The lipid bilayer of cell membrane is impermeable to:

Options

A. large uncharged polar molecules
B. small uncharged polar molecules
C. hydrophobic molecules
D. hydrophilic molecules

Explanation

To determine which substances the lipid bilayer of a cell membrane is impermeable to, we need to analyze the properties of different types of molecules in relation to the cell membrane structure.

### Step-by-Step Solution:

1. **Understanding the Cell Membrane Structure**:
- The cell membrane is primarily composed of a lipid bilayer, which consists of phospholipids. This structure is hydrophobic (water-repelling) in nature, meaning it does not allow certain substances to pass through easily.

**Hint**: Remember that the lipid bilayer's hydrophobic nature plays a crucial role in determining permeability.

2. **Identifying Types of Molecules**:
- Molecules can be categorized based on their size and polarity:
- **Large Uncharged Polar Molecules**: Examples include glucose and amino acids.
- **Small Uncharged Polar Molecules**: Examples include water, oxygen, and carbon dioxide.
- **Hydrophobic Molecules**: Non-polar molecules like oils and fats.
- **Hydrophilic Molecules**: Polar molecules that can form hydrogen bonds with water, such as sugars.

**Hint**: Classify the molecules based on their size and charge to understand their permeability.

3. **Analyzing Permeability**:
- **Large Uncharged Polar Molecules**: These molecules are too large to pass through the lipid bilayer easily. They cannot diffuse through the membrane.
- **Small Uncharged Polar Molecules**: These can pass through the membrane due to their small size.
- **Hydrophobic Molecules**: These can also pass through the membrane as they are non-polar.
- **Hydrophilic Molecules**: While they are polar, their ability to pass through depends on their size; smaller hydrophilic molecules can sometimes pass through, but larger ones cannot.

**Hint**: Focus on the size and charge of the molecules when considering their ability to cross the membrane.

4. **Conclusion**:
- Based on the analysis, the lipid bilayer of the cell membrane is impermeable to **large uncharged polar molecules**. This is because their size and polarity prevent them from diffusing through the hydrophobic core of the membrane.

**Final Answer**: The lipid bilayer of the cell membrane is impermeable to **large uncharged polar molecules**.