Multiple Choice
In the context of membrane transporters, which statement best describes facilitated diffusion?
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9. Transport Across Membranes
Transporters
Multiple Choice
In most mammalian cells, how does glucose typically enter the cell across the plasma membrane under normal physiological conditions?
A
By vesicular uptake through clathrin-mediated endocytosis as the main mechanism
B
By facilitated diffusion through GLUT transporters down its concentration gradient
C
By simple diffusion through the lipid bilayer because glucose is nonpolar
D
By primary active transport via the /-ATPase directly pumping glucose into the cytosol
Verified step by step guidance1
Step 1: Understand the nature of glucose and the plasma membrane. Glucose is a polar molecule, which means it cannot easily pass through the hydrophobic lipid bilayer of the plasma membrane by simple diffusion.
Step 2: Recognize that glucose transport into mammalian cells typically requires a specific transport mechanism because of its polarity and size.
Step 3: Identify the main transport method: facilitated diffusion, which uses specific carrier proteins called GLUT transporters. These transporters allow glucose to move down its concentration gradient without the use of cellular energy (ATP).
Step 4: Differentiate facilitated diffusion from other mechanisms such as active transport (which requires energy) and endocytosis (which involves vesicle formation). Glucose uptake in most mammalian cells does not primarily occur via these methods under normal physiological conditions.
Step 5: Conclude that glucose enters mammalian cells mainly by facilitated diffusion through GLUT transporters, moving from higher extracellular glucose concentration to lower intracellular concentration.
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