Lipid bilayers in biomembranes are barrier to

Options

A. polar molecules
B. non polar molecules
C. both polar and non polar molecules
D. none

Answer

### Step-by-Step Solution:

1. **Understanding the Structure of Lipid Bilayers**:
- Lipid bilayers are composed of two layers of phospholipids. Each phospholipid molecule has a hydrophilic (water-attracting) "head" and two hydrophobic (water-repelling) "tails".

2. **Function of Lipid Bilayers**:
- The lipid bilayer acts as a semi-permeable membrane, meaning it allows certain substances to pass through while restricting others.

3. **Identifying What Cannot Pass Through**:
- The lipid bilayer is primarily a barrier to polar molecules. This is because polar molecules, which are hydrophilic, cannot easily pass through the hydrophobic (water-repelling) interior of the bilayer.

4. **Examples of Polar and Non-Polar Molecules**:
- Polar molecules include ions, sugars, and proteins, which cannot easily diffuse through the lipid bilayer.
- Non-polar molecules, such as oxygen and carbon dioxide, can diffuse freely through the lipid bilayer due to their hydrophobic nature.

5. **Conclusion**:
- Based on the properties of the lipid bilayer, it acts as a barrier primarily to polar molecules. Therefore, the correct answer to the question is that lipid bilayers in biomembranes are barriers to **polar molecules**.

### Final Answer:
- Lipid bilayers in biomembranes are barriers to **polar molecules**.