Question

Which of the following statements regarding cilia is not correct?
A. Cilia contain an outer of nine doublet microtubules surrounding two single microtubules.
B. The organized beating of cilia is controlled by fluxes of \[C{{a}^{2+}}\] across the membrane.
C. Cilia are hair-like cellular appendages.
D. Microtubules of cilia are composed of tubulin.

Answer 1

Hint: Cilia are cell organelles for locomotion. Cilia are found in species such as paramecium, while flagella are also present in bacteria and sperm cells. They're shorter and numerous.

Complete answer: Cilia is a vibratile, cytoplasmic, fine hair-like structures present in some cells. They are surrounded by a membrane unit, which is the extension of the plasma membrane of the cell. A fluid matrix with a supporting axial shaft, or axoneme, is within the membrane. Eleven microtubules are made of axonemes. Two microtubules are single and lie in-between the middle of the gap. They're referred to as central singlets. The remaining nine are doubled microtubules that lie in a circle around the central microtubules. Sub tubules A and B are referred to as the two microtubules that form a doublet. Microtubules, both single and double are composed of the globulin protein units. The microtubule arms of A contain the protein dynein. The latter is the enzyme ATPase which catalyzes \[ATP\] hydrolysis to \[ADP\] and transfers free energy directly to the ciliary function. A cytoskeleton based on microtubules is called an axoneme inside the cilia. In addition to the nine outer doublets, called the \[9+2\] axoneme, cilia axoneme has a ring of nine outer microtubules and two central microtubules. However, the synchronized beating of cilia is triggered by the regulated sliding of the external duplicate microtubules.
Hence, the correct answer is option B.

Note: The distinction between cilia and flagella is very simple. Structurally, they are distinct and have several patterns of movement. There are also various variations in cilia and flagella that serve different functions. Flagella and cilia have the same axoneme structure despite their distinct names, including nine double microtubules arranged during rotation around two central singlet microtubules.