A scientist observes a drop of pond water under an electron microscope. He sees a microorganism with no specific cell structure. Which of these can it be?

Options

A. Virus
B. Fungi
C. Algae
D. Protozoa

Answer

To solve the question about the microorganism observed under an electron microscope, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Microorganisms**: Microorganisms are tiny living organisms that cannot be seen with the naked eye and require a microscope for observation. They include various types such as bacteria, viruses, fungi, algae, and protozoa.

2. **Identifying the Characteristics**: The question specifies that the microorganism has "no specific cell structure." This means it lacks the typical components found in cells, such as a nucleus, organelles, a cell membrane, and cytoplasm.

3. **Analyzing the Options**:
- **Virus**: Viruses are unique in that they do not have a complete cell structure. They consist of a protein coat and genetic material (DNA or RNA) but lack cellular components like a nucleus or organelles.
- **Fungi**: Fungi have a defined cell structure, including a cell wall, nucleus, and organelles.
- **Algae**: Algae are also cellular organisms with a defined structure, including chloroplasts and a cell wall.
- **Protozoa**: Protozoa are single-celled organisms that have a complex cell structure, including a nucleus and organelles.

4. **Eliminating Options**: Since the microorganism observed has no specific cell structure, we can eliminate fungi, algae, and protozoa from consideration.

5. **Conclusion**: The only option that fits the description of having no specific cell structure is a virus. Therefore, the correct answer is **Virus**.

### Final Answer:
The microorganism observed by the scientist is a **Virus**.