Multiple Choice
Which of the following sets correctly lists three major types of active transmembrane transport used by cells?
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9. Transport Across Membranes
Principles of Transmembrane Transport
Multiple Choice
In the context of principles of transmembrane transport, when would a cell have to use active transport to move a solute across the plasma membrane?
A
When moving water across the membrane by osmosis through aquaporins.
B
When moving a solute from higher concentration to lower concentration through a simple diffusion pathway.
C
When moving a solute down its electrochemical gradient through an ion channel (facilitated diffusion).
D
When moving a solute from lower concentration to higher concentration (against its electrochemical gradient).
Verified step by step guidance1
Step 1: Understand the difference between passive and active transport. Passive transport moves solutes down their concentration or electrochemical gradients without energy input, while active transport requires energy to move solutes against these gradients.
Step 2: Recognize that osmosis through aquaporins is a passive process where water moves from an area of lower solute concentration to higher solute concentration, following its concentration gradient, so no energy is needed.
Step 3: Identify that simple diffusion and facilitated diffusion (through ion channels) both move solutes down their concentration or electrochemical gradients, which also do not require energy.
Step 4: Note that active transport is necessary when a cell moves a solute from a region of lower concentration to higher concentration, i.e., against its concentration or electrochemical gradient, which requires energy input (usually ATP).
Step 5: Conclude that the cell must use active transport specifically when moving solutes against their electrochemical gradients, as this process cannot occur spontaneously and requires energy.
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