Cell membrane contains

Options

A. Alternate layers of phospholipid and coline
B. Double layers of phospholipid
C. Double layers of phospholipid with polar ends projected outside
D. Double layers of phospholipid with polar ends projected inside

Answer

### Step-by-Step Solution:

1. **Understanding the Structure of the Cell Membrane**:
The cell membrane, also known as the plasma membrane, is primarily composed of a double layer of phospholipids. Each phospholipid molecule has a hydrophilic (water-attracting) "head" and two hydrophobic (water-repelling) "tails".

2. **Phospholipid Bilayer Formation**:
In an aqueous environment, phospholipids arrange themselves into a bilayer. The hydrophilic heads face outward towards the water inside and outside the cell, while the hydrophobic tails face inward, away from the water.

3. **Orientation of the Phospholipids**:
As a result of this arrangement, the cell membrane has two layers of phospholipids. The outer layer is exposed to the external environment, while the inner layer is exposed to the cytoplasm of the cell.

4. **Additional Components of the Cell Membrane**:
Besides phospholipids, the cell membrane also contains proteins, cholesterol, and carbohydrates. Proteins can be integral (spanning the membrane) or peripheral (attached to the surface). Cholesterol helps to maintain fluidity, and carbohydrates are involved in cell recognition and signaling.

5. **Conclusion**:
Therefore, the cell membrane contains a double layer of phospholipids with the polar heads projected outward (toward the aqueous environment) and the hydrophobic tails projected inward (away from the aqueous environment).

### Final Answer:
The cell membrane contains a double layer of phospholipids with polar heads projected outward and hydrophobic tails projected inward.

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