Category: MICROBIOLOGY Objective Questions

Microbiology Multiple Choice Questions on “Viruses of Bacteria – Lysogeny and Lytic”.

1. What does a viral DNA becomes after being associated with the bacterial chromosome?
A. gene
B. prophage
C. plasmid
D. plaque
Answer: B
Clarification: In lysogeny the viral DNA of the temperate phage, instead of taking over the functions of the cell’s genes, is incorporated into the host DNA and becomes a prophage in the bacterial chromosome, acting as a gene.

2. In which of the following method, the viral particles are transmitted through lysis of cell?
A. Lytic cycle
B. Lysogeny
C. Replication
D. Translation
Answer: A
Clarification: In the lytic cycle after the infection of bacterial cells by phages, the viral particles are transmitted through lysis of cell and finally terminates.

3. repressor protein makes the cell resistant to lysis.
A. True
B. False
Answer: A
Clarification: The temperate phage possesses a gene that codes for a repressor protein which makes the cell resistant to lysis initiated either by the prophage or by lytic infection by other viruses. The multiplication of the phage is repressed and lysogenization occurs.

4. Which of the following is the characteristic of repressor protein?
A. basic protein
B. acidic protein
C. basic protein, molecular weight of 26000
D. acidic protein, molecular weight of 26000
Answer: D
Clarification: The repressor protein is an acidic protein with a molecular weight of 26000. It has been isolated from lambda phage and purified.

5. cro gene is an example of an immunity repressor.
A. True
B. False
Answer: B
Clarification: Upon infection by lambda phage, the phage cro gene is transcribed, resulting in the synthesis of a protein repressor that inhibits the synthesis of the immunity repressor.

6. Which of the following gene codes for an enzyme which directs the insertion of the phage DNA into the bacterial chromosome?
A. recA gene
B. cro gene
C. int gene
D. gal gene
Answer: C
Clarification: A lambda phage enzyme, coded by the int gene, directs the insertion of the phage DNA into the bacterial chromosome. It catalyzes a single site-specific recombination event, resulting in the insertion of the phage DNA into the cell genome.

7. Which of the following phage do not cause lysogeny?
A. T2
B. T1
C. lambda
D. P1
Answer: A
Clarification: Phages like T2 that do not cause lysogeny are termed virulent. Phages produced by lysogenic strains are termed temperate phages, and the relationship between the phage and the bacterium is termed lysogeny.

8. The protein integrase is encoded by which of the following gene?
A. gal gene
B. lambda gene
C. bio gene
D. cro gene
Answer: B
Clarification: Integration of the lambda chromosome requires the action of a protein termed integrase encoded by a lambda gene and occurs at a 13 base pair region of DNA sequence homology between the bacterial and phage chromosomes.

9. In which of the following phage prophage exists as a circular form?
A. Phage lambda type
B. Phage P1 type
C. Phage T2 type
D. Phage T1 type
Answer: B
Clarification: In lysogeny of the P1 type, viral DNA does not normally become integrated into the host chromosome. Instead the prophage exists as a circular, self-replicating, double-stranded DNA element termed a plasmid.

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Microbiology Multiple Choice Questions on “Aquatic Environment”.

1. The moisture contained in clouds and precipitated as snow,hail,rain etc constitutes _________________
A. Atmospheric water
B. Surface water
C. Groundwater
D. Subterranean water
Answer: A
Clarification: The moisture contained in clouds and precipitated as snow, sleet, hail and rain constitutes atmospheric water. The air is washed by atmospheric water.

2. The surface waters are susceptible to contamination with microorganisms from _______________
A. the air
B. the surface runoff
C. precipitation
D. atmospheric water and the surface runoff
Answer: D
Clarification: The surface waters are susceptible to contamination with microorganisms from atmospheric water (precipitation), the surface runoff from soil and any wastes deliberately dumped into them.

3. Which of the following is subterranean water?
A. Atmospheric water
B. Surface water
C. Groundwater
D. Rainwater
Answer: C
Clarification: Groundwater is subterranean water that occurs where all pores in the soil or rock-containing materials are saturated.

