The cell membrane is composed of lipids that are arranged in

Answer

### Step-by-Step Solution:

1. **Understanding the Composition of the Cell Membrane**: The cell membrane is primarily composed of lipids and proteins. The main type of lipid found in the cell membrane is phospholipids.

2. **Identifying the Arrangement of Lipids**: The lipids in the cell membrane are arranged in a specific structure. This arrangement is crucial for the functionality of the membrane.

3. **Introducing the Fluid Mosaic Model**: The arrangement of lipids and proteins in the cell membrane is explained by the Fluid Mosaic Model, which was proposed by Singer and Nicolson in the 1970s.

4. **Describing the Bilayer Structure**: According to the Fluid Mosaic Model, the lipids are arranged in a bilayer. This means that there are two layers of lipids. The hydrophilic (water-attracting) heads of the phospholipids face outward towards the aqueous environment, while the hydrophobic (water-repelling) tails face inward, away from water.

5. **Summarizing the Arrangement**: Therefore, the correct answer to the question is that the cell membrane is composed of lipids that are arranged in a **bilayer**.

### Final Answer:
The cell membrane is composed of lipids that are arranged in a **bilayer**.

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