Which of the following is not true concerning the plasma membrane?

Options

A. It is responsible for maintaining an electrochemical gradient between the inside and outside of the cell
B. It is composed of folds known as cristae
C. It is composed of phospholipids and proteins
D. It helps protect the internal contents of the cell

Explanation

To determine which statement about the plasma membrane is not true, we will evaluate each option provided in the question.

### Step-by-Step Solution:

1. **Evaluate the First Statement**:
- The first statement claims that the plasma membrane is responsible for maintaining the electrochemical gradient between the inside and outside of the cell.
- **Analysis**: This is true. The plasma membrane plays a crucial role in maintaining the electrochemical gradient, which is essential for various cellular functions.

2. **Evaluate the Second Statement**:
- The second statement suggests that the plasma membrane is composed of folds known as cristae.
- **Analysis**: This is false. Cristae are actually folds found in the inner membrane of mitochondria, not in the plasma membrane. The plasma membrane is primarily composed of a lipid bilayer and does not have cristae.

3. **Evaluate the Third Statement**:
- The third statement indicates that the plasma membrane is composed of phospholipids and proteins.
- **Analysis**: This is true. The plasma membrane is indeed made up of a phospholipid bilayer with embedded proteins, which is a fundamental aspect of its structure.

4. **Evaluate the Fourth Statement**:
- The fourth statement asserts that the plasma membrane protects the internal components of the cell.
- **Analysis**: This is also true. The plasma membrane serves as a barrier that protects the internal environment of the cell from the external environment.

### Conclusion:
Based on the evaluations, the statement that is not true concerning the plasma membrane is that it is composed of folds known as cristae.

### Final Answer:
**The statement that is not true concerning the plasma membrane is: "It is composed of folds known as cristae."**

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