The prokaryotic cells that built stromatolites are classified as proteobacteria, chlamydias, and spirochetes. Which group was not described in Woese’s tree of life analysis? Archaea, Bacteria, Prokarya, Eukaryas, gram-positive bacteria, and cyanobacteria.
The Correct Answer and Explanation is:
Correct Answer: Prokarya
Explanation
The correct answer is Prokarya, as this is not a recognized domain in Woese’s tree of life. Carl Woese’s groundbreaking work in the late 1970s used ribosomal RNA (rRNA) sequences to classify all life into three domains: Bacteria, Archaea, and Eukarya. This molecular phylogenetic analysis revolutionized our understanding of the relationships among organisms and replaced older classification systems based primarily on morphology and metabolism.
Prior to Woese’s research, all organisms without a nucleus were grouped together as prokaryotes, contrasted with eukaryotes, which have a nucleus and other membrane-bound organelles. The term “Prokarya” (or “Prokaryota”) was used to refer to this broad category. However, Woese demonstrated that prokaryotes are not a single, unified group; instead, they consist of two very different lineages: Bacteria and Archaea. These lineages are as distinct from each other as they are from Eukarya.
In Woese’s three-domain system:
- Bacteria includes familiar groups like cyanobacteria, proteobacteria, gram-positive bacteria, spirochetes, and chlamydias.
- Archaea comprises ancient prokaryotes that often live in extreme environments and differ from bacteria in genetics and cell structure.
- Eukarya includes all eukaryotic organisms such as plants, animals, fungi, and protists.
Thus, groups like cyanobacteria, proteobacteria, and gram-positive bacteria are part of the Bacteria domain. Chlamydias and spirochetes are also bacterial groups. Archaea and Eukarya are valid domains in Woese’s tree.
However, Prokarya is not included because Woese’s analysis proved it was an artificial grouping that does not reflect true evolutionary relationships. Therefore, Prokarya was rejected as a formal taxonomic category in modern systematics.
