Plasma membrane is asymmetric because

Options

A. Lipids present in the outer and inner side of the bilayer are different.
B. Extrinsic proteins are more abundant on the inner surface than on the outer surface.
C. Oligosaccharides are attached only to the external surface of lipids and proteins of a biomembrane
D. All of these

Answer

### Step-by-Step Solution:

1. **Understanding the Plasma Membrane Structure**: The plasma membrane, also known as the cell membrane, is a bilayer composed of lipids and proteins. It separates the interior of the cell from the external environment.

2. **Asymmetry of the Plasma Membrane**: The plasma membrane is described as asymmetric because the composition of its outer and inner layers is not the same. This asymmetry is crucial for various cellular functions.

3. **Role of Oligosaccharides**: On the outer surface of the plasma membrane, there are carbohydrate molecules known as oligosaccharides. These oligosaccharides consist of 8 to 10 monosaccharide units.

4. **Functions of Oligosaccharides**:
- **Cell to Cell Adhesion**: Oligosaccharides play a significant role in helping cells stick to each other.
- **Cell Recognition**: They are involved in the recognition processes between cells, which is critical for immune response and tissue formation.
- **Cell Communication**: Oligosaccharides also facilitate communication between cells, allowing them to respond to external signals.

5. **Conclusion on Asymmetry**: The presence of oligosaccharides only on the external surface of the plasma membrane contributes to its asymmetry. This is why the plasma membrane is asymmetric.

6. **Final Answer**: The plasma membrane is asymmetric because oligosaccharides are attached only to the external surface of lipids and proteins of the biomembrane.