85.The answer is a.(Junqueira, pp 42–44, 46, 71, 471–474.)The centriole
consists of nine microtubule triplets arranged together by linking proteins
to form a cartwheel arrangement. Microtubules are found in different struc-
tural patterns within the cell. The basal body is a centriole-like structure
associated with the ciliary axoneme. It too has a nine-triplet arrangement of
microtubules. Cytoplasmic microtubules (answer b)are found in the sin-
glet form and undergo constant association and dissociation of tubulin at
their plus ends and minus ends, respectively. Flagella (answer c)have the
same “9+2” arrangement as cilia, but are limited to one per cell and in adult
humans are found only in sperm. The axoneme (answer d)has the classic
“9+2” arrangement of microtubules. Stereocilia (answer e)are large, mod-
ified microvilli, found in the epididymis and on hair cells in the organ of
Corti, therefore, they are not composed of microtubules.
170 Anatomy, Histology, and Cell Biology