Final answer:
Methanogen Archaea bacteria reduce carbon dioxide to methane as a part of their anaerobic respiration process, helping them to generate energy in the form of ATP while also affecting the environment as methane is a greenhouse gas.
Step-by-step explanation:
Methanogen Archaea bacteria take carbon dioxide and reduce it to methane. These microorganisms utilize anaerobic respiration to convert CO2 to CH4 in environments where oxygen is not present, such as soil and the digestive tracts of ruminants like cows and sheep. This process is not only critical for the organism's survival by generating ATP, but it also has significant environmental implications due to methane being a potent greenhouse gas. Nonetheless, methanotrophs play a role in reducing atmospheric methane, thus mitigating the greenhouse effect to some extent.