What role does the definitive host play in the lifecycle of tapeworms?

The definitive host plays a crucial role in the lifecycle of tapeworms as it is the organism in which the adult tapeworm resides and reproduces. Tapeworms, which belong to the class Cestoda, have complex lifecycles that typically involve both definitive and intermediate hosts. In the definitive host, the tapeworm attaches to the intestinal wall and matures into its adult form, where it engages in sexual reproduction, producing eggs that get released into the environment.

This option highlights the key aspect of the tapeworm's lifecycle: the transition from juvenile forms, which often develop in intermediate hosts, to adulthood and reproduction in the definitive host. The definitive host thus serves not only as the habitat for the fully developed tapeworm but also facilitates the continuation of the tapeworm species by allowing it to reproduce and spread its eggs, which will eventually infect new intermediate hosts or definitive hosts.