The arrangement of microtubules in a flagellum and a centriole is as follows:

Flagellum:
The correct arrangement of microtubules in a flagellum is 9 + 2. This means that there are nine outer doublet microtubules arranged in a ring around two central singlet microtubules. The outer doublet microtubules are connected to each other by radial spokes and dynein arms, which allow for movement and bending of the flagellum. The central singlet microtubules provide structural support and stability.

Centriole:
The correct arrangement of microtubules in a centriole is 9 + 0. This means that there are nine triplets of microtubules arranged in a ring without any central microtubules. Each triplet consists of three microtubules: one complete microtubule and two incomplete microtubules. The centriole plays a crucial role in cell division, specifically in the formation of the mitotic spindle during mitosis.

Explanation for the correct answer (option D):

The correct answer is option D, which states that the arrangement of microtubules in a flagellum is 9 + 2, and in a centriole is 9 + 0. This answer is correct based on the known structural characteristics of flagella and centrioles.

- Flagellum: The arrangement of microtubules in a flagellum is indeed 9 + 2. This arrangement provides the necessary structure and flexibility for flagella to move and propel cells. The nine outer doublet microtubules, along with the radial spokes and dynein arms, allow for the sliding movement of microtubules, resulting in the bending and beating motion of the flagellum. The two central singlet microtubules provide stability and support to the flagellum.

- Centriole: The arrangement of microtubules in a centriole is indeed 9 + 0. This arrangement consists of nine triplets of microtubules arranged in a ring without any central microtubules. The centriole is involved in various cellular processes, including cell division. During cell division, centrioles play a crucial role in organizing and anchoring the mitotic spindle, which is responsible for separating chromosomes during mitosis.

In conclusion, the correct arrangement of microtubules in a flagellum is 9 + 2, while in a centriole, it is 9 + 0. This arrangement is essential for the proper functioning and structural integrity of both flagella and centrioles.