Doublet fibrils of a cilium or flagellum are tilted at an angle of

Options

A. (a) `5^(@)`
B. (b) `10^(@)`
C. (c) `15^(@)`
D. (d) `20^(@)`

Answer

To answer the question regarding the angle at which the doublet fibrils of a cilium or flagellum are tilted, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of Cilia and Flagella**:
- Cilia and flagella are cellular appendages that have a characteristic structure composed of microtubules. They are important for cell movement and fluid movement across the cell surface.

2. **Identify the Composition of Doublet Fibrils**:
- The doublet fibrils refer to the arrangement of microtubules in the peripheral structure of cilia and flagella. There are typically nine outer doublet microtubules arranged in a circular pattern.

3. **Recognize the Angle of Tilt**:
- The question specifically asks about the angle at which these doublet fibrils are tilted. It is important to note that in the structure of cilia and flagella, these doublet microtubules are not arranged perfectly parallel but are tilted.

4. **Determine the Correct Angle**:
- Based on the knowledge of ciliary and flagellar structure, it is established that the doublet fibrils are tilted at an angle of 10 degrees.

5. **Select the Correct Option**:
- Given the options provided (5 degrees, 10 degrees, 15 degrees, and 20 degrees), the correct answer is 10 degrees, which corresponds to option B.

### Final Answer:
- The doublet fibrils of a cilium or flagellum are tilted at an angle of **10 degrees** (Option B).