Which term describes a living or once-living organism in an ecosystem?

The term that describes a living or once-living organism in an ecosystem is "biotic." In ecological contexts, biotic factors include all the living organisms, such as plants, animals, fungi, and microorganisms, that interact with one another and their environment. These interactions can include predation, competition, symbiosis, and various forms of reproduction.

Abiotic factors, on the other hand, refer to the non-living components of an ecosystem, such as sunlight, temperature, water, and minerals, which influence the environment and the organisms living within it. The terms "bioreactor" and "biohazard" refer to specific applications or conditions related to biology and do not pertain to the classification of organisms within ecosystems. A bioreactor is a device or vessel that provides a controlled environment for bioprocesses, while a biohazard indicates a risk to health or the environment from biological substances. Thus, "biotic" is the appropriate term for describing living or once-living organisms in an ecosystem.