Multiple Choice
In the context of transmembrane transport, what is the main difference between simple diffusion and facilitated diffusion across a lipid bilayer?
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9. Transport Across Membranes
Principles of Transmembrane Transport
Multiple Choice
In the context of principles of transmembrane transport, active transport across a membrane requires which of the following?
A
Only a phospholipid bilayer, because transporters are not involved in active transport
B
Movement of solutes down their concentration gradient through an open channel without energy input
C
Equal solute concentrations on both sides of the membrane so that net flux is zero
D
An input of energy (e.g., ATP hydrolysis or coupling to an ion gradient) to move solutes against their electrochemical gradient
Verified step by step guidance1
Understand the difference between passive and active transport: Passive transport moves solutes down their concentration or electrochemical gradient without energy input, while active transport moves solutes against their gradient and requires energy.
Recognize that a phospholipid bilayer alone does not facilitate active transport; specific transporter proteins are necessary to move solutes across the membrane.
Recall that movement of solutes down their concentration gradient through open channels is characteristic of passive transport, not active transport.
Note that equal solute concentrations on both sides of the membrane result in no net flux, which is unrelated to the energy requirement of active transport.
Conclude that active transport requires an input of energy, such as ATP hydrolysis or coupling to an ion gradient, to move solutes against their electrochemical gradient.
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