Question

Bio HW

27

Why have domains been added to the present system of classification?

	a.	Additional information has been gained from molecular (DNA) studies.
	b.	There are so many differences between Eubacteria and Archaea that it is necessary to divide them.
	c.	Fossils of bacteria have been found that differ from organisms alive today.
	d.	Distantly related organisms have been found to resemble one another.
	e.	Both A and B are correct.

Answer 1

In 1990, Carl Woese gave the three domains system of classification of living organisms. This classification was based on the molecular study of the different organisms. This model of classification was based on the nucleotide sequence of cell's ribosomal rRNA, membrane lipid structure and sensitivity to antibiotics. This classification was important because some organisms which were previously characterised together, were found to be genetically very different. Hence, option e is correct.