Final answer:
The motor protein dynein is responsible for transporting building materials to the tip of a growing axoneme during the formation of a cilium or flagellum.
Step-by-step explanation:
When a cilium or a flagellum emerges from a basal body, the motor protein dynein moves building materials to the assembly site at the tip of the growing axoneme. Microtubules in eukaryotic flagella and cilia originate from a basal body and align within the structure to form an axoneme. This axoneme is enveloped by the plasma membrane and typically exhibits a '9+2' arrangement, which consists of nine paired doublets of microtubules encircling two central single microtubules.
Dynein arms connected to the microtubules facilitate the movement and bending of the cilium or flagellum during its assembly and function.