According to unit membrane concept the plasma membrane has the following arrangement

Options

A. protein and lipid layers intermingled
B. protein-lipid-protein
C. lipid-protein-lipid
D. protein-lipid-lipid

Answer

### Step-by-Step Solution

1. **Understanding the Unit Membrane Concept**: The unit membrane concept was proposed by Robertson in 1935. It describes the structure of biological membranes, particularly animal cell membranes.

2. **Structure of the Plasma Membrane**: According to this concept, the plasma membrane consists of a lipid bilayer that is flanked by protein layers on both sides. This arrangement resembles a sandwich, where the lipid layer is the filling and the proteins are the bread.

3. **Components of the Membrane**:
- **Lipid Layer**: The central part of the membrane is composed of lipids, which are hydrophobic in nature.
- **Protein Layers**: Surrounding the lipid bilayer are protein layers that are hydrophilic, meaning they interact well with water.

4. **Arrangement of Layers**: The correct arrangement of the plasma membrane according to the unit membrane concept is:
- **Protein** (outer layer) - **Lipid** (middle layer) - **Protein** (inner layer).
This is often abbreviated as PLP (Protein-Lipid-Protein).

5. **Evaluating the Options**: The question provides several options:
- Protein and lipid layers intermingled
- Protein-Lipid-Protein
- Lipid-Protein-Lipid
- Protein-Lipid-Lipid
The correct answer is **Protein-Lipid-Protein**.

6. **Conclusion**: The plasma membrane, according to the unit membrane concept, has a structure that consists of a lipid bilayer sandwiched between two protein layers.