Multiple Choice
Facilitated diffusion moves substances across a membrane via specific transport proteins. Is facilitated diffusion an active or passive transport process?
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9. Transport Across Membranes
Passive Transport: Diffusion and Osmosis
Multiple Choice
In the context of passive transport across cell membranes, what is the key difference between simple diffusion and facilitated diffusion?
A
Facilitated diffusion occurs only in prokaryotic cells, whereas simple diffusion occurs only in eukaryotic cells.
B
Facilitated diffusion requires specific membrane transport proteins (channels or carriers) to move substances down their concentration gradient, whereas simple diffusion occurs directly through the lipid bilayer without proteins.
C
Facilitated diffusion moves substances against their concentration gradient using ATP, whereas simple diffusion moves substances down their concentration gradient without ATP.
D
Facilitated diffusion can only transport water molecules, whereas simple diffusion can only transport ions.
Verified step by step guidance1
Identify the main concept: passive transport across cell membranes involves movement of substances without energy input (ATP).
Understand simple diffusion: substances move directly through the lipid bilayer from an area of higher concentration to an area of lower concentration without the help of proteins.
Understand facilitated diffusion: substances move down their concentration gradient but require specific membrane transport proteins (such as channels or carriers) to assist their passage across the membrane.
Compare the two: the key difference lies in the involvement of membrane proteins—simple diffusion does not require proteins, while facilitated diffusion does.
Note that both processes move substances down their concentration gradient and do not require energy (ATP), distinguishing them from active transport.
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