A parasitic organism is defined as one that does which of the following?

A parasitic organism is characterized by its dependency on another organism, known as the host, for its survival. This relationship usually involves the parasite feeding on the host's nutrients, which can often lead to harm for the host. In this context, the correct answer emphasizes that a parasitic organism not only relies on another for sustenance but also often inhabits it, deriving shelter and resources. This is a fundamental aspect of parasitism, distinguishing it from other ecological relationships, like mutualism, where both organisms benefit, or commensalism, where one benefits without harming the other.

The other options suggest relationships that do not accurately reflect the nature of parasitism. For instance, contributing to the host's survival or being beneficial to the host describes mutually beneficial relationships, while surviving independently indicates a free-living organism rather than a parasitic one.