A cilium beats

Options

A. Asymmetrically by sweeping action
B. Symmetrically by sweeping action
C. Symmetrically by undulatory action
D. Asymmetrically by undulatory action

Answer

**Step-by-Step Solution:**

1. **Understanding Cilia**: Cilia are tiny hair-like structures found on the surface of certain cells. They play a crucial role in various biological processes, including movement and the clearing of mucus in the respiratory tract.

2. **Function of Cilia**: The primary function of cilia is to move fluid or mucus across the cell surface. In the respiratory tract, cilia help sweep mucus that traps dust and bacteria out of the airways.

3. **Beating Pattern of Cilia**: Cilia beat in a specific pattern that can be classified into two types of strokes:
- **Effective Stroke**: This is the stroke where the cilia are straight and generate a strong flow in one direction. This stroke is responsible for moving mucus effectively.
- **Recovery Stroke**: In this stroke, the cilia return to their original position, usually parallel to the surface, and create a weaker backflow. This stroke is less forceful and helps reset the cilia for the next effective stroke.

4. **Asymmetrical Beating**: The combination of the effective and recovery strokes results in an asymmetrical beating pattern. This means that the cilia do not beat in a uniform manner but rather in a coordinated way that allows for effective movement of substances.

5. **Conclusion**: Based on the understanding of cilia and their beating mechanism, the correct answer to the question "A cilium beats" is option A: asymmetrically by sweeping actions.

**Final Answer**: A cilium beats asymmetrically by sweeping actions.

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