According to the fluid mosaic model of membrane structure, proteins of the membrane are :

Options

A. spread in a continuous layer over the inner and outer surfaces of the membrane
B. confined to the hydrophobic core of the membrane
C. randomly oriented in the membrane, with no fixed inside-outside polarity
D. embedded in a lipid bilayer

Explanation

**Step-by-Step Solution:**

1. **Understanding the Fluid Mosaic Model**: The fluid mosaic model describes the structure of cell membranes. It emphasizes that the membrane is not a rigid structure but rather a fluid combination of lipids and proteins.

2. **Identifying the Components of the Membrane**: The membrane consists of a phospholipid bilayer, where the hydrophilic (water-loving) heads face outward and the hydrophobic (water-fearing) tails face inward. Proteins are interspersed within this bilayer.

3. **Analyzing the Options**:
- **Option 1**: "Spread in continuous layer over the inner and outer surface of the membrane." This is incorrect because the proteins are not in a continuous layer; they are distributed randomly.
- **Option 2**: "Confined to the hydrophobic core of the membrane." This is also incorrect. While some proteins may interact with the hydrophobic core, many are located on the outer and inner surfaces of the membrane.
- **Option 3**: "Randomly oriented in the membrane with no fixed polarity." This is partially incorrect. While proteins are randomly oriented, they do have a fixed polarity based on their hydrophobic and hydrophilic regions.
- **Option 4**: "Embedded in the lipid bilayer." This is correct. Many proteins are indeed embedded within the lipid bilayer, either spanning the membrane (integral proteins) or associated with one side (peripheral proteins).

4. **Conclusion**: Based on the analysis, the correct statement according to the fluid mosaic model is that proteins are embedded in the lipid bilayer.

**Final Answer**: Proteins of the membrane are embedded in the lipid bilayer.

---