Why is Plasmodium classified as a parasite?

Plasmodium is classified as a parasite because it lives within a host organism, specifically within the red blood cells of humans, and causes harm to the host in the process. Parasites derive nutrients and energy from their hosts, which is a crucial characteristic that allows them to survive and reproduce. In the case of Plasmodium, the invasion of red blood cells leads to various health issues, including malaria, which can be severe and even fatal if left untreated. This harmful interaction highlights the nature of Plasmodium as a parasite, as it relies on the host for sustenance while adversely affecting the host's health. This distinguishes parasites from other organisms that may have different modes of living, such as mutualists or commensals, which do not inflict damage on their hosts.