Multiple Choice
In the context of principles of transmembrane transport, active transport across a membrane requires which of the following?
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9. Transport Across Membranes
Principles of Transmembrane Transport
Multiple Choice
In the context of principles of transmembrane transport, what best defines secondary active transport?
A
Transport of a solute against its concentration gradient by coupling it to the downhill movement of another ion or solute whose gradient was previously established by primary active transport (e.g., symport or antiport).
B
Net movement of molecules down their concentration gradient through a membrane channel or carrier without any energy input.
C
Direct transport of a solute against its concentration gradient using energy from ATP hydrolysis by the transporter itself (e.g., P-type ATPases).
D
Vesicle-mediated movement of macromolecules across the plasma membrane via endocytosis or exocytosis.
Verified step by step guidance1
Step 1: Understand the concept of transmembrane transport, which involves moving substances across a cell membrane either with or against their concentration gradients.
Step 2: Recognize that primary active transport uses direct energy input (like ATP hydrolysis) to move solutes against their concentration gradient, establishing an ion gradient.
Step 3: Define secondary active transport as the process where the movement of one solute against its concentration gradient is coupled to the movement of another solute down its previously established gradient, which was created by primary active transport.
Step 4: Identify that secondary active transport can occur via symport (both solutes move in the same direction) or antiport (solutes move in opposite directions) mechanisms.
Step 5: Differentiate secondary active transport from passive transport (no energy input, solutes move down their gradient) and vesicle-mediated transport (bulk movement of macromolecules), focusing on the coupling of uphill and downhill solute movements.
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