Question

The drawback of the three-domain system of classification is
A. The sequence of features and polygenes from highly conserved proteins are inconsistent
B. Viruses are not classified
C. Both the gram-negative bacteria and archaea have monoderm but classified in a different group
D. Both A and C

Answer 1

Hint:-The three-domain classification with six kingdoms is the latest system of classification. It was proposed by Carl Woese in 1990. The three domains of this system include archaea, bacteria, and eukaryote. The six kingdoms are Archaebacteria, Eubacteria, Protista, Fungi, Plantae, and Animalia. The kingdom Archaebacteria is the new addition to the previous five-kingdom classification by RH Whittaker.

Complete step-by-step solution:-The three-domain classification is based on three distinct characters that include differences in 16 S ribosomal RNA (ribonucleic acid) sequencing, differences in the cell membrane structure, and sensitivity to antibiotics. The use of 16 S rRNA was better than DNA because it evolves very slowly and is universally the same.
The first domain archaea include all the prokaryotes, unicellular organisms that do not have a nuclear membrane. The archaea differ from the eubacteria in not having peptidoglycan (polysaccharide) in their cell wall. They have pseudo murein in their cell wall. They are ancient bacteria and can survive in adverse conditions such as excessive salty marshes (halophiles), geothermal hot springs (thermophiles), extreme cold temperature (psychrophilic),
The second domain includes the Eubacteria or true bacteria that have peptidoglycan in their cell wall. But gram-negative bacteria have similar cell wall composition as the Archaebacteria but are placed in a different domain, therefore it is one drawback of this classification. The third domain includes all the eukaryotes that have a membrane-bound nucleus. These include Protists such as euglena, fungi such as mushrooms, plants, and animals.
The viruses are not included in any biological classification as they are not living organisms. They only have genetic material inside a protein coat and do not show any metabolism or reproduction. Therefore it cannot be considered as a drawback of this classification.This classification has an inconsistent sequence of features and polygenes and therefore the correct answer is D

Note:-
The three-domain classification is different from the three kingdom classification proposed by Ernst Haeckel. This classification includes only Protista, Plantae, and Animalia. There is no mention of Eubacteria and Archaebacteria. This classification was proposed in the 1860s. Then came the 4 kingdom classification by Copeland and he included Monera or bacteria.