Multiple Choice
Transporters always require energy to move solutes across a membrane?
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9. Transport Across Membranes
Transporters
Multiple Choice
In the context of membrane transporters, which statement best describes facilitated diffusion?
A
It moves solutes up their concentration gradient and always requires ATP hydrolysis by an ATPase transporter.
B
It requires a specific membrane transporter that selectively binds the solute and moves it down its concentration gradient without ATP hydrolysis.
C
It is a vesicular transport process in which solutes enter the cell by endocytosis mediated by clathrin.
D
It allows any small polar molecule to cross the lipid bilayer directly without a transporter because the process is passive.
Verified step by step guidance1
Step 1: Understand the concept of facilitated diffusion in membrane transport. Facilitated diffusion is a passive transport mechanism that allows specific molecules to cross the cell membrane with the help of membrane proteins, without the use of cellular energy (ATP).
Step 2: Recognize that facilitated diffusion moves solutes down their concentration gradient, meaning from an area of higher concentration to an area of lower concentration, which does not require energy input.
Step 3: Identify that facilitated diffusion requires specific membrane transporters, such as channel proteins or carrier proteins, which selectively bind to the solute to assist its passage across the lipid bilayer.
Step 4: Differentiate facilitated diffusion from active transport, which moves solutes against their concentration gradient and requires ATP hydrolysis, and from vesicular transport processes like endocytosis, which involve membrane invagination and vesicle formation.
Step 5: Conclude that facilitated diffusion does not allow any small polar molecule to cross the membrane directly without a transporter; instead, it requires specific transport proteins to enable selective and efficient transport.
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