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Certain integral membrane proteins facilitate the diffusion of molecules across the membrane without directly binding to the transported molecule. These proteins create a continuous aqueous pathway through the lipid bilayer. Which of the following is the BEST example of such facilitated diffusion?
GLUT transporters moving glucose
Sodium-potassium pump maintaining ion gradients
Aquaporins transporting water
Chloride channels gated by voltage
A researcher is studying facilitated diffusion of a novel solute 'X' across a cell membrane using an artificial lipid bilayer system. They observe that increasing the concentration of X on one side of the membrane increases the rate of transport, but only up to a certain point. Beyond this point, further increases in X concentration do not affect the transport rate. Which of the following BEST explains this observation?
The membrane has reached its maximum permeability for X.
The solute X is being actively transported at higher concentrations.
Saturation of the carrier proteins
The solute X is inhibiting its own transport through feedback regulation.
Which characteristic distinguishes facilitated diffusion from simple diffusion across a biological membrane?
Movement down a concentration gradient
Specificity for the transported molecule
Passive transport requiring no energy input
Dependence on membrane fluidity
A mutation in an aquaporin gene results in a non-functional protein. Which of the following cellular processes would be MOST directly affected?
Glucose uptake by muscle cells
Sodium transport across nerve cell membranes
Water reabsorption in the kidneys
Calcium storage in the sarcoplasmic reticulum
In a hypothetical cell, the facilitated diffusion of a solute 'Y' is observed to be significantly faster than predicted by simple diffusion models. However, the transport rate plateaus at high concentrations of Y. Which of the following is the MOST likely explanation for this observation?
The cell membrane is selectively permeable to Y.
The solute Y is transported via carrier proteins.
The solute Y is undergoing active transport.
The cell is modifying Y during transport.
Which of the following statements regarding facilitated diffusion is INCORRECT?
It requires transport proteins.
It is a passive process and does not require energy.
It can move molecules against their concentration gradient.
Transport proteins involved can become saturated.
In facilitated diffusion, molecules move across the membrane with the help of:
ATP hydrolysis
Membrane proteins
Concentration gradient against their movement
Vesicle formation
Facilitated diffusion differs from simple diffusion in that:
Facilitated diffusion requires membrane proteins, while simple diffusion does not.
Facilitated diffusion moves substances against their concentration gradient, while simple diffusion moves them down their concentration gradient.
Facilitated diffusion requires energy expenditure, while simple diffusion does not.
Facilitated diffusion occurs only in plant cells, while simple diffusion occurs in all cells.
Which of the following is NOT a characteristic of facilitated diffusion?
It requires specific membrane proteins.
It does not require ATP.
It is a passive process.
It moves substances against their concentration gradient.
The transport of glucose into most animal cells occurs via:
Simple diffusion
Facilitated diffusion using channel proteins
Facilitated diffusion using carrier proteins
Active transport
