Cilia & flagella are absent in life cycle of :-

Options

A. Red algae
B. Brown algae
C. Green algae
D. Red algae & B.G.A

Answer

To solve the question "Cilia & flagella are absent in life cycle of:", we will analyze the characteristics of the given options: red algae, brown algae, green algae, and blue-green algae.

### Step-by-Step Solution:

1. **Understanding Cilia and Flagella**:
- Cilia and flagella are structures used for movement in many organisms. They are hair-like projections that can help in locomotion or moving fluids.

2. **Analyzing Red Algae**:
- Red algae (Rhodophyta) are known to have a eukaryotic cell structure. Importantly, they do not possess flagella at any stage of their life cycle. They also contain phycobiliproteins and have unstacked thylakoids in their chloroplasts.

3. **Analyzing Brown Algae**:
- Brown algae (Phaeophyta) typically have flagellated reproductive cells. For example, their sperm cells are flagellated, which means they do have cilia or flagella at certain stages of their life cycle.

4. **Analyzing Green Algae**:
- Green algae (Chlorophyta) also possess flagellated cells, especially in their reproductive stages, where sperm cells are usually motile due to flagella.

5. **Analyzing Blue-Green Algae**:
- Blue-green algae (Cyanobacteria) are prokaryotic and do not have cilia or flagella. However, they can exhibit gliding movement due to slime secretion, but they lack true flagella.

6. **Conclusion**:
- Based on the analysis, both red algae and blue-green algae do not have cilia and flagella in their life cycles. However, since the question asks for the absence of cilia and flagella in the life cycle, the most appropriate answer is **red algae**.

### Final Answer:
Cilia and flagella are absent in the life cycle of **red algae**.

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