Which of these is a unicellular organism ?

Options

A. Paramecium
B. Spider
C. Mosquito
D. Seaweed

Answer

To determine which of the given options is a unicellular organism, we will analyze each option one by one.

### Step-by-Step Solution:

1. **Identify the Options**: We have four options to consider:
- Option A: Paramecium
- Option B: Spider
- Option C: Mosquito
- Option D: Seaweed

2. **Analyze Option A (Paramecium)**:
- Paramecium is a well-known unicellular organism. It is a type of protist that consists of a single cell and performs all necessary life functions within that one cell.
- **Conclusion**: Paramecium is unicellular.

3. **Analyze Option B (Spider)**:
- Spiders are classified as arachnids, which are multicellular organisms. They have complex body structures made up of multiple cells.
- **Conclusion**: Spider is multicellular.

4. **Analyze Option C (Mosquito)**:
- Mosquitoes are insects and are also multicellular organisms. They have specialized cells and tissues that perform various functions.
- **Conclusion**: Mosquito is multicellular.

5. **Analyze Option D (Seaweed)**:
- Seaweed is a type of macroalgae and is also multicellular. It consists of many cells organized into tissues.
- **Conclusion**: Seaweed is multicellular.

6. **Final Conclusion**:
- After analyzing all the options, the only unicellular organism among the given choices is **Option A: Paramecium**.

### Final Answer:
The unicellular organism from the options provided is **Paramecium**.