Blue - green algae can be upto

Options

A. `10mu m` long
B. `50mu m` long
C. `25mu m` long
D. 0.5- 1 mu m long

Answer

### Step-by-Step Solution

1. **Understand Blue-Green Algae**: Blue-green algae are also known as cyanobacteria. They are photosynthetic organisms that contain both blue and green pigments.

2. **Identify the Characteristics**: Blue-green algae are prokaryotic in nature, meaning they lack a defined nucleus and other membrane-bound organelles. They are also known for their role in nitrogen fixation.

3. **Determine the Size**: The question asks about the size of blue-green algae. The options provided are:
- Option 1: 10 µm
- Option 2: 50 µm
- Option 3: 25 µm
- Option 4: 0.5 to 1 µm

4. **Analyze the Options**:
- Blue-green algae can vary in size, but they are generally much smaller than the other options listed.
- The correct size range for blue-green algae is typically between 0.5 to 1 µm.

5. **Select the Correct Answer**: Based on the analysis, the correct answer is **Option 4: 0.5 to 1 µm**. The other options (10 µm, 50 µm, and 25 µm) are too large for blue-green algae.

### Final Answer
The size of blue-green algae can be up to **0.5 to 1 µm**.

---