4. Wells less than ___________ deep are considered to be shallow.
A. 1 ft
B. 100 ft
C. 50 ft
D. 1000 ft
Answer: B
Clarification: Wells are made by sinking a shaft into the ground to penetrate the groundwater level. Wells less than 100 ft deep are considered to be shallow.

5. Thermus aquaticus, a common bacterial inhabitant generally prevails in temperatures of ____________
A. 0⁰ C
B. 30-40⁰C
C. 70-72⁰C
D. 80-85⁰C
Answer: C
Clarification: Thermus aquaticus, a common bacterial inhabitant of hot springs has an optimum growth temperature of 70 to 72⁰C.

6. Hydrostatic pressure increases the boiling point of water but does not change the solubility of nutrients.
A. True
B. False
Answer: B
Clarification: Hydrostatic pressure increases the boiling point of water. It affects chemical equilibrium which in turn results in lowering of pH and a change in the solubility of nutrients such as bicarbonate.

7. Primary producers are found growing in which of the following layers of water?
A. upper layer
B. middle layer
C. intermediate layer
D. bottom layer
Answer: A
Clarification: In most aquatic habitats the primary producers i.e. algae have their growth restricted to the upper layers of waters through which light can penetrate.

8. The degree of salinity in freshwater is nearly zero.
A. True
B. False
Answer: A
Clarification: The degree of salinity in natural waters ranges from near zero in freshwaters to saturation in salt lakes.

9. The microorganisms from lakes and rivers can grow at a salt concentration of _________
A. 2.5 to 4 percent
B. 5 percent
C. below 1 percent
D. above 1 percent
Answer: C
Clarification: Microorganisms from lakes and rivers are salt sensitive and do not grow at a salt concentration of more than 1 percent whereas marine microorganisms are halophilic.

10. Which of the following compounds are required for the growth of saprophytic bacteria and fungi?
A. organic compounds
B. nitrates
C. phosphates
D. mercury
Answer: A
Clarification: Organic compounds are required for the growth of saprophytic bacteria and fungi whereas nitrates and phosphates are important for the growth of algae.

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Microbiology Multiple Choice Questions on “Bacterial Transduction”.

1. How much time is taken by the new DNA to make whole phage particles?
A. 24 hours
B. 60 mins
C. 2 mins
D. 10-20 mins
Answer: D
Clarification: Within 10 to 20 minutes, depending on the phage, the new DNA combines with the new proteins to make whole phage particles, which are released by the destruction of the cell wall and lysis of the cell.

2. When viral genome can become integrated into the bacterial genome they are known as ____________
A. temperate phage
B. prophage
C. bacteriophage
D. episome
Answer: B
Clarification: When viral genome can become integrated into the bacterial genome they are known as prophages. They carry DNA that can behave as a kind of episome in bacteria.

3. Bacteriophages inject their nucleic acid into the bacterium.
A. True
B. False
Answer: A
Clarification: Bacteriophages inject their nucleic acid usually DNA into the bacterium where it replicates rapidly and also directs the synthesis of new phage proteins.

4. Which of the following role is performed by a bacteriophage in transduction?
A. vector
B. donor
C. recipient
D. episome
Answer: A
Clarification: Bacterial transduction is the transfer by a bacteriophage, serving as a vector, of a portion of DNA from one bacterium (donor) to another (a recipient).

5. The viral DNA may be incorporated into the phage head during phage assembly.
A. True
B. False
Answer: B
Clarification: Any part of the bacterial chromosome may be incorporated into the phage head during phage assembly and is usually not associated with any viral DNA.

6. What is the frequency of defective phage particles in progeny phage produced?
A. 100
B. 10^-1
C. 10^-5
D. 1000
Answer: C
Clarification: The frequency of such defective phage particles is about 10^-5 to 10^-7 of the progeny phage produced.

7. Fragments transferred by a bacteriophage contains how many genes?
A. 20
B. 50
C. 1
D. 100
Answer: D
Clarification: Generalized transduction provides a means for mapping bacterial genes, since the fragments transferred by a bacteriophage are often large enough to contain 100s of genes.

