The basic structure of the cell membrane

Options

A. is a lipid bilayer that serves as a barries to water - soluble molecules.
B. is a lipid bilayer that serves as a barries to lipid - soluble molecules.
C. is best described as lipids dispersed within a protein bilayer.
D. is a protein bilayer that serves as a barrier to lipid- soluble molecules.

Answer

To understand the basic structure of the cell membrane, we can break it down into several key points:

### Step-by-Step Solution:

1. **Definition of Cell Membrane**: The cell membrane, also known as the plasma membrane, is a biological membrane that separates and protects the interior of all cells from the outside environment.

2. **Lipid Bilayer Structure**: The fundamental structure of the cell membrane is the lipid bilayer. This bilayer consists of two layers of lipid molecules, primarily phospholipids. Each phospholipid has a hydrophilic (water-attracting) "head" and two hydrophobic (water-repelling) "tails."

3. **Barrier Function**: The lipid bilayer serves as a barrier to water-soluble molecules. This means that substances that are soluble in water cannot easily pass through the membrane without assistance. The hydrophobic tails of the phospholipids prevent water-soluble substances from crossing the membrane freely.

4. **Protein Integration**: Embedded within this lipid bilayer are proteins that can either span the membrane (integral proteins) or be attached to its surface (peripheral proteins). These proteins play crucial roles in transport, signaling, and maintaining the structure of the membrane.

5. **Fluid Mosaic Model**: The cell membrane is often described by the fluid mosaic model, which depicts the membrane as a dynamic and flexible structure where lipids and proteins can move laterally within the layer, contributing to the membrane's functionality.

6. **Conclusion**: The correct statement regarding the basic structure of the cell membrane is that it is a lipid bilayer that serves as a barrier to water-soluble molecules.

### Final Answer:
The correct answer is: **A lipid bilayer that serves as the barrier to water-soluble molecules.**

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