Plasma membrane is fluid structure due to presence of :–

Options

A. Carbohydrate
B. Lipid
C. Glycoprotein
D. Polysaccharide

Answer

**Step-by-Step Solution:**

1. **Understanding the Plasma Membrane**: The plasma membrane, also known as the cell membrane, is the outer boundary of all cells, except for plant cells which have a cell wall in addition to the plasma membrane.

2. **Composition of the Plasma Membrane**: The plasma membrane is primarily composed of a phospholipid bilayer. This bilayer consists of two layers of phospholipids, which are molecules that have hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails.

3. **Role of Lipids in Fluidity**: The fluid nature of the plasma membrane is largely due to the presence of lipids. The lipids can be either saturated or unsaturated. Unsaturated lipids have one or more double bonds in their fatty acid chains, which creates kinks that prevent the lipids from packing closely together.

4. **Effect of Unsaturation on Fluidity**: The more unsaturated the lipids in the membrane, the greater the fluidity. This is because unsaturated lipids create more space between the molecules, allowing them to move more freely.

5. **Evaluating the Options**:
- Option 1: Cholesterol - While cholesterol does play a role in maintaining membrane integrity and fluidity, it is not the primary reason for the fluid structure.
- Option 2: Lipid - This is the correct answer as lipids are the main component that contributes to the fluid nature of the membrane.
- Option 3: Glycoprotein - Glycoproteins are involved in cell recognition and signaling but do not contribute to the fluidity of the membrane.
- Option 4: Polysaccharide - Similar to glycoproteins, polysaccharides are involved in cell structure and recognition but do not affect fluidity.

6. **Conclusion**: The correct answer is that the plasma membrane is a fluid structure due to the presence of lipids.

**Final Answer**: Lipid (Option 2)

---