference: energy use and direction relative to the electrochemical gradient.
Step 5: Conclude that the correct distinguishing statement is the one that says passive transport moves substances down their electrochemical gradient without direct energy input, whereas active transport moves substances against their electrochemical gradient using an energy source.
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