State the names of the three domains, giving a microbial example of each.

Traditional classification separates organisms into two groups: prokaryotes and eukaryotes. Explain the reasons for reclassification of life into three domains.

Distinguish between the two domains of prokaryotes.

Eubacteria/Bacteria: E. coli / Pneumococcus / another suitable example; (scientific/common name acceptable)
Archaea: methanogens / thermophiles / another suitable example;
Eukaryota: Paramecium / yeast / another suitable example;

large diversity of the group categorized as prokaryotes prompted division into two domains;
similarities between Archaea more similar to Eukaryota than to Eubacteria;
facilitates study of origin/evolution of eukaryotes;

Archaea have different rRNA to Eubacteria;
Eubacteria have no proteins associated with DNA whereas Archaea have / vice versa;
introns are present in some genes of Archaea, but are rare/absent from Eubacteria;
cell walls are made of peptidoglycan in Eubacteria but not in Archaea;
cell membranes are made of different molecules / Eubacteria have glycerol-ester lipids whereas Archaea have glycerol-ether lipids;

N/A

F2 (b) was another difficult explanation question, although many candidates knew that the great diversity in prokaryotes prompted the new classification.

N/A