The Question is from neet-botany plant-physiology , and it was created by the author B VENKAT

Question

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?

B VENKAT · Accepted Answer

## CORE INFORMATION
✓ **Answer**: C
## CONCEPT FRAMEWORK
 **Primary Concept**: Facilitated Diffusion and Carrier Protein Saturation
 **Related Topics**: Membrane transport, kinetics of enzyme reactions
 **Prerequisites**: Understanding of facilitated diffusion, the role of carrier proteins in membrane transport.
## SOLUTION PATHWAY
**Given Information**:
  * Facilitated diffusion of solute X across an artificial lipid bilayer.
  * Increasing concentration of X increases transport rate initially.
  * Beyond a certain point, increasing X concentration does not further increase transport rate.
**Method & Steps**:
 1. Analyze the observation: The initial increase in transport rate with increasing X concentration indicates that the transport is facilitated by a carrier protein.  The plateauing of the transport rate at higher X concentrations suggests that the carrier proteins are saturated.
  Reasoning:  Facilitated diffusion utilizes carrier proteins to move solutes across the membrane. These proteins have a limited number of binding sites for the solute. 
  Formula/Rule:  None directly applicable, but the concept is analogous to enzyme kinetics where a reaction rate plateaus at saturation.
 2. Eliminate incorrect options: Options A, B, and D don't explain the plateauing effect.
  Working:  Option A is incorrect because permeability refers to the ease with which a substance can cross a membrane, not the number of carrier proteins available.
  Option B is incorrect because the question specifies facilitated diffusion, a passive process; active transport requires energy.
  Option D is incorrect because there is no evidence of feedback regulation in the problem description.
 3. Conclude: The only explanation that fits the observation is the saturation of carrier proteins. Once all binding sites are occupied, further increases in X concentration cannot increase the transport rate.
  Result: Saturation of carrier proteins (Option C)
  Verification: The explanation aligns perfectly with the observed behavior in facilitated diffusion.
 ## OPTION ANALYSIS
A :x: The membrane permeability is not the limiting factor; the number of available carrier proteins is.
B :x: The description points to passive transport (facilitated diffusion), not active transport.
C ✓: This correctly explains the plateauing of the transport rate due to the limited number of carrier proteins.
D :x: There is no mention of feedback regulation in the problem description. 
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing facilitated diffusion with active transport: Remember that facilitated diffusion does not require energy input.
  2.Misinterpreting the plateau as a change in membrane permeability: The plateau is due to saturation of carrier proteins, not a change in membrane properties.
 **Quick Tips**:
  1.Think of the analogy with enzyme kinetics and substrate saturation.
  2.Remember that facilitated diffusion uses carrier proteins with limited binding sites.

B VENKAT · Answer

The membrane has reached its maximum permeability for X.

B VENKAT · Answer

The solute X is being actively transported at higher concentrations.

B VENKAT · Answer

The correct Option is "Saturation of the carrier proteins"

B VENKAT · Answer

The solute X is inhibiting its own transport through feedback regulation.

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