8. What is the correct order when coliphage P1 is grown in a thr+ leu+ aziR host is used to infect a thr- leu- azi- recipient bacterial cell?
A. thr⁺ leu⁺ azi^R
B. thr^– leu⁺ azi^R
C. thr⁺ leu^– azi^R
D. thr^– leu^– azi^R
Answer: A
Clarification: When coliphage P1 is grown in a thr⁺ leu⁺ azi^R host is used to infect a thr^– leu^– azi^– recipient bacterial cell then if Leu⁺ recombinants are selected, about 50 percent of these are also Az^R.

9. How many percent of thr+ transducing phages also carry leu+?
A. 10%
B. 5%
C. 3%
D. 15%
Answer: C
Clarification: Only 3% of thr⁺ transducing phages also carry leu⁺ shows that these two genes are so far apart that they are rarely included at the same time in a DNA fragment that goes into the P1 head.

10. When the phage transduces only those bacterial genes adjacent to the prophage in the bacterial chromosome then it is known as?
A. generalized transduction
B. specialized transduction
C. restricted transduction
D. conjugation
Answer: C
Clarification: When the phage transduces only those bacterial genes adjacent to the prophage in the bacterial chromosome then it is known as restricted transduction.

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Microbiology Multiple Choice Questions on “Transmission and Scanning Electron Microscope”.

1. Which of the following is used in electron microscope?
A. electron beams
B. magnetic fields
C. light waves
D. electron beams and magnetic fields
Answer: D
Clarification: Electron Microscope uses electron beams and magnetic fields to produce the image, whereas the light microscope uses light waves and glass lenses. In electron microscopy, a much higher resolution is obtained with extremely short wavelength of the electron beam.

2. Electron Microscope can give a magnification up to ___________
A. 400,000X
B. 100,000X
C. 15000X
D. 100X
Answer: A
Clarification: The resolving power of the electron microscope is more than 100 times that of the light microscope, and it produces useful magnification up to 400,000X. It is possible to resolve objects as small as 10 Angstrom.

3. Which of the following are true for electron microscopy?
A. specimen should be thin and dry
B. image is obtained on a phosphorescent screen
C. electron beam must pass through evacuated chamber
D. specimen should be thin and dry, image is obtained on a phosphorescent screen and electron beam must pass through evacuated chamber
Answer: D
Clarification: Since electrons can travel only in high vacuum, the entire electron path through the instrument must be evacuated; specimens must be completely dehydrated prior to examination. Only very thin specimens can be observed in the conventional electron microscope since the penetrating power of electrons through matter is weak. The magnified image may be viewed on a phosphorescent or fluorescent screen.

4. Degree of scattering in transmission electron microscope is a function of __________
A. wavelength of electron beam used
B. number of atoms that lie in the electron path
C. number and mass of atoms that lie in the electron path
D. mass of atoms that lie in the electron path
Answer: C
Clarification: In a transmission electron microscope, contrast results from the differential scattering of electrons by the specimen, the degree of scattering being a function of the number and mass of atoms that lie in the electron path.

5. Negative Staining is used for examining _____________
A. virus particles
B. protein molecules
C. bacterial flagella
D. virus particles, protein molecules and bacterial flagella
Answer: D
Clarification: In negative-staining the electron opacity of the surrounding field is increased by using an electron-dense material such as phosphotungstic acid as a stain. Negative staining is particularly valuable for the examination of very small structures such as virus particles, protein molecules and bacterial flagella.

6. Which among the following helps us in getting a three-dimensional picture of the specimen?
A. Transmission Electron Microscope
B. Scanning Electron Microscope
C. Compound Microscope
D. Simple Microscope
Answer: B
Clarification: The scanning electron microscope lacks the resolving power obtainable with the transmission electron microscope but has the advantage of revealing a striking three-dimensional picture. The surface topography of a specimen can be revealed with clarity and depth of field not possible by any other method.

7. The secondary electrons radiated back in scanning microscope is collected by?
A. specimen
B. anode
C. vacuum chamber
D. cathode
Answer: B
Clarification: In scanning electron microscope (SEM), the surface of the specimen is irradiated with a very narrow beam of electrons. Such irradiations causes low energy (secondary) electrons to be ejected from the specimen which can then be collected on a positively-charged plate or anode thereby generating an electric signal.

