What does the 9 + 2 arrangement of microtubules refer to in structures of cilia and flagella?

• A. The microtubules' length.
• B. The microtubules' association with the basal body.
• C. The microtubules' arrangement in the axoneme.
• D. The microtubules' arrangement embedded in the cytoplasmic membrane.

Answer: (C)

Verified step by step guidance

1. Understand that cilia and flagella are hair-like structures that protrude from the surface of eukaryotic cells and are involved in movement.
2. Recognize that the '9 + 2 arrangement' refers to the specific structural organization of microtubules within the axoneme, which is the central shaft of cilia and flagella.
3. The axoneme is composed of nine doublet microtubules arranged in a circle around two central single microtubules, hence the term '9 + 2'.
4. This arrangement is crucial for the bending and movement of cilia and flagella, as the dynein arms attached to the microtubules generate force through ATP hydrolysis.
5. The basal body anchors the axoneme to the cell and is structurally similar to a centriole, but the '9 + 2' arrangement specifically describes the axoneme's internal structure, not the basal body or the microtubules' length.