Which of the following statements regarding cilia is not correct

Options

A. The organized beating of cilia is controlled by fluxes of `Ca^(2+)` across the membrane
B. Cilia are hair-like cellular appendages
C. Microtubules of cilia are composed of tubulin
D. Cilia contain an outer ring of nine doublet microtubules surrounding two single microtubules

Answer

To determine which statement regarding cilia is not correct, we will analyze each option provided:

### Step-by-step Solution:

1. **Understanding Cilia**:
- Cilia are hair-like structures that extend from the surface of certain cells. They play a role in movement, either propelling the organism or moving substances across the cell surface.

2. **Analyzing Option A**:
- **Statement**: "The organized beating of cilia is controlled by fluxes of calcium ion across the membrane."
- **Analysis**: This statement is incorrect. The beating of cilia is primarily controlled by the action of dynein motor proteins, which utilize ATP for energy, rather than being directly controlled by calcium ion fluxes.

3. **Analyzing Option B**:
- **Statement**: "Cilia are held like cellular appendages."
- **Analysis**: This statement is correct. Cilia are indeed cellular appendages that extend from the cell surface.

4. **Analyzing Option C**:
- **Statement**: "Microtubules of cilia are composed of tubulin."
- **Analysis**: This statement is correct. The microtubules that make up cilia are composed of tubulin proteins.

5. **Analyzing Option D**:
- **Statement**: "Cilia contain an outer ring of 9 doublet microtubules surrounding two single microtubules."
- **Analysis**: This statement is also correct. Cilia have a characteristic structure known as the "9+2" arrangement, where there are 9 doublet microtubules surrounding 2 central single microtubules.

6. **Conclusion**:
- The only incorrect statement regarding cilia is Option A. Therefore, the answer to the question is **Option A**.