What type of organism typically harms its host?

The correct answer is that a parasite typically harms its host. Parasites are organisms that live on or in a host and benefit at the host's expense. They derive nutrients and other benefits from their hosts while often causing harm, which can range from minor irritation to severe disease or even death. This harmful interaction is a fundamental characteristic that distinguishes parasites from other types of organisms.

In contrast, symbiotes often have a mutually beneficial relationship with their hosts, where both parties gain advantages from the interaction. Predators, on the other hand, hunt and kill their prey for sustenance but do not usually live in or on them as parasites do. Commensals live in close association with their hosts but do not cause harm, instead, they may provide some benefit without impacting the host negatively. This distinction underscores why parasites are specifically defined by their harmful relationship with their hosts.