Multiple Choice
During osmosis, water moves primarily in response to a difference in which of the following across a selectively permeable membrane?
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9. Transport Across Membranes
Passive Transport: Diffusion and Osmosis
Multiple Choice
In the context of passive transport across the plasma membrane, how do simple diffusion and facilitated diffusion differ?
A
Simple diffusion can transport ions efficiently across the membrane, whereas facilitated diffusion cannot transport ions.
B
Simple diffusion requires ATP hydrolysis, whereas facilitated diffusion does not require energy input.
C
Facilitated diffusion requires specific membrane proteins (channels or carriers), whereas simple diffusion occurs directly through the lipid bilayer without transport proteins.
D
Facilitated diffusion moves solutes against their concentration gradient, whereas simple diffusion moves solutes down their concentration gradient.
Verified step by step guidance1
Step 1: Understand the concept of passive transport, which is the movement of molecules across the plasma membrane without the input of cellular energy (ATP). Both simple diffusion and facilitated diffusion fall under this category.
Step 2: Define simple diffusion as the process where small, nonpolar molecules move directly through the lipid bilayer of the plasma membrane, moving down their concentration gradient without the assistance of membrane proteins.
Step 3: Define facilitated diffusion as the process where molecules that cannot easily cross the lipid bilayer (such as polar or charged molecules) move down their concentration gradient with the help of specific membrane proteins, such as channel proteins or carrier proteins.
Step 4: Highlight the key difference: simple diffusion does not require transport proteins and occurs directly through the membrane, whereas facilitated diffusion requires specific membrane proteins to assist the movement of molecules.
Step 5: Clarify that both simple and facilitated diffusion move solutes down their concentration gradient and do not require energy input, distinguishing them from active transport mechanisms.
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