Final answer:
Parasites require an intermediate host to develop into an adult and reproduce. Roundworms, tapeworms, and flukes are examples of parasites that rely on intermediate hosts for their life cycle. These parasites have complex life cycles and often require multiple hosts.
Step-by-step explanation:
Parasites are organisms that live in or on another organism and derive nutrients from it. They have a complex life cycle that often involves multiple hosts. In order to develop into an adult and reproduce, parasites typically need an intermediate host. This is a host in which the parasite goes through some stages of its life cycle before migrating to the definitive host.
For example, roundworms are parasites that infect mammals, including humans. They produce large numbers of eggs, which are passed in the host's feces. Other individuals can become infected with roundworms by swallowing these eggs in contaminated food or water. In this case, the contaminated food or water serves as the intermediate host for the roundworms, allowing them to continue their life cycle.
Similarly, tapeworms and flukes are parasites that require multiple hosts to complete their life cycle. Tapeworms, for instance, cause disease in humans when contaminated, undercooked meat is consumed. The tapeworm then lives inside the intestine of the host, benefiting from the host's food. To complete its life cycle, the tapeworm moves from one host species to another.