Q.11 Which one of the following DOES NOT belong to the domain of Bacteria?
- (A) Cyanobacteria
- (B) Proteobacteria
- (C) Bacteroids
- (D) Methanobacterium
The three-domain system classifies life into Bacteria, Archaea, and Eukarya based on rRNA phylogeny. Bacteria feature peptidoglycan cell walls and distinct membranes. This article solves the MCQ, pinpointing (D) Methanobacterium as the non-Bacteria.
Three Domains Overview
Bacteria encompass diverse phyla with Gram-positive/negative traits. Archaea, like methanogens, share prokaryotic form but differ in membrane lipids (ether-linked) and rRNA loops. Eukarya have nuclei.
Correct Answer: (D) Methanobacterium
Methanobacterium is an Archaea methanogen producing CH4 from CO2/H2. It lacks peptidoglycan (uses pseudomurein), confirming Archaea domain despite “bacterium” name.Explanation of All Options
Domain assignment for each:
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(A) Cyanobacteria
Bacteria. Phylum Cyanobacteriota; oxygenic photosynthesizers with thylakoids, like Anabaena. -
(B) Proteobacteria
Bacteria. Largest phylum (Alphaproteobacteria to Deltaproteobacteria); includes E. coli, Rhizobium. -
(C) Bacteroids
Bacteria. Phylum Bacteroidota; Gram-negative anaerobes in guts, degrade carbs (e.g., Bacteroides fragilis). -
(D) Methanobacterium
Archaea. Methanobacteria class, Euryarchaeota phylum; strict anaerobes in rumen/biogas.
Option Domain Key Trait Habitat Example (A) Cyanobacteria Bacteria Photosynthesis Aquatic (B) Proteobacteria Bacteria Diverse metabolism Soil, gut (C) Bacteroids Bacteria Polysaccharide degradation Human microbiome (D) Methanobacterium Archaea Methanogenesis, pseudomurein Anaerobic digesters Microbiology Relevance
Distinguishing domains aids antibiotic design—Archaea lack bacterial targets. For biotech, methanogens fuel biofuel production. Analyze 16S rRNA with BLAST to confirm classifications in your studies.
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