Category: MICROBIOLOGY Objective Questions

Microbiology Multiple Choice Questions on “Microorganisms Control by Physical Agents – Fundamentals of Control”.

1. In which of the following situations will the logarithmic plot of survivors be constant?
A. physiological conditions are different
B. cells of microbial population vary in size
C. age and physiological conditions are uniform
D. temperature conditions are different
Answer: C
Clarification: Logarithmic plot reveals that the death rate is constant when all conditions are strictly uniform, including the age and the physiological condition of all the microorganisms in the population.

2. A suspension of E.coli exposed to heat treatment may yield a greater number of survivors if a plating medium of _____________ is used.
A. peptone
B. trypticase soy agar
C. deoxycholate agar
D. potato dextrose
Answer: B
Clarification: A suspension of E.coli exposed to heat treatment may yield a greater number of survivors if a plating medium of trypticase soy agar is used rather than a medium containing bile salts such as deoxycholate agar.

3. We require less time to kill the population of many cells.
A. True
B. False
Answer: B
Clarification: It takes time to kill the population and if we have many cells, we must treat them for a longer time to be reasonably sure that all of the bacteria are dead.

4. The effectiveness of heat in killing microorganisms is much greater in _____________
A. acid
B. alkali
C. neutral
D. acid and alkali
Answer: A
Clarification: The environment has a profound influence on the rate as well as the efficacy of microbial destruction. The effectiveness of heat is much greater in acid than in alkali material.

5. A high concentration of which of the following compounds in the material generally increases the thermal resistance of microorganisms?
A. proteins
B. carbohydrates
C. lipids
D. salts
Answer: B
Clarification: The consistency of the material will markedly influence the penetration of the agent and high concentration of carbohydrates generally increases the thermal resistance of organisms.

6. Which of the following show the maximum resistance to physical and chemical agents?
A. Viruses
B. Mold spores
C. Bacterial spores
D. E.coli
Answer: C
Clarification: In spore forming species, the bacterial spores are extremely resistant in comparison to growing vegetative cells to physical and chemical agents.

7. How much time is required by the young cells to be killed by a lethal agent?
A. 24 hours
B. 3-4 hours
C. 30 mins
D. 5 mins
Answer: C
Clarification: The young cells are all killed within 25 minutes but a considerable part of the more resistant, older cells still survives. Young, actively metabolizing cells are apt to be more easily destroyed than old, dormant cells.

8. Which of the following actions are not affected by antimicrobial agents?
A. cell wall synthesis
B. nucleic acid synthesis
C. protein synthesis
D. capsule formation
Answer: D
Clarification: Antimicrobial agents inhibit or kill microorganisms by any of these actions like damaging cell wall synthesis, inhibiting protein or nucleic acid synthesis and inhibition of enzyme action.

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Microbiology Multiple Choice Questions on “Wastewater and Treatment Processes”.

1. Which of the following sewerage systems carry domestic and industrial wastewater?
A. sanitary sewers
B. storm sewers
C. combined sewers
D. storm and combined sewers
Answer: A
Clarification: Sanitary sewers carry domestic and industrial wastewater for its ultimate treatment and disposal.

2. The more oxidizable organic material, the lesser the BOD.
A. True
B. False
Answer: B
Clarification: The magnitude of the BOD is related to the amount of organic material in the wastewater-i.e., the more oxidizable organic material, the higher the BOD.

3. Which of the following is a strict anaerobe?
A. Enterobacter
B. Alcaligenes
C. Pseudomonas
D. Methanosarcina
Answer: D
Clarification: Methane producers are strict anaerobes e.g., Methanobacterium, Methanosarcina, Methanococcus. They produce methane and carbon dioxide as end products.

4. In which of the following treatment involve oxidation of organic constituents of the wastewater?
A. Primary treatment
B. Secondary treatment
C. Advanced treatment
D. Final treatment
Answer: B
Clarification: Secondary or biological treatment is done to adsorb and ultimately oxidize organic constituents of the wastewater, i.e, to reduce the BOD.

5. The upper region of the trickling filter is favorable for the growth of _____________
A. fungi
B. protozoa
C. algae
D. bacteria
Answer: C
Clarification: The upper region of the trickling filter is favorable for the growth of algae, and at times their growth may become so extensive that it impairs the operation of the filter.

