Give the main difference between the Danielli and Davson model and Robertson model of molecular structure of cell membrane.

Explanation

### Step-by-Step Solution:

1. **Introduction to the Models**:
- The Danielli and Davson model (1935) is known as the Sandwich model, while the Robertson model (1959) is referred to as the Unit membrane model.
- Both models describe the structure of the cell membrane but differ in their specifics.

2. **Basic Structure**:
- Both models propose a phospholipid bilayer as the fundamental structure of the cell membrane.
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