This set of Microbiology Multiple Choice Questions & Answers (MCQs) focuses on “Microbial Classification”.
1. Type strain is used for referring to?
a) species
b) genus
c) family
d) division
View Answer
Explanation: Bacterial species consists of a special strain called type strain which have similar characteristics. Bacterial genus is composed of a collection of similar species and is referred to as type species.
2. The correct order of taxonomic groups from higher to lower rank is?
a) Kingdom—Order—Class—Family
b) Order—Class—Division—Family—Genus—Species
c) Kingdom—Order—Division—Family—Class—Genus—Species
d) Kingdom—Division—Class—Order—Family—Genus—Species
View Answer
Explanation: Taxonomists have made the classification based on two qualities—stability and predictability. The order of taxonomic groups from higher rank to lower rank is: Kingdom—Division—Class—Order—Family—Genus—Species.
3. % Similarity (%S) of each strain to every other strain is calculated by which method?
a) Intuitive Method
b) Numerical Taxonomy
c) Genetic Relatedness
d) DNA homology experiments
View Answer
Explanation: %S = NS
NS+ND
where, %S is % similarity of each strain to every other strain, NS is the number of characteristics that are the same for the two strains, and ND is the number of characteristics that are different. Thus this is determined by numerical taxonomy.
4. Two organisms which are very closely related to each other have which of the following property?
a) similar mol% G+C values
b) different mol% G+C values
c) similar mol% G+C values and heteroduplexes are formed
d) different mol% G+C values and heteroduplexes are not formed
View Answer
Explanation: Two organisms of the same species that are very closely related to each other will have very similar mol% G+C values and their single strands of DNA molecules combine to form heteroduplexes. Organisms which are not closely related have different mol% G+C values and hence do not form heteroduplexes.
5. What are ribosomes composed of?
a) Proteins
b) DNA
c) RNA
d) Proteins and RNA
View Answer
Explanation: Ribosomes, the small granular-appearing structures within the cell which manufacture proteins, are composed of proteins and RNA. The ribosomal RNA (rRNA) is coded for by only a small fraction of the DNA molecule, the rRNA cistrons.
6. If two organisms are distantly related and show no DNA homology there still may be similarity in their rRNA cistrons.
a) True
b) False
View Answer
Explanation: The nucleotide sequence of rRNA genes has been found to be highly conserved. So even if two organisms are only distantly related and show no significant DNA homology, there still maybe similarity in the nucleotide sequences of their rRNA cistrons. The degree of similarity that exists can then be used as a measure of relatedness between organisms.
7. Which of the following are characteristics of archaebacterial different from eubacteria?
a) methane-producers
b) extreme halophiles
c) thermoacidophiles
d) methane-producers, extreme halophiles, and thermoacidophiles
View Answer
Explanation: Eubacteria are the traditional, familiar ones that have received the most study. Archaebacteria the other group consists of methane producers, extreme halophiles and thermoacidophiles.
8. Which among the following come under Gram-positive eubacteria?
a) Clostridium
b) Actinomyces
c) Rhizobium
d) Clostridium, Actinomyces
View Answer
Explanation: Based on rRNA oligonucleotide, Clostridium and Actinomyces come under Gram-positive eubacteria. Rhizobium belongs to Purple eubacteria.
9. Which among the following kingdoms were proposed by Whittaker?
a) Monera
b) Protista, Fungi
c) Plantae, Animalia
d) Monera,Protista,Fungi,Plantae,Animalia
View Answer
Explanation: R.H.Whittaker classified microorganisms on the basis of nutritional requirements and formed Whittaker’s Five Kingdom and they are Monera (bacteria and cyanobacteria), Protista (microalgae and protozoa), Fungi (yeasts and molds), Plantae (multicellular green plants and higher algae) and Animalia (multicellular animals).
10. According to Bergey’s Manual of Systematic Bacteriology, prokaryotes that lack a cell wall belong to the group?
a) Gracilicutes
b) Firmicutes
c) Tenericutes
d) Mendosicutes
View Answer
Explanation: Tenericutes are prokaryotes that lack a cell wall. Gracilicutes are prokaryotes with a complex cell-wall structure characteristic of Gram-negative bacteria. Firmicutes are prokaryotes with a cell wall structure characteristic of Gram-positive bacteria and Mendosicutes are prokaryotes that show evidence of an earlier phylogenetic origin.
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