6. Activated sludge usually employs an aeration period of ________________
A. 1 hour
B. 24 hours
C. 10-15 hours
D. 4-8 hours
Answer: D
Clarification: The activated sludge process usually employs an aeration period of 4 to 8 hours, after which the mixture is piped to a sedimentation tank.

7. Oxidation ponds are very deep ponds.
A. True
B. False
Answer: B
Clarification: Oxidation ponds also called lagoons are shallow ponds which are 2 to 4 ft in depth designed to allow algal growth on the wastewater effluent.

8. Trickling filter is used in which of the following wastewater treatment processes?
A. Primary treatment
B. Secondary treatment
C. Advanced treatment
D. Final treatment
Answer: B
Clarification: The trickling filter is used in secondary treatment in which a stationary microbial culture is fed by a continuous supply of nutrients. It is used for filtration processes.

9. Belt filter presses are used in which of the following process?
A. Thickening
B. Stabilization
C. Dewatering
D. Disposal
Answer: C
Clarification: Dewatering is done by vacuum filters, belt filter presses and centrifuges and is often enhanced by the addition of polymer or other chemical coagulant aids.

10. Which of the following gases are produced in large amounts during sludge digestion?
A. methane
B. carbon-dioxide
C. hydrogen
D. nitrogen
Answer: A
Clarification: About 60-70% methane is produced during sludge digestion with smaller amounts of carbon dioxide, hydrogen and nitrogen.

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Microbiology Multiple Choice Questions on “Infection Process – Penetration of Epithelial Cell Layers”.

1. Which of the following microorganism causes infection in burns?
A. Pseudomonas aeruginosa
B. Clostridium perfringens
C. Borrelia sp
D. Streptococcus sp
Answer: A
Clarification: Burns often become infected by Pseudomonas aeruginosa or other aerobic or facultatively anaerobic bacteria from the surrounding.

2. V. cholerae does not penetrate into the body.
A. True
B. False
Answer: A
Clarification: V. cholerae, the causative agent of cholera, multiplies on the epithelial layer of the small intestine where it produces a toxin that causes the loss of fluid from the epithelial cells and kills the cells.

3. Which of the following microorganism causes relapsing fever in humans?
A. Pseudomonas aeruginosa
B. Clostridium perfringens
C. Borrelia sp.
D. Streptococcus sp.
Answer: C
Clarification: Borrelia sp. cause relapsing fever in humans when the spirochetes are introduced through the bite of a tick or a body louse.

4. Which of the following microorganism participates in active penetration into the body?
A. Clostridium perfringens
B. Shigella
C. Borrelia sp.
D. Pseudomonas aeruginosa
Answer: B
Clarification: In bacillary dysentery, Shigella bacteria penetrate into and kill the epithelial cells of the colon, then spread to adjacent cells, which are in turn killed.

5. Wounds and burns represent one active mechanism.
A. True
B. False
Answer: B
Clarification: Wounds and burns represent one passive mechanism and they can introduce pathogens directly into the underlying tissues.

6. Bacillary dysentery is caused by which of the following microorganism?
A. Clostridium perfringens
B. Borrelia sp.
C. Shigella
D. Pseudomonas aeruginosa
Answer: C
Clarification: Bacillary dysentery is caused by Shigella bacteria which penetrate into and kill the epithelial cells of the colon, then spread to adjacent cells, which are in turn killed.

7. In which of the following body part does the influenza virus does not penetrate?
A. small intestine
B. nasopharynx
C. trachea
D. bronchi
Answer: A
Clarification: The influenza virus penetrates the epithelial cells lining the nasopharynx, trachea and bronchi.

8. Which of the following is an arthropod?
A. Clostridium perfringens
B. Borrelia sp.
C. Shigella
D. Pseudomonas aeruginosa
Answer: B
Clarification: Arthropods follow passive penetration such as that by Borrelia species which causes relapsing fever in humans.

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Microbiology Multiple Choice Questions on “Morphology and Fine Bacteria – Structures Internal to the Cell Wall”.

