Category: MICROBIOLOGY Objective Questions

Microbiology Multiple Choice Questions on “Microorganisms Microscopic Examination – Light Microscope”.

1. Which part of the compound microscope helps in gathering and focusing light rays on the specimen to be viewed?
A. Eyepiece lens
B. Objective lens
C. Condenser lens
D. Magnifying lens
Answer: C
Clarification: Compound microscope contains three separate lens systems. The condenser lens is placed between the light source and the specimen and it gathers and focuses the light rays in the plane of the microscopic field to view the specimen.

2. What is the minimum distance for the eye to focus any object?
A. 11 cm
B. 25 cm
C. 32 cm
D. 4 2 cm
Answer: B
Clarification: The eye cannot focus on objects brought closer to it less than 25 cm; this is, accordingly the distance of maximal effective magnification. An object must also subtend an angle at the eye of 1 degree or greater.

3. Resolving power of a microscope is a function of ____________
A. Wavelength of light used
B. Numerical aperture of lens system
C. Refractive index
D. Wavelength of light used and numerical aperture of lens system
Answer: D
Clarification: The ability of a microscope to distinguish two adjacent points as distinct and separate is known as resolving power. Resolving power is a function of wavelength of light used and the numerical aperture (NA. of the lens system. NA refers to the refractive index of the medium multiplied with the sine value of the half-aperture angle.

4. The greatest resolution in light microscopy can be obtained with ___________
A. Longest wavelength of visible light used
B. An objective with minimum numerical aperture
C. Shortest wavelength of visible light used
D. Shortest wavelength of visible light used and an objective with the maximum numerical aperture
Answer: D
Clarification: The relationship between numerical aperture (NA. and resolution is:-
Resolution (D. = wavelength / 2(NA)
Thus maximum resolution is obtained with the shortest wavelength of visible light and an objective with the maximum NA.

5. Oil immersion objective lens has an NA value of____________
A. 0.65
B. 0.85
C. 1.33
D. 1.00
Answer: C
Clarification: NA = refractive index * sine (half-aperture angle).
The maximum NA for a dry objective is less than 1.0 as the refractive index of air is 1. The values of NA for oil immersion lens is slightly greater than 1.0 in the range of (1.2 to 1.4) as the refractive index of oil is 1.56.

6. In fluorescence microscopy, which of the following performs the function of removing all light except the blue light?
A. Exciter filter
B. Barrier filter
C. Dichroic mirror
D. Mercury arc lamp
Answer: A
Clarification: In fluorescence microscopy, the function of the exciter filter is to remove all but the blue light; the barrier filter blocks out blue light and allows any other light emitted by the fluorescing specimen to pass through and reach the eye.

7. Total Magnification is obtained by __________
A. Magnifying power of the objective lens
B. Magnifying power of eyepiece
C. Magnifying power of condenser lens
D. Magnifying power of both the objective lens and eyepiece
Answer: D
Clarification: The total magnification is determined by multiplying the magnifying power of the objective by that of the eyepiece. Generally, an eyepiece having a magnification of 10X is used although eyepieces of higher or lower magnifications are available.

8. In light microscopy, which of the following is used as fixatives prior to staining technique?
A. Osmic acid
B. Glutaraldehyde
C. Heat
D. Osmic acid, glutaraldehyde, heat
Answer: C
Clarification: Most staining techniques kill cells and so preliminary to staining, the cells are sometimes fixed. Commonly used chemical fixatives include osmic acid and mainly glutaraldehyde. But for light microscopy heat is the most commonly used fixative.

9. In Phase contrast microscopy, the rate at which light enters through objects is __________
A. Constant
B. Inversely proportional to their refractive indices
C. Directly proportional to their refractive indices
D. Exponentially related to their refractive indices
Answer: B
Clarification: Phase contrast microscopy is based on the fact that the rate at which light travels through objects is inversely related to their refractive indices. Since the frequency of light waves is independent of the medium through which they travel, the phase of a light ray passing through an object of the higher refractive index than the surrounding medium will be relatively retarded.

10. Which part of the light microscope controls the intensity of light entering the viewing area?
A. Coarse adjustment screw
B. Fine adjustment screw
C. Diaphragm
D. Condenser lens
Answer: C
Clarification: On the condenser is mounted a shutter like an apparatus called the diaphragm which opens and closes to permit more or less light into the viewing area. Condenser lens just helps in condensing the light rays. Coarse and fine adjustment screws are used for focusing under different power lens.

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Microbiology Multiple Choice Questions on “Energy Production – Some Principles of Bioenergetics”.

1. The respiratory chain of bacteria is associated with the _____________
A. mitochondrial membrane
B. cytoplasmic membrane
C. cell wall
D. cytoplasm
Answer: B
Clarification: The respiratory chain of bacteria is associated with the cytoplasmic membrane and that of eukaryotes is present in the mitochondrial membrane.

2. The prosthetic group of a cytochrome contains how many iron atoms?
A. one
B. two
C. three
D. four
Answer: A
Clarification: Cytochromes are a major class of oxidative enzymes whose prosthetic group is a derivative of heme and contains a single iron atom, which is responsible for the oxidative or reductive properties of the enzyme.

3. Among the following which can directly react with oxygen?
A. cytochrome c
B. cytochrome c₁
C. cytochrome a
D. cytochrome a₃
Answer: D
Clarification: Cytochrome a and a₃ together are called cytochrome oxidase, both of them contain copper. But only cytochrome a₃ can react directly with oxygen.

4. How many ATP molecules are formed for per molecule of FADH₂ reoxidized?
A. 3
B. 1
C. 2
D. 4
Answer: C
Clarification: Three ATP are formed per molecule of NADH₂ reoxidized but only two ATP molecules are formed per molecule of FADH₂ reoxidized, because of the high energy of NADH₂.

5. In aerobic respiration the terminal electron acceptor is oxygen, nitrate, sulfate, etc.
A. True
B. False
Answer: B
Clarification: In aerobic respiration the terminal electron acceptor is oxygen; in anaerobic respiration the final electron acceptor is nitrate, sulphate and carbonate.

6. In photosynthesis by green plants, algae, cyanobacteria which of the following acts as terminal electron acceptor?
A. Water
B. Oxygen
C. NADP+
D. FAD+
Answer: C
Clarification: In photosynthesis by green plants, algae and cyanobacteria, water serves as a primary electron donor and NADP+ as a terminal electron acceptor.

7. A reducing agent will accept electrons and an oxidizing agent will donate electrons.
A. True
B. False
Answer: B
Clarification: An oxidizing agent will absorb electrons and will therefore become reduced whereas a reducing agent donates electrons, becoming oxidized in the process.

8. K_eq is greater than 1.0 depending on which of the following conditions?
A. standard free energy change is negative
B. standard free energy change is positive
C. chemical reaction proceeds in reverse direction
D. products are not formed
Answer: A
Clarification: When standard free energy change is negative value then K_eq is greater than 1.0 and the formation of products is favoured.

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Microbiology test focuses on “World of Bacteria II – Endospore – Forming Gram – Positive Bacteria”.

1. Which of the following are mesophilic saprophytes?
A. B.polymyxa
B. B.anthracis
C. B.subtilis
D. B.thuringiensis
Answer: C
Clarification: Bacillus subtilis are mesophilic saprophytes and are widely distributed in nature. This means they can grow best within a temperature range of approximately 25 to 40 degrees Celsius.

2. Which of the following causes “milky disease” of Japanese beetle grubs?
A. B.thuringiensis
B. B.popilliae
C. B.sphaericus
D. B.anthracis
Answer: B
Clarification: B.popilliae is a pathogenic species of Bacillus species that causes “milky disease” of Japanese beetle grubs.

3. Which of the following species is associated with spoilage of canned goods?
A. B.stearothermophiles
B. B.cereus
C. B.subtilis
D. B.sphaericus
Answer: A
Clarification: B.stearothermophilus is a thermophilic species having a maximum of 65 to 75 degrees Celsius. The endospores are highly resistant to heat and, therefore, this species is one of those associated with spoilage of canned goods.

4. Which of the following genus of species play an active role in the decomposition of urea?
A. Bacillus
B. Sporosarcina
C. Clostridium
D. Desulfotomaculum
Answer: B
Clarification: Sporosarcinae are widely distributed in fertile soil, where they play an active role in the decomposition of urea.

5. C.perfringens is the major causative agent of __________________
A. botulism
B. tetanus
C. gas gangrene
D. anthrax
Answer: C
Clarification: Clostridium perfringens is the major causative agent of the wound infection known as gas gangrene.

6. Which of the following Clostridium species has the ability to fix Nitrogen?
A. C.difficile
B. C.pasteurianum
C. C.tetani
D. C.thermosaccharolyticum
Answer: B
Clarification: C.pasteurianum is a mesophilic soil clostridium that is particularly noted for its ability to fix Nitrogen.

7. The genus Desulfotomaculum obtain energy by anaerobic respiration.
A. True
B. False
Answer: A
Clarification: The members of the genus Desulfotomaculum obtain energy by anaerobic respiration, with sulphate serving as the terminal electron acceptor and organic substrates such as lactic or pyruvic acid serving as the electron donors.

8. Pseudomembranous colitis is a disease of _________________
A. stomach
B. wounds
C. bowel
D. limbs
Answer: C
Clarification: C.difficile causes pseudomembranous colitis, a severe disease of the bowel.

9. Bacillus species cannot fix Nitrogen.
A. True
B. False
Answer: B
Clarification: Bacillus polymyxa has the ability to fix Nitrogen under anaerobic conditions.

To practice all areas of Microbiology for tests, .

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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