Multiple Choice
In the context of principles of transmembrane transport, what does active transport require to move a solute across a membrane against its electrochemical gradient?
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9. Transport Across Membranes
Principles of Transmembrane Transport
Multiple Choice
In the context of principles of transmembrane transport, which statement correctly describes the difference between simple diffusion and facilitated diffusion across a cell membrane?
A
Simple diffusion requires ATP hydrolysis, whereas facilitated diffusion does not require ATP.
B
Simple diffusion is saturable at high solute concentrations, whereas facilitated diffusion is never saturable.
C
Simple diffusion moves solutes against their concentration gradient, whereas facilitated diffusion moves solutes down their concentration gradient.
D
Simple diffusion occurs directly through the lipid bilayer without a transport protein, whereas facilitated diffusion requires a membrane transport protein (channel or carrier) but still moves solute down its concentration gradient.
Verified step by step guidance1
Step 1: Understand the basic concept of simple diffusion. Simple diffusion is the movement of molecules directly through the lipid bilayer of the cell membrane without the assistance of any proteins, driven solely by the concentration gradient (from high to low concentration).
Step 2: Understand facilitated diffusion. Facilitated diffusion also moves molecules down their concentration gradient, but it requires specific membrane transport proteins, such as channels or carriers, to help solutes cross the membrane because these solutes cannot easily pass through the lipid bilayer on their own.
Step 3: Compare energy requirements. Both simple diffusion and facilitated diffusion are passive processes, meaning neither requires ATP hydrolysis or energy input; they rely on the natural movement of molecules down their concentration gradients.
Step 4: Consider saturation and specificity. Simple diffusion is not saturable because it does not involve proteins, whereas facilitated diffusion can be saturable because the transport proteins have a limited number of binding sites and can become fully occupied at high solute concentrations.
Step 5: Summarize the key difference. The main distinction is that simple diffusion occurs directly through the lipid bilayer without transport proteins, while facilitated diffusion requires specific membrane proteins to assist solute movement, but both processes move solutes down their concentration gradients without using energy.
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