Which of the following is correct regarding the structure of a section of cilia / flagella ?

Options

A. `{:("Peripheral","Central","Radial","Central"),("Microtubules","mictotubules","spokes","sheath"),("(doublets)","(singlets)",,),(" "9+0," 2"," 8"," 1"):}`
B. `{:("Peripheral","Central","Radial","Central"),("Microtubules","mictotubules","spokes","sheath"),("(doublets)","(singlets)",,),(" "9+2," 9+0"," 9"," 1"):}`
C. `{:("Peripheral","Central","Radial","Central"),("Microtubules","mictotubules","spokes","sheath"),("(doublets)","(singlets)",,),(" "9," 2"," 9"," 1"):}`
D. `{:("Peripheral","Central","Radial","Central"),("Microtubules","mictotubules","spokes","sheath"),("(doublets)","(singlets)",,),(" "3," 6"," 9"," 1"):}`

Explanation

To determine the correct structure of cilia and flagella, we need to analyze the options provided based on the known organization of microtubules in these structures. Here’s a step-by-step breakdown of the solution:

### Step-by-Step Solution:

1. **Understanding Cilia and Flagella**:
- Cilia and flagella are hair-like structures that extend from the surface of cells and are involved in cell movement.
- Cilia are shorter and more numerous, while flagella are longer and typically fewer in number.

2. **Structure of Cilia and Flagella**:
- Both structures are cylindrical and arise from basal bodies (similar to centrioles).
- The core of cilia and flagella is called the axoneme.

3. **Microtubule Arrangement**:
- The axoneme consists of microtubules arranged in a specific pattern.
- The typical arrangement is known as the "9 + 2" structure, which means:
- There are **9 peripheral microtubule doublets** arranged in a circle around the outside.
- There are **2 central microtubules** in the center.

4. **Radial Spokes and Central Sheath**:
- Each peripheral doublet is connected to the central sheath by **radial spokes**.
- In the "9 + 2" arrangement, there are **9 radial spokes** connecting the peripheral doublets to the central sheath.
- The central sheath is a structure that encases the central pair of microtubules.

5. **Analyzing the Options**:
- **Option A**: Incorrect, as it states 9 + 0 central microtubules.
- **Option B**: Incorrect, as it states 9 + 2 but incorrectly describes the arrangement.
- **Option C**: Correct, as it accurately states 9 peripheral microtubules, 2 central microtubules, 9 radial spokes, and 1 central sheath.
- **Option D**: Incorrect, as it states only 3 peripheral microtubules.

6. **Conclusion**:
- The correct answer is **Option C**: Peripheral microtubules = 9, Central microtubules = 2, Radial spokes = 9, Central sheath = 1.

### Final Answer:
**Option C**: Peripheral microtubules = 9, Central microtubules = 2, Radial spokes = 9, Central sheath = 1.

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