Which is not present in prokaryotes :-

Options

A. plasma membrane
B. nuclear membrane
C. cell wall
D. ribosome

Answer

To determine which structure is not present in prokaryotes, we need to analyze the options provided: plasma membrane, nuclear membrane, cell wall, and mesosome.

### Step-by-Step Solution:

1. **Understanding Prokaryotic Cells**:
- Prokaryotic cells are simple, unicellular organisms that lack membrane-bound organelles. They do not have a well-defined nucleus.

2. **Analyzing the Options**:
- **Plasma Membrane**: This is present in all cells, including prokaryotes. It serves as a barrier that regulates what enters and exits the cell.
- **Nuclear Membrane**: Prokaryotes do not have a true nucleus; instead, their genetic material is located in a region called the nucleoid. Since there is no nucleus, there cannot be a nuclear membrane.
- **Cell Wall**: Most prokaryotes have a cell wall that provides structure and protection. It is made of peptidoglycan in bacteria.
- **Mesosome**: This is an infolding of the plasma membrane in prokaryotes and is involved in various functions, including cell division and respiration.

3. **Conclusion**:
- Since prokaryotes lack a well-defined nucleus, they also lack a nuclear membrane. Therefore, the correct answer to the question is the **nuclear membrane**.

### Final Answer:
The structure that is not present in prokaryotes is the **nuclear membrane**.

---