What is the thickness of plasma membrane ?

Explanation

**Step-by-Step Solution:**

1. **Understanding Plasma Membrane**: The plasma membrane is the outermost covering of a cell. It serves as a barrier between the cell's interior and the external environment.

2. **Function of Plasma Membrane**: It is known as a selectively permeable membrane, meaning it allows certain molecules to enter or exit the cell while restricting others. This selectivity is crucial for maintaining the cell's internal environment.

3. **Structure of Plasma Membrane**: The plasma membrane is primarily composed of a phospholipid bilayer. This means it consists of two layers of phospholipid molecules arranged in such a way that their hydrophilic (water-attracting) heads face outward towards the water inside and outside the cell, while their hydrophobic (water-repelling) tails face inward, away from water.

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