1. Polyisoprenoid branched-chain lipids, are present in which of the following?
A. Archaebacteria
B. Eubacteria
C. Archaebacteria and Eubacteria
D. Cannot be determined
Answer: A
Clarification: In Archaebacteria, the lipids are polyisoprenoid branched-chain lipids, in which long-chain branched alcohols(phytanols) are ether linked to glycerol. In Eubacteria, the phospholipids are phosphoglycerides, in which straight-chain fatty acids are ester-linked to glycerol.

2. Cytoplasmic membrane and the cell material bounded by it plus the outer membrane of cell is known as _________
A. Protoplast
B. Cytoplast
C. Spheroplast
D. Cell membrane
Answer: C
Clarification: A protoplast is that portion of a bacterial cell consisting of the cytoplasmic membrane and the cell material bounded by it. When the cell has two membranes, the cytoplasmic membrane of the protoplast plus the outer membrane of the cell wall, the cell is called a spheroplast rather than protoplast.

3. Which among the following is associated with the export of exocellular enzymes?
A. central mesosomes
B. peripheral mesosomes
C. thylakoids
D. nucleus
Answer: B
Clarification: Peripheral mesosomes show only a shallow penetration into the cytoplasm, are not restricted to a central location, and are not associated with nuclear material and they are involved in the export of exocellular enzymes such as penicillinase.

4. Ribosomes of prokaryotes have a sedimentation coefficient of?
A. 90S
B. 80S
C. 50S
D. 70S
Answer: D
Clarification: Ribosomes of prokaryotes have a sedimentation coefficient of 70S and are composed of two subunits, a 50S and a 30S subunit. But the ribosomes of eukaryotes have a sedimentation coefficient of 80S and are composed of a 60S and a 40S subunit.

5. Poly-beta-hydroxybutyrate(PHB. present in aerobic bacteria can serve as?
A. a reserve carbon and energy source
B. a reserve source of phosphate
C. acceptor of oxygen
D. provides buoyancy
Answer: A
Clarification: A polymer found in aerobic bacteria, especially under high-carbon,low-nitrogen culture conditions, is a chlorofoam-soluble, lipid like material, poly-beta-hydroxybutyrate(PHB), which can serve as a reserve carbon and energy source.

6. Which among the following compound when added to cytoplasmic membrane helps in maintaining the rigidity of cell?
A. lipopolysaccharide
B. hopanoid
C. phosphoglycerides
D. amino acids
Answer: B
Clarification: Hopanoids are hydrophobic chemical compounds which when added to the cytoplasmic membrane forms a stable and hard compound that helps in maintaining the rigidity of cell.

7. The nucleoid can be made visible under the light microscope by _________
A. Methylene blue
B. Iodine
C. Nile blue
D. Feulgen staining
Answer: D
Clarification: Bacteria consist of nucleotide, consisting of a single, circular DNA molecule in which all the genes are linked and it is not a discrete nucleus. The nucleoid can be made visible under the light microscope by Feulgen staining,which is specific for DNA.

8. What helps in the heat resistance of the endospore?
A. calcium-DPA complex
B. water
C. methylene
D. calcium
Answer: A
Clarification: All endospores contain large amounts of dipicolinic acid (DPA). It occurs in combination with large amounts of calcium and is probably located in the central part of the spore. The calcium-DPA complex plays a role in the heat resistance of endospores.

9. Cysts also have high heat resistance like endospores.
A. True
B. False
Answer: B
Clarification: Cysts are dormant, thick-walled, desiccation-resistant forms that develop by differentiation of a vegetative cell and which can later germinate under suitable conditions. In some ways cysts resemble endospores but they do not have the high heat resistance of endospores.

10. Which of the following methods can be utilized for removing peripheral proteins of the cytoplasmic membrane?
A. treatment by detergents
B. osmotic shock
C. heat application
D. destruction of the membrane
Answer: B
Clarification: Peripheral proteins are loosely attached to cytoplasmic membrane and can be removed by mild treatments such as osmotic shock. On the other hand, integral proteins can be removed only by the destruction of the membrane, as with treatment by detergents.

11. Which of the following are true for cytoplasmic membrane?
A. hydrophilic barrier
B. hydrophobic barrier
C. site of generation of protonmotive force
D. hydrophobic barrier and site of generation of protonmotive force
Answer: D
Clarification: The cytoplasmic membrane is a hydrophobic barrier to penetration by most water-soluble molecules. Because of its impermeability to protons, the cytoplasmic membrane is the site of the generation of the proton motive force.