8. On what factors do the intensity of secondary electrons depend upon?
A. shape of the irradiated object
B. chemical composition of the irradiated object
C. number of electrons ejected
D. size and chemical composition of the irradiated object, number of electrons ejected and on the number of electrons reabsorbed by surrounding
Answer: D
Clarification: The irradiations in SEM causes secondary electrons to be ejected from the specimen thereby generating a signal that is proportional to the number of electrons striking the anode. The intensity or the number of secondary electrons depends on the shape and the chemical composition of the irradiated object and also on the number of electrons ejected and the number of electrons reabsorbed by surrounding.

9. Where do we obtain the magnified image of the specimen in SEM?
A. cathode ray tube
B. phosphorescent screen
C. anode
D. scanning generator
Answer: A
Clarification: In TEM, the image is obtained on a phosphorescent screen but in SEM the magnified image of the surface topography of the specimen is obtained on the cathode ray tube. The electronic signals generated scan the specimen in a raster pattern in the manner of a television system to produce an image on a cathode ray tube.

10. Which of the following techniques are used in Transmission Electron Microscopy (TEM) for examining cellular structure?
A. Negative-Staining
B. Shadow Casting
C. Ultrathin Sectioning
D. Negative-Staining, Shadow Casting, Ultrathin Sectioning, Freeze-Etching
Answer: D
Clarification: Numerous techniques are available for use with electron microscopy which extends its usefulness in characterizing cellular structure. Some of them are Negative-Staining (which increases the electron opacity of surrounding), Shadow Casting (helps in producing three-dimensional structure of the object), Ultrathin Sectioning and Freeze-Etching.

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Microbiology Interview Questions and Answers for freshers focuses on “Energy Production by Anaerobic Processes”.

1. Glycolysis can occur in ___________
A. aerobic cells
B. anaerobic cells
C. both aerobic and anaerobic cells
D. neither aerobic and anaerobic cells
Answer: C
Clarification: Glycolysis does not require the presence of oxygen and therefore can occur in both aerobic and anaerobic cells. In anaerobic cells glucose is degraded into fermentation products and in aerobic cells glucose is degraded into carbon dioxide and water.

2. The step where glyceraldehyde-3-phosphate is oxidized is substrate-level phosphorylation.
A. True
B. False
Answer: B
Clarification: The step where glyceraldehyde-3-phosphate is oxidized to 1,3-Biphosphoglycerate is oxidative-level phosphorylation where a pair of electrons (two hydrogen atoms) is removed.

3. Xylulose-5-phosphate is an intermediate in ___________
A. Glycolysis
B. Pentose Phosphate Pathway
C. Entner-Doudoroff Pathway
D. Fermentation
Answer: B
Clarification: Epimerization of ribulose-6-phosphate yields xylulose-5-phosphate and ribulose-5-phosphate in Pentose-phosphate pathway. These two compounds are the starting point for a series of transketolase and transaldolase reactions.

4. How many molecules of glucose-6-phosphate are regenerated in pentose-phosphate pathway?
A. 3
B. 2
C. 5
D. 4
Answer: C
Clarification: From 6 molecules of ribulose-5-phosphate, 5 molecules of glucose-6-phosphate are again regenerated.

5. Entner-Doudoroff pathway takes place only in procaryotes.
A. True
B. False
Answer: A
Clarification: Entner-Doudoroff pathway is found both in aerobic and anaerobic procaryotes, particularly among Gram-negative bacteria but not in eukaryotes.

6. Which of the following are propionic acid bacteria?
A. Streptococcus
B. Acetobacter
C. Clostridium
D. Veillonella
Answer: D
Clarification: Veillonella is a propionic acid bacteria that produce propionic acid, acetic acid and carbon dioxide as fermentation products.

7. What is the other name of glycolysis?
A. PPP cycle
B. TCA cycle
C. C4 cycle
D. EMP pathway
Answer: D
Clarification: EMP is named after the scientists that proposed the pathway, and they are Embden, Meyerhof, Parnas. It involves the conversion of glucose into pyruvic acid.

8. How many ATPs are paid back during the Pentose phosphate Pathway?
A. 1
B. 3
C. 4
D. 5
Answer: A
Clarification: One ATP is paid back for converting glucose into glucose-6-phosphate in the presence of hexokinase enzyme.

9. Stickland reaction is the alternative name for ________
A. Lactic acid fermentation
B. Alcoholic fermentation
C. Mixed acid fermentation
D. Amino acid fermentation
Answer: D
Clarification: Amino acid fermentation reaction is also known as Stickland reaction alternatively.

To practice all areas of Microbiology for Interviews, .

Microbiology Multiple Choice Questions on “World of Bacteria II – Nonspore – Forming Gram – Positive Bacteria”.

1. Which of the following Nonspore forming Gram-positive rods show a negative result for catalase test?
A. Lactobacillus
B. Kurthia
C. Brocothrix
D. Renibacterium
Answer: A
Clarification: Lactobacillus which are strictly fermentative organisms show negative result for catalase test.

2. Which of the following is a characteristic of the genus Caryophanon?
A. anaerobic species
B. non-motile organism
C. disk-shaped cells
D. parasitic
Answer: C
Clarification: Caryophanon is unusual as it is composed of large, disk-shaped cells arranged in trichomes. They are aerobic organisms and are motile by peritrichous flagella.

3. Which of the following genus of organisms causes meningitis in adults?
A. Erysipelothrix
B. Listeria
C. Caryophanon
D. Brocothrix
Answer: B
Clarification: The species L.monocytogenes of the genus Listeria is a parasite and causes meningitis in adults and prenatal or postnatal disease in infants.

4. Brocothrix is a facultatively anaerobic genus of species.
A. True
B. False
Answer: A
Clarification: Brocothrix are rods often occurring in long, kinked filaments and are facultatively anaerobic.

5. Volutin granules stain which colour with dilute methylene blue?
A. Violet
B. Blue
C. Red
D. Reddish purple
Answer: D
Clarification: The cells of Corynebacterium accumulate intracellular volutin granules (metachromatic granules) which stain reddish purple with dilute methylene blue.

6. The cell walls of Corynebacterium contain mycolic acid containing ______________ carbon atoms.
A. 2 to 3
B. 100 to 150
C. 32 to 36
D. 20 to 25
Answer: C
Clarification: The cell walls of Corynebacterium contain mycolic acids (corynemycolic acids) containing 32 to 36 carbon atoms.

7. Cells of Arthrobacter in the stationary phase of growth are ____________ shaped.
A. rod
B. irregularly
C. coccoid
D. rudimentary branching
Answer: C
Clarification: Cells of Arthrobacter in the stationary phase of growth are distinctly coccoid; when these are inoculated into fresh media, they give rise to rod-shaped cells.

8. Which of the following genus of species occur on the surface of certain cheeses such as brick and Limburger?
A. Brevibacterium
B. Microbacterium
C. Cellulomonas
D. Arthrobacter
Answer: A
Clarification: B.linens of the Brevibacterium has its usual habitat on the surface of certain cheeses such as brick and Limburger, where it produces proteolytic enzymes that aid in the cheese-ripening process.

9. Which of the following genus of organisms are normal inhabitants of the human mouth?
A. Agromyces
B. Arachnia
C. Actinomyces
D. Rothia
Answer: D
Clarification: The genus Rothia is aerobic,catalase-positive, and a normal inhabitant of the human mouth.

10. Mycobacteria are acid-fast organisms.
A. True
B. False
Answer: A
Clarification: A major characteristic of mycobacteria is that they are acid-fast; that is, once stained with aniline dyes, they are difficult to decolourize, even when treated with a mixture of acid and alcohol.

11. The causative agent of leprosy is __________
A. M.intracellulare
B. M.leprae
C. M.kansasii
D. M.phlei
Answer: B
Clarification: Mycobacterium leprae is the causative agent of leprosy. They may be slightly curved or straight rods.

12. The walls of Nocardioforms contains the sugars ____________
A. sucrose and galactose
B. fructose and galactose
C. sucrose and arabinose
D. arabinose and galactose
Answer: D
Clarification: The walls of Nocardioforms contain the sugars arabinose and galactose. The peptidoglycan contains meso-diaminopimelic acid and no glycine interpeptide bridges occur between the peptidoglycan chains.

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