Which of the following statements about the plasma membrane is TRUE ?

Options

A. It allows selected molecules to pass into and out of the cell .
B. It is a rigid and unmoving layer of phospholipids and protein .
C. It is a solid layer of protein that protects the contents of the cell.
D. The plasma membrane of a bacterium has none of the same components as the plasma membrane of an animal cell.

Answer

To determine which statement about the plasma membrane is true, we need to analyze each option provided.

### Step-by-Step Solution:

1. **Understanding the Plasma Membrane**: The plasma membrane is a biological membrane that separates and protects the interior of all cells from the outside environment. It is composed mainly of a phospholipid bilayer with embedded proteins.

2. **Evaluating Statement 1**: The first statement claims that the plasma membrane allows selected molecules to pass from inside to outside. This is true because the plasma membrane is selectively permeable, meaning it regulates the movement of substances in and out of the cell. It allows certain ions and molecules to pass while restricting others.

3. **Evaluating Statement 2**: The second statement suggests that the plasma membrane is rigid. This is false; the plasma membrane is not rigid but rather fluid in nature. It exhibits fluidity due to the movement of phospholipids and proteins within the bilayer.

4. **Evaluating Statement 3**: The third statement claims that the plasma membrane is a solid layer that protects the cell contents. This is also incorrect. While the plasma membrane does provide some protection, its primary role is in transport and signaling, not as a solid protective barrier.

5. **Evaluating Statement 4**: The fourth statement asserts that the plasma membrane of bacteria does not contain the same components as that of animal cells. This is misleading. While there are differences in the composition of bacterial and animal cell membranes, both types of membranes share fundamental components such as phospholipids and proteins. Therefore, this statement is also false.

6. **Conclusion**: After evaluating all the statements, we find that only Statement 1 is true. The plasma membrane allows selected molecules to pass from inside to outside, confirming its role as a selectively permeable barrier.

### Final Answer:
**Statement 1 is TRUE.**

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