Which of these cell organelles found exclusively in eukaryotes is not membrane bound?

Options

A. Ribosomes
B. Cilia
C. Nucleolus
D. Lysosome

Answer

To solve the question, "Which of these cell organelles found exclusively in eukaryotes is not membrane-bound?" we will analyze each option provided.

### Step-by-Step Solution:

1. **Understanding the Question**: We need to identify a cell organelle that is found only in eukaryotic cells and is not surrounded by a membrane.

2. **Analyzing the Options**:
- **Option 1: Ribosome**:
- Ribosomes are responsible for protein synthesis and are composed of RNA and proteins.
- They are not membrane-bound organelles.
- However, ribosomes are found in both prokaryotic and eukaryotic cells, so this option does not satisfy the criteria of being exclusive to eukaryotes.

- **Option 2: Cilia**:
- Cilia are hair-like structures that extend from the surface of some eukaryotic cells and are involved in movement and sensory functions.
- They are extensions of the cell membrane and are not considered organelles in the traditional sense.
- Thus, they do not fit the criteria of being an organelle that is exclusive to eukaryotes.

- **Option 3: Nucleolus**:
- The nucleolus is a spherical structure found within the nucleus of eukaryotic cells.
- It is involved in the synthesis of ribosomal RNA and is not surrounded by a membrane.
- The nucleolus is indeed exclusive to eukaryotic cells, making this a strong candidate.

- **Option 4: Lysosome**:
- Lysosomes are membrane-bound organelles that contain digestive enzymes.
- Since they are surrounded by a membrane, this option does not meet the criteria.

3. **Conclusion**: After analyzing all the options, the only organelle that is found exclusively in eukaryotes and is not membrane-bound is the **nucleolus**.

### Final Answer:
The correct answer is **Nucleolus**.

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