Blue colour of blue -green algae is due to

Options

A. Phycocyanin and allophycocyanin
B. Phycoerythrin
C. Anthocyanin
D. Anthoxanthin.

Answer

### Step-by-Step Solution:

1. **Identify the Organism**: The question asks about the blue color of blue-green algae. Blue-green algae are also known as cyanobacteria.

2. **Understand the Pigments**: The color of algae is determined by the pigments they contain. Different pigments absorb and reflect different wavelengths of light, which gives the algae their characteristic colors.

3. **Analyze the Options**:
- **Option 1: Phycocyanin and Allophycocyanin**: These are blue pigments found in blue-green algae. The term "cyanin" indicates a blue color, and these pigments contain copper, which contributes to the blue appearance.
- **Option 2: Phycoerythrin**: This pigment is responsible for red color and is found in red algae, not blue-green algae.
- **Option 3: Anthocyanin**: These pigments are red to purplish and are typically found in fruits and vegetables, not in blue-green algae.
- **Option 4: Anthoxanthin**: These are pale yellow or white pigments found in plants like onions and cauliflower, and are not related to blue-green algae.

4. **Conclusion**: Based on the analysis, the blue color of blue-green algae is primarily due to the presence of phycocyanin and allophycocyanin. Therefore, the correct answer is Option 1.

### Final Answer:
The blue color of blue-green algae is due to **phycocyanin and allophycocyanin**.

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