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Microbiology Multiple Choice Questions on “Microbial Metabolism – Biosynthesis of Deoxyribonucleic Acid”.

1. In DNA molecule, the amount of purines is equal to the amount of pyrimidines.
A. True
B. False
Answer: A
Clarification: In DNA the nitrogenous bases like adenine binds with thymine, and guanine binds with cytosine. As a consequence, the ratio of adenine to thymine or of guanine to cytosine in double stranded DNA is always 1:1. So the amount of purines is equal to the amount of pyrimidines.

2. RNA consists of which combination of bases?
A. Thymine, Guanine, Cytosine
B. Guanine, Cytosine, Uracil
C. Thymine, Adenine, Guanine
D. Adenine, Cytosine, Thymine
Answer: B
Clarification: RNA is composed of nitrogenous bases adenine, guanine, cytosine and uracil. They do not contain thymine as present in DNA.

3. Which of the following are features of semiconservative replication?
A. RNA replicates DNA molecule
B. The DNA molecule produced contains two old templates
C. One new DNA helix is formed
D. DNA duplicates itself and the new chain contains old template strand and new complementary strand
Answer: D
Clarification: In semiconservative replication DNA duplication occurs in which one polynucleotide chain acts as a template to direct the synthesis of a new chain complementary to itself. It results in two daughter helices, each containing one old template strand and one new complementary strand.

4. The chromosome of a typical bacterium is ________________
A. circular double-stranded DNA
B. circular single-stranded DNA
C. double-helix DNA
D. single stranded DNA
Answer: A
Clarification: The chromosome of a typical bacterium is a circular double-stranded DNA molecule; that is, the double helix for a complete genome has no free ends.

5. If the chromosome were extended linearly then it would approximately measure?
A. 13500 micrometre
B. 1000 micrometre
C. 1250 micrometre
D. 500 micrometre
Answer: C
Clarification: If the chromosome were extended linearly then it would measure approximately 1250 micrometers or 1.25 mm which is several hundred times longer than the bacterial cell that contains it.

6. The Lambda Bacteriophage carries out which of the following replication methods?
A. Theta mode
B. Sigma mode
C. Linear mode
D. Does not carry out replication
Answer: B
Clarification: The Lambda Bacteriophage follows sigma mode of replication in which the intermediate structures of DNA have sigma conformation. In this replication begins with the cleavage of a phosphodiester bond in one strand of the circular DNA molecule to produce a nick with 3’-OH and 5’-PO4 ends on that strand.

7. Which of the following replication methods leads to the production of two circular daughter chromosomes?
A. Theta mode
B. Sigma mode
C. Linear mode
D. Rolling circle method
Answer: A
Clarification: In Theta mode of replication a circular parental chromosome is replicated to two circular daughter chromosomes, in each of which one strand of the parental DNA molecule is conserved and a complementary strand is newly synthesized.

8. Eukaryotes replicate their DNA from one origin or growing point per molecule.
A. True
B. False
Answer: B
Clarification: Procaryotes replicate their DNA from one origin or growing point per molecule while eukaryotes replicate from many origins per molecule. Replication may occur in either a unidirectional or bidirectional manner from each origin.

9. DNA gyrase is a ______________ protein.
A. helix-unwinding
B. helix-destabilizing
C. helix-relaxing
D. helix-winding
Answer: C
Clarification: DNA gyrase is a helix-relaxing protein which works along with other enzymes and participates in opening the parental DNA helix ahead of the replication fork.

10. Which of the following enzyme removes the RNA primer with its 5’-nuclease activity?
A. DNA polymerase I
B. DNA polymerase II
C. DNA polymerase III
D. RNA polymerase
Answer: A
Clarification: DNA polymerase I remove the RNA primer with its 5”-nuclease activity; simultaneously it fills in the gap with DNA via its 3’-polymerase activity.

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Microbiology Multiple Choice Questions on “Some Fungi of Special Interest”.

