Which of the following best describes methanogens?

• A. They are viruses.
• B. They are eukaryotic microorganisms.
• C. They are multicellular fungi.
• D. They are prokaryotic microorganisms.

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the term 'methanogens' — these are microorganisms known for producing methane as a metabolic byproduct in anoxic conditions.
2. Step 2: Recall the three domains of life: Bacteria, Archaea, and Eukarya. Methanogens belong to the domain Archaea, which are prokaryotic microorganisms.
3. Step 3: Recognize that prokaryotic microorganisms lack a nucleus and membrane-bound organelles, distinguishing them from eukaryotic microorganisms.
4. Step 4: Eliminate incorrect options: methanogens are not viruses (which are acellular and not living cells), not eukaryotic microorganisms (which have nuclei), and not multicellular fungi (which are eukaryotic and multicellular).
5. Step 5: Conclude that methanogens are best described as prokaryotic microorganisms, specifically archaea that produce methane.