Final answer:
The incorrect statement about cilia is that they contain two single microtubules in their center. In reality, cilia have a 9 + 2 arrangement with nine doublet microtubules surrounding two central singlet microtubules.
Step-by-step explanation:
The statement that is not correct about cilia is: A. Cilia contain an outer of nine doublet microtubules surrounding two single microtubules. This is incorrect because cilia (and flagella) possess a structure known as a "9 + 2 array", which consists of a ring of nine doublet microtubules surrounding two central singlet microtubules, not two single microtubules as the statement suggests.
Microtubules of cilia are indeed composed of tubulin and are responsible for the maintenance of cell shape and structure, providing rigidity and organization. Stretching across the cell, these microtubules also make up the appendages necessary for cellular motion, such as cilia and flagella.
The beating of cilia is rhythmic and driven by motor proteins, such as dynein, which facilitate motion along these microtubules. The organized beating is indeed controlled by fluxes of Ca²⁺ across the plasma membrane, contributing to the locomotion and various other functions cells perform with these appendages. Lastly, cilia are indeed hair-like cellular appendages found on many cells, especially epithelial cells, and play a crucial role in movement and clearing debris in numerous biological systems, such as the respiratory tract.