The Question is from neet-botany plant-physiology , and it was created by the author K SURESH KUMAR

Question

Which type of molecule is LEAST likely to cross a cell membrane by simple diffusion?

K SURESH KUMAR · Accepted Answer

## CORE INFORMATION
✓ **Answer**: C
## CONCEPT FRAMEWORK
 **Primary Concept**: Cell membrane permeability and simple diffusion
 **Related Topics**: Hydrophobicity, polarity, molecular size, membrane transport
 **Prerequisites**: Understanding of cell membrane structure (phospholipid bilayer), properties of polar and nonpolar molecules.
## SOLUTION PATHWAY
**Given Information**:
  The question asks about the molecule LEAST likely to cross a cell membrane by simple diffusion.
  Simple diffusion is the passive movement of molecules across a membrane from an area of high concentration to an area of low concentration.
**Method & Steps**:
 1. Consider the properties of the cell membrane:
  Reasoning: The cell membrane is primarily composed of a phospholipid bilayer, which has a hydrophobic (water-fearing) core and hydrophilic (water-loving) heads.  Small, nonpolar molecules can easily pass through this hydrophobic core because they are not repelled by it.
  Formula/Rule: None directly applicable; this is a conceptual understanding problem.
 2. Analyze the effect of molecule size and polarity:
  Working: Larger molecules have a harder time squeezing through the membrane's tight spaces. Polar molecules are repelled by the hydrophobic core and require assistance to cross (e.g., facilitated diffusion or active transport).
  Key Point: The combination of large size and polarity creates the greatest barrier to simple diffusion.
 3. Determine the least likely molecule to cross by simple diffusion:
  Result: A large, polar molecule is least likely to cross by simple diffusion due to its size and its interaction with the hydrophobic core of the membrane. 
  Verification: The other options represent molecules that can more easily pass through the membrane by simple diffusion.
 ## OPTION ANALYSIS
A :x: Small, nonpolar molecules readily diffuse across the membrane.
B :x: Small, polar molecules can diffuse, but less easily than nonpolar molecules.
C ✓: Large, polar molecules are too large and too polar to easily diffuse across the hydrophobic core of the membrane.
D :x: Small, uncharged molecules are generally able to diffuse across the membrane.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Overlooking the importance of both size and polarity: Students might focus only on one factor and incorrectly choose a smaller or less polar molecule as the least likely to diffuse.
  2.Confusing simple diffusion with other transport methods: Simple diffusion does not require energy or transporter proteins. 
 **Quick Tips**:
  1.Remember “like dissolves like”: Nonpolar molecules pass easily through the nonpolar core of the membrane.
  2.Visualize the cell membrane: Imagine the hydrophobic core as a barrier that repels polar molecules.

K SURESH KUMAR · Answer

Small, nonpolar molecule

K SURESH KUMAR · Answer

Small, polar molecule

K SURESH KUMAR · Answer

The correct Option is "Large, polar molecule"

K SURESH KUMAR · Answer

Small, uncharged molecule

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