Any organism that lives on or in a host at the expense of that host is called a aerobe anaerobe parasite pathogen

The correct term for an organism that lives on or in a host at the expense of that host is a **parasite**. **Explanation of the Options:** 1. **Aerobe**: An organism that requires oxygen to survive. 2. **Anaerobe**: An organism that does not require oxygen for survival. 3. **Parasite**: An organism that lives on or in a host organism and benefits at the host's expense. 4. **Pathogen**: An organism that causes disease in its host. While both **parasites** and **pathogens** involve interactions with a host, the key distinction is that parasites derive nutrients and benefits directly from the host, typically harming it in the process. Pathogens specifically refer to organisms that cause disease, which may not always involve the same level of dependency or exploitation as parasites. **Correct Answer:** parasite