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

Question

In a biological system, the diffusion of a lipophilic substance across a cell membrane is primarily limited by:

B VENKAT · Accepted Answer

## CORE INFORMATION
✓ **Answer**: B
## CONCEPT FRAMEWORK
 **Primary Concept**: Membrane transport of lipophilic substances
 **Related Topics**: Cell membrane structure, diffusion, Fick's law
 **Prerequisites**: Understanding of cell membrane composition (lipid bilayer, aqueous compartments), principles of diffusion.
## SOLUTION PATHWAY
**Given Information**:
  The substance is lipophilic (fat-soluble).
  The question asks about the primary limiting factor for its diffusion across a cell membrane.
**Method & Steps**:
 1. Consider the properties of a lipophilic substance and the cell membrane.
  Reasoning: Lipophilic substances can readily dissolve in the hydrophobic core of the lipid bilayer.  Therefore, the rate of diffusion through this core is relatively fast.
 2. Analyze the different factors influencing diffusion across the membrane.
  Working:  
            * **Hydrophobic core:** Lipophilic substances easily traverse this. 
            * **Aqueous unstirred layers:** These are layers of stagnant water adjacent to the membrane on both sides.  The substance must dissolve in this aqueous phase before reaching the membrane's lipid core, and this process can be slow, especially for lipophilic molecules which are poorly soluble in water.
            * **Membrane proteins:**  While membrane proteins facilitate the transport of many substances, lipophilic substances generally don't require protein channels or carriers for their passage across the membrane.
            * **Concentration gradient:** The concentration gradient is the driving force for diffusion, but it doesn't dictate the *rate-limiting step*.  A steep gradient simply means the diffusion will be *faster*, but the *limiting factor* remains the same.
 3. Identify the primary limiting factor.
  Result: The aqueous unstirred layers are the primary limiting factor because the substance must dissolve in these layers before it can diffuse through the lipid bilayer.
  Verification:  The speed of diffusion through the lipid bilayer is generally much faster than the rate of dissolution in and diffusion through the unstirred layers.
 ## OPTION ANALYSIS
A :x: The hydrophobic core is readily permeable to lipophilic substances; it's not the limiting factor.
B ✓: The aqueous unstirred layers represent a significant barrier to diffusion, especially for lipophilic substances due to their low solubility in water.
C :x: Membrane proteins are not primarily involved in the diffusion of lipophilic substances.
D :x: The concentration gradient is a driving force, but the rate-limiting step is the passage through the aqueous unstirred layers.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Assuming that the lipid bilayer is the major barrier:  Lipophilic molecules pass this layer relatively easily.
  2.Overlooking the role of aqueous unstirred layers: These layers are often ignored but are crucial in determining the overall rate of diffusion.
 **Quick Tips**:
  1.Remember that 'lipophilic' means 'fat-loving' and therefore readily soluble in lipids but not in water.
  2.Visualize the cell membrane with the unstirred layers as additional layers of resistance to diffusion.

B VENKAT · Answer

The hydrophobic core of the lipid bilayer

B VENKAT · Answer

The correct Option is "The aqueous unstirred layers adjacent to the membrane"

B VENKAT · Answer

The presence of membrane proteins

B VENKAT · Answer

The concentration gradient of the substance

NEET Botany Transport in Plants Diffusion MCQs

Select Topic

Question Tags

NEET Subjects

Our Bots

Company