The giant algae or sea weeds belong to class.

Options

A. Xanthophyceae
B. Phaeophyceae
C. Rhodophyceae
D. Chlorophyceae.

Answer

**Step-by-Step Text Solution:**

1. **Understanding Algae Classification**: Algae are classified into three major classes based on their color and the pigments they contain. The three classes are:
- Chlorophyceae (Green Algae)
- Phaeophyceae (Brown Algae)
- Rhodophyceae (Red Algae)

2. **Identifying the Pigments**:
- **Chlorophyceae**: Contains chlorophyll A and B.
- **Phaeophyceae**: Contains chlorophyll A and C, along with xanthophylls, particularly fucoxanthin, which gives them a brownish color.
- **Rhodophyceae**: Contains chlorophyll A and D, along with phycoerythrin, which gives them a red color.

3. **Determining the Class of Giant Algae**: The question specifically asks about giant algae or seaweeds. The largest forms of algae, commonly referred to as seaweeds, fall under the category of brown algae (Phaeophyceae).

4. **Examples of Giant Algae**: The giant algae, also known as kelps, include species like:
- **Macrocystis**: Can grow up to 40 to 100 meters.
- **Neurocystis**: Can reach lengths of approximately 20 to 30 meters.

5. **Conclusion**: Since giant algae or seaweeds are classified as brown algae, the correct answer to the question is **Phaeophyceae**.

**Final Answer**: The giant algae or seaweeds belong to the class **Phaeophyceae**.

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