Final answer:
Archaea, specifically methanogens, thrive in anaerobic environments by using CO2 to produce methane during anaerobic respiration.
Step-by-step explanation:
Some members of the group of organisms that thrive in anaerobic environments are archaea. Among the archaea, the group known as methanogens are particularly adept at surviving without oxygen. Methanogens use CO2 as their final electron acceptor during anaerobic respiration, producing methane (CH4), a process vital for their energy production and survival in such anaerobic conditions. These microorganisms can be found in a variety of environments, including soil and the digestive tracts of ruminants like cows and sheep. They are known for their ability to live in harsh conditions and are considered extremophiles.