Question

The three domain system with six kingdoms is the latest classification based on
A)Mitochondrial genes
B)Nuclear genes
C)16S rRNA gene
D)Chloroplast gene

Answer 1

Hint: RH Whittaker proposed five-kingdom classification. This was based on the characteristics such as cell structure, reproduction and mode of nutrition as well. Two kingdoms named Monera and Protista were included in this classification. Monera kingdom includes prokaryotic organisms and kingdom protists include single-celled eukaryotes.

Complete answer:
The three-domain system was firstly introduced by Carl Woese in 1990. It is also known as Carl Woese’s Classification. This system is also known as Six Kingdoms and Three Domains Classification because it divides the life forms into three domains and six kingdoms.
Three-domains of Carl Woese’s Classification system includes archaea, bacteria, eukaryotes, and the kingdoms are Archaebacteria, Eubacteria, Protista, Fungi, Plantae and Animalia.

This classification system divides life based on the differences in the 16S ribosomal RNA structure, the cell’s membrane lipid structure and its sensitivity to antibiotics. The main difference from earlier classification systems is the splitting of archaea from bacteria.

The evaluating rRNA structure is important. As a result of rRNA molecules, throughout nature perform the identical function, their structure modifications vary over time. The similarities and dissimilarities in rRNA nucleotide sequences indicate the associated or unrelated completely different cells and organisms are.

In this classification, Carl Woese used 16S ribosomal RNA (rRNA) as a Chronometer because of the following reasons.
1)It is universally distributed
2)It is functionally similar in all organisms
3)It can change its sequence slowly
4)Its sequences can be aligned, or matched up, between two organisms.

Domain Archaea: It includes prokaryotic cells. They lack nuclear membrane, possess distinct biochemistry; contain RNA markers from bacterial cells. Archaea are considered as the oldest species of organisms on Earth. They have the ability to survive in extreme and harsh environments. The cell wall of archaea lacks peptidoglycan. Archaea has three phyla: Crenarchaeota, Euryarchaeota, Konarchaeota

Domain Bacteria: These are also prokaryotic cells with bacterial rRNA and contain diacyl glycerol diester lipids in their membrane. They are also called eubacteria or true bacteria. Their cell membrane contains ester linkage between unbranched fatty acid chains and glycerol. Their cell wall is made up of peptidoglycan. There are 5 phyla of the bacterial domain: Proteobacteria, Cyanobacteria, Eubacteria, Chlamydias, Spirochaetes

Domain Eukarya: These are eukaryotic cells with membrane-bound nuclei. They do not have peptidoglycans on their cell wall. Eukarya inhibits antibacterial antibiotics but is sensitive to antibiotics which affect the eukaryotic cells. There are four Kingdoms of Eukarya: Protista, Fungi, Plantae, and Animalia.

Hence, the correct answer is option (C)

Note: The earliest classification was based on the uses of organisms. The branch of Science dealing with the classification and relationship of organisms is known as systematics. Carl Linnaeus was one of the first scientists who gave binomial nomenclature.