1. Which fungi causes black wart disease of potato?
A. Saprolegnia parasitica
B. Synchytrium endobioticum
C. Rhizopus stolonifer
D. Saccharomyces cerevisiae
Answer: B
Clarification: Synchytrium endobioticum is the most serious parasite of the class Chytridiomycetes that causes black wart disease of potato. The dark warts on the potatoes are galls in which the host cells have been stimulated to divide by the fungus.

2. Zygomycetes have which type of mycelia?
A. nonseptate
B. septate with uninucleate
C. septate with multi muclei
D. white,nonseptate
Answer: D
Clarification: Morphologically, the mycelia of Zygomycetes are usually white or gray and are nonseptate.

3. In the life cycle of Rhizopus stolonifer,when the protoplasts and nuclei of both gametangia coalesce, the structure is known as ________________
A. progametangia
B. coenozygote
C. zygospore
D. zygote
Answer: B
Clarification: The walls between two gametangia dissolve and their protoplasts coalesce. Nuclei of both mating types fuse in pairs, producing many zygote nuclei. The structure that contains them is then called a coenozygote.

4. Schizosaccharomyces versatilis is isolated from ________________
A. grape juice
B. cheese
C. honey
D. beer
Answer: A
Clarification: Schizosaccharomyces versatilis is isolated from grape juice. It grows like yeast but it can also form a true mycelium.

5. Legitimate copulation refers to ___________________
A. fusion between cells of same mating type
B. fusion between cells of different mating type
C. no fusion
D. different sex cells are present within the same body
Answer: B
Clarification: Fusion normally occurs only between cells of difffering mating types, a process termed as legitimate copulation. Such fusions result in diploid cells which form asci containing viable ascospores.

6. Neurospora sp. is important for the study of _____________________
A. human diseases
B. antibiotics
C. genetics and metabolic pathway
D. plant diseases
Answer: C
Clarification: Neurospora sp. which belongs to the class Ascomycetes is of particular interest to biologists because of its wide use in the study of genetics and metabolic pathways. Some species are also responsible for food spoilage and some are used in industrial fermentation.

7. Cryptococcosis is a disease of ________________
A. bacterial infection
B. parasitic infection
C. viral infection
D. mycotic infection
Answer: D
Clarification: Cryptococcus neoformans is an important basidiomycetous pathogen of humans, causing cryptococcosis, a generalized mycotic infection involving the bloodstream as well as lungs, central nervous system and other organs.

8. Aspergillus niger is used in the production of _______________
A. cheese
B. citric acid
C. gluconic acid
D. citric acid and gluconic acid
Answer: D
Clarification: It is an economically important fungi because they are used in a number of industrial fermentations, including the production of citric acid and gluconic acid in abundance.

9. Endocarditis is caused by which of the following fungi?
A. Candida albicans
B. Penicillium notatum
C. Penicillium chrysogenum
D. Agaricus campestris
Answer: A
Clarification: Candida albicans is often isolated from warm-blooded animals, including humans and becomes pathogenic and causes many serious infections. Endocarditis is caused by this organism and it is an infection of the heart.

10. What do you mean by hypertrophy?
A. repeated cell division
B. infection by zoospore
C. increase in cell volume
D. decrease in cell volume
Answer: C
Clarification: In the wart disease of potato, when the host cell is infected by a zoospore, it reacts by undergoing hypertrophy,i.e., an increase in cell volume, and adjacent cells also enlarge to form the characteristic rosette.

11. Which of the following fungi causes severe epidemic of disease among fish in the natural environment?
A. Saprolegnia ferax
B. Saprolegnia parasitica
C. Neurospora crassa
D. Neurospora sitophila
Answer: B
Clarification: Species of Saprolegnia are common in soil and fresh water; hence they are commonly called water molds. S.parasitica causes severe epidemics of disease among fish in the natural environment.

12. Reproductive organs are formed on the rhizoidal hyphae.
A. True
B. False
Answer: B
Clarification: The rhizoidal hyphae enter the substratum and serve to anchor the organism and to absorb nutrients, and the branched hyphae is the one on which reproductive organs are formed.

13. Rhizopus produces clusters of rootlike holdfasts called _____________
A. stolons
B. hyphae
C. runners
D. rhizoids
Answer: D
Clarification: The molds produce clusters of rootlike holdfasts called rhizoids. They also produce stolons or runners capable of taking root where that may give rise to new organisms.

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