Multiple Choice
In the context of principles of transmembrane transport, which type of cell transport requires an input of energy (e.g., ATP or an ion gradient) to move substances across a membrane?
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9. Transport Across Membranes
Principles of Transmembrane Transport
Multiple Choice
Which of the following is the best definition of active transport across a biological membrane?
A
Movement of solutes across a membrane against their electrochemical gradient using energy (directly from ATP hydrolysis or indirectly from coupling to another gradient).
B
Movement of solutes down their electrochemical gradient through a membrane protein without direct energy input (facilitated diffusion).
C
Movement of water across a semipermeable membrane driven by differences in solute concentration (osmosis).
D
Movement of solutes down their concentration gradient through a membrane without any protein involvement.
Verified step by step guidance1
Step 1: Understand the concept of active transport in cell biology. Active transport refers to the movement of molecules or ions across a biological membrane against their electrochemical gradient, which requires energy input.
Step 2: Recognize that energy for active transport can come directly from ATP hydrolysis or indirectly from coupling the transport to another gradient (such as an ion gradient). This distinguishes active transport from passive processes.
Step 3: Compare active transport to other types of membrane transport: facilitated diffusion (movement down gradient via proteins without energy), osmosis (water movement driven by solute concentration differences), and simple diffusion (movement down concentration gradient without proteins).
Step 4: Identify that the key feature of active transport is movement against the electrochemical gradient with energy expenditure, which is not true for facilitated diffusion, osmosis, or simple diffusion.
Step 5: Conclude that the best definition of active transport is: 'Movement of solutes across a membrane against their electrochemical gradient using energy (directly from ATP hydrolysis or indirectly from coupling to another gradient)'.
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