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.
Related Questions
Facilitated diffusion differs from simple diffusion in that it:
Requires ATP
Moves substances against their concentration gradient
Requires membrane proteins
Occurs only in plant cells
    Read the following statements regarding porins and select the correct option given below
I.    Porins are transport proteins
II.    Channel proteins are a type of transport protein, which are usually gated
III.    Carrier protein binds the particular solute to be transported
IV.    Particular solute is delivered to the other side of the membrane by carrier proteins
I, II and III
I, III and IV
I, II, III and IV
I and IV
Facilitated diffusion is different from simple diffusion because it:
Moves molecules against the concentration gradient
Uses carrier proteins
Requires ATP
Occurs only in plant cells
Which statement can be shared by facilitated diffusion and active transport?
    Both need carrier transporter, which are sensitive to inhibitors that reacts with protein side chains
    Energy is required by both the processes
    No energy expenditure in these processes
Both use carbohydrates to move molecules
across the membrane
Facilitated diffusion does not require/show
Special membrane proteins
Saturation of transport
ATP energy
Selective nature
Which statement can be shared by facilitated diffusion and active transport?
    Both need carrier transporter, which are sensitive to inhibitors that reacts with protein side chains
    Energy is required by both the processes
    No energy expenditure in these processes
Both use carbohydrates to move molecules
across the membrane
    Select the wrong statement regarding membrane channels
    They are proteins
They are usually gated, i.e., may be open or closed
    All ions pass through the same type of channel
    They form a huge pore in the outer membrane of plastids, mitochondria and some bacteria
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.
In facilitated diffusion, saturation occurs when:
The concentration gradient disappears.
All carrier proteins are occupied by the transported substance.
The cell runs out of ATP.
The temperature decreases significantly.
Active transport differs from facilitated transport as the former
Requires special membrane protein
Is highly selective
Shows response to protein inhibitors
Is ATP dependent
