What did Nicolson and Singer propose?

Explanation

**Step-by-Step Solution:**

1. **Introduction to the Proposal**: In 1972, scientists S.J. Singer and Garth L. Nicolson proposed a significant model regarding the structure of biological membranes.

2. **Name of the Model**: The model they proposed is known as the **Fluid Mosaic Model**.

3. **Description of the Model**:
- The Fluid Mosaic Model describes the cell membrane as a **lipid bilayer**. This bilayer consists of two layers of phospholipids.
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