Multiple Choice
In the context of principles of transmembrane transport, what does it mean that the cell membrane is selectively permeable?
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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 distinguishes facilitated diffusion from active transport?
A
Facilitated diffusion requires ATP hydrolysis, whereas active transport never uses cellular energy.
B
Facilitated diffusion moves solutes down their electrochemical gradient without direct energy input, whereas active transport moves solutes against their electrochemical gradient using an energy source (e.g., ATP hydrolysis or ion gradients).
C
Facilitated diffusion is always non-saturable, whereas active transport is never saturable.
D
Facilitated diffusion can only occur through lipid bilayers without proteins, whereas active transport always occurs through channels.
Verified step by step guidance1
Step 1: Understand the basic definitions of facilitated diffusion and active transport. Facilitated diffusion is a passive transport process where molecules move across a membrane through specific transport proteins without the use of cellular energy, moving down their electrochemical gradient.
Step 2: Recognize that active transport requires energy input (such as ATP hydrolysis or energy from ion gradients) to move solutes against their electrochemical gradient, which is from lower to higher concentration or against electrical charge differences.
Step 3: Identify that facilitated diffusion does not require ATP or direct energy because it relies on the natural movement of molecules down their gradient, whereas active transport uses energy to move molecules against this gradient.
Step 4: Note that both facilitated diffusion and active transport involve proteins in the membrane, but facilitated diffusion uses carrier proteins or channels to allow passive movement, while active transport uses pumps that consume energy.
Step 5: Conclude that the correct distinguishing statement is: Facilitated diffusion moves solutes down their electrochemical gradient without direct energy input, whereas active transport moves solutes against their electrochemical gradient using an energy source (e.g., ATP hydrolysis or ion gradients).
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