Category: MICROBIOLOGY Objective Questions

Microbiology Multiple Choice Questions on “Bacteria Cultivation – Nutritional Requirements”.

1. The organisms which can use reduced inorganic compounds as electron donors are known as _________
A. chemotrophs
B. organotrophs
C. lithotrophs
D. phototrophs
Answer: C
Clarification: Organisms that can use reduced inorganic compounds as electron donors are termed as lithotrophs. Some organisms which use organic compounds as electron donors are called organotrophs.

2. Which of the following is the nutritional characterization of Escherichia coli?
A. Chemotrophic
B. Organotrophic
C. Autotrophic
D. Chemotrophic, Organotrophic, Heterotrophic
Answer: D
Clarification: Escherichia coli are chemotrophic, organotrophic, and heterotrophic organisms. This means they rely on chemical compounds for their energy and uses organic compounds as electron donors. They also require organic compounds as their carbon source and are hence heterotrophic.

3. Which of the following amino acids require sulphur for their synthesis?
A. tryptophan
B. methionine
C. cystine
D. methionine and cystine
Answer: D
Clarification: Sulphur is needed for synthesis of certain amino acids like methionine and cystine. Some bacteria require organic sulphur compounds, some are capable of utilizing inorganic sulphur compounds and some can even use elemental sulphur.

4. Phosphorus is essential component of __________
A. teichoic acid
B. nucleotides
C. phospholipids
D. teichoic acid, nucleotides, phospholipids
Answer: D
Clarification: Phosphorus, usually supplied in the form of phosphate, is an essential component of nucleotides, nucleic acids, phospholipids, teichoic acids, and other components.

5. Which of the following are trace elements?
A. Potassium ion
B. Sodium ion
C. Copper ion
D. Magnesium ion
Answer: C
Clarification: Trace elements are those elements that are needed at very low concentrations such as Zinc ion, Copper ion, Manganese ion, Nickel ion, Cobalt ion, Boron ion, Molybdenum ion. They always occur as contaminants of other components of culture media in amounts sufficient to support bacterial growth.

6. Which of the following ions are cofactors for various enzymes?
A. Potassium ion
B. Iron ion
C. Magnesium ion and Iron ion
D. Calcium ion
Answer: C
Clarification: Among the trace elements, iron ion, magnesium ion, zinc ion, manganese ion and copper ion are known to be cofactors for various enzymes.

7. ”Red extreme halophiles”, are members of the archaebacterial which cannot grow with less than 12 to 15 percent NaCl.
A. True
B. False
Answer: A
Clarification: Most bacteria do not require Na ion, but certain marine bacteria, cyanobacteria and photosynthetic bacteria do require it. For those members of the archaeobacteria known as the “red extreme halophiles”, the requirement is astonishing: they cannot grow with less than 12 to 15 percent NaCl. They require this high level of NaCl for maintenance of the integrity of their cell walls and for the stability and activity of certain of their enzymes.

8. Which of the following are functions of water in the culture medium?
A. nutrients must be in aqueous solution
B. cofactor of enzymes
C. provides resistance to sudden transient temperature changes
D. it is a chemical reactant, nutrients must also be present in aqueous solution and provide resistance to sudden temperature changes
Answer:d
Clarification: In the case of bacteria, all nutrients must be in aqueous solution before they can enter the cells. The high specific heat of water provides resistance to sudden, transient temperature changes in the environment. Water is also a chemical reactant, being required for the many hydrolytic reactions carried out by a cell.

9. Chromatium okenii uses which of the following compound as electron donor?
A. Hydrogen sulphide
B. Fatty acids
C. Alcohol
D. Succinate
Answer: A
Clarification: Chromatium okenii are photolithotrophs i.e., they are phototrophic bacteria that uses inorganic compounds as their source of electrons. They use Hydrogen Sulphide as its electron donor, oxidizing it to elemental sulphur.