All single cell organisms are known as prokaryotes. The single cell performs all the functions required for the organism to survive.
Which of the following cell organelles is not present in prokaryotes?

Options

A. Nucleus
B. Cell wall
C. Ribosome
D. Cell membrane

Answer

To determine which cell organelle is not present in prokaryotes, we will analyze the options provided one by one.

### Step-by-Step Solution:

1. **Understanding Prokaryotes**: Prokaryotes are single-celled organisms that lack a well-defined nucleus and membrane-bound organelles. They include bacteria and archaea.

2. **Analyzing the Options**:
- **Option 1: Nucleus**: Prokaryotic cells do not have a true nucleus. Instead, their genetic material is located in a region called the nucleoid. Therefore, this option is correct; prokaryotes do not have a nucleus.
- **Option 2: Cell Wall**: Most prokaryotes have a cell wall that provides structure and protection. Hence, this option is incorrect; prokaryotes do have a cell wall.
- **Option 3: Ribosomes**: Prokaryotes contain ribosomes, which are essential for protein synthesis. Therefore, this option is also incorrect; prokaryotes do have ribosomes.
- **Option 4: Cell Membrane**: Prokaryotes have a cell membrane that controls the movement of substances in and out of the cell. Thus, this option is incorrect; prokaryotes do have a cell membrane.

3. **Conclusion**: Based on the analysis, the organelle that is not present in prokaryotes is the **nucleus**.

### Final Answer:
The cell organelle that is not present in prokaryotes is the **nucleus**.