The basic structure of the cell membrane

Options

A. is a lipid bilayer that serves as a barries to water - soluble molecules.
B. is a lipid bilayer that serves as a barries to lipid - soluble molecules.
C. is best described as lipids dispersed within a protein bilayer.
D. is a protein bilayer that serves as a barrier to lipid- soluble molecules.

Answer

### Step-by-Step Solution:

1. **Understanding Cell Membrane Structure**: The cell membrane, also known as the plasma membrane, is primarily composed of a double layer of phospholipids, which is referred to as the lipid bilayer.

2. **Phospholipid Arrangement**: In the lipid bilayer, phospholipids are arranged in such a way that their hydrophilic (water-attracting) phosphate heads face outward towards the aqueous environment, while their hydrophobic (water-repelling) fatty acid tails face inward, away from water.

3. **Function of the Lipid Bilayer**: The lipid bilayer serves as a barrier to water-soluble molecules. This means that substances that are soluble in water cannot easily pass through the membrane, while lipid-soluble molecules can pass through more freely.

4. **Evaluating Options**:
- **Option A**: "A lipid bilayer that serves as a barrier to water-soluble molecules" - This is correct because the lipid bilayer indeed acts as a barrier to water-soluble substances.
- **Option B**: "A lipid bilayer that serves as a barrier to lipid-soluble molecules" - This is incorrect because lipid-soluble molecules can pass through the lipid bilayer.
- **Option C**: "Lipids disperse within a protein bilayer" - This is incorrect as the bilayer is primarily made of lipids, not proteins.
- **Option D**: "A protein bilayer that serves as a barrier to lipid-soluble molecules" - This is also incorrect because the main structure is a lipid bilayer, not a protein bilayer.

5. **Conclusion**: The correct description of the basic structure of the cell membrane is "a lipid bilayer that serves as a barrier to water-soluble molecules."