Multiple Choice
In passive transport, how does most commonly cross the cell membrane?
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9. Transport Across Membranes
Passive Transport: Diffusion and Osmosis
Multiple Choice
In the context of passive transport across a cell membrane, what is the key difference between simple diffusion and facilitated diffusion?
A
Simple diffusion can only move water across membranes, whereas facilitated diffusion can only move ions.
B
Facilitated diffusion moves molecules against their concentration gradient, whereas simple diffusion moves molecules down their concentration gradient.
C
Simple diffusion uses ATP to pump molecules across the membrane, whereas facilitated diffusion does not require ATP.
D
Facilitated diffusion requires specific membrane proteins (channels or carriers) to move substances down their concentration gradient, whereas simple diffusion occurs directly through the lipid bilayer without transport proteins.
Verified step by step guidance1
Understand that both simple diffusion and facilitated diffusion are types of passive transport, meaning they move substances across the cell membrane without using cellular energy (ATP).
Recognize that simple diffusion involves the direct movement of small or nonpolar molecules (like oxygen or carbon dioxide) through the lipid bilayer of the membrane, without the assistance of any proteins.
Identify that facilitated diffusion requires specific membrane proteins, such as channel proteins or carrier proteins, to help move molecules that cannot easily cross the lipid bilayer on their own (like glucose or ions).
Note that both processes move substances down their concentration gradient, from an area of higher concentration to an area of lower concentration, and neither requires energy input.
Summarize the key difference: simple diffusion occurs directly through the membrane lipids, while facilitated diffusion depends on membrane proteins to transport molecules across the membrane.
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