A parasite that relies on a host for its survival is known as an obligate parasite. These organisms depend entirely on their host for nutrients, reproduction, and survival, often causing harm to the host in the process. Common examples include tapeworms, leeches, and certain types of fungi and bacteria. Obligate parasites have evolved specialized adaptations that allow them to thrive within their hosts while evading the host's immune responses. This type of relationship can significantly impact the host's health and population dynamics.