Final answer:
Extremophiles refer to unicellular organisms, which include prokaryotes such as bacteria and archaea, that are capable of surviving in extreme environmental conditions. These can range from high salinity and acidity to extreme temperatures and radioactivity. They are key in understanding life's diversity and have potential applications in medical and industrial fields.
Step-by-step explanation:
The related group of unicellular organisms that thrive under extremely harsh environmental conditions are known as extremophiles. These organisms, which can be either prokaryotic or eukaryotic, have adapted to live in habitats ranging from deep ocean vents to hot springs, and from arctic ice to extremely saline, acidic, or radioactive environments.
Among these, the domain Archaea is particularly noteworthy, with many of its members classified as extremophiles. These organisms give insight into the diversity of life and have applications in finding new therapeutic drugs or industrial processes.
The category includes a variety of forms such as halobacterium, which requires high salt concentrations, and others which may be halophilic (salt-loving), alkaliphilic (preferring high pH environments), or thermophilic (heat-loving).