Multiple Choice
In the context of transmembrane transport, what is the key difference between simple diffusion and facilitated diffusion across a biological membrane?
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9. Transport Across Membranes
Principles of Transmembrane Transport
Multiple Choice
Active transport is different from simple diffusion because active transport:
A
always occurs directly through the lipid bilayer without the involvement of transport proteins
B
moves solutes only down their concentration gradient without requiring any energy input
C
can move solutes against their concentration or electrochemical gradient by using an energy source (e.g., ATP or an ion gradient)
D
is driven exclusively by random thermal motion of molecules and requires no membrane proteins
Verified step by step guidance1
Step 1: Understand the key difference between active transport and simple diffusion. Simple diffusion is a passive process where molecules move from an area of higher concentration to an area of lower concentration without energy input.
Step 2: Recognize that active transport requires energy to move solutes against their concentration or electrochemical gradient, which is opposite to the direction of passive diffusion.
Step 3: Identify that active transport involves specific transport proteins embedded in the membrane, such as pumps, which use energy sources like ATP or ion gradients to move molecules.
Step 4: Note that simple diffusion does not require transport proteins and is driven by random thermal motion, whereas active transport is a regulated process requiring energy and proteins.
Step 5: Conclude that the correct distinguishing feature of active transport is its ability to move solutes against their gradient using energy, unlike simple diffusion which moves solutes down their gradient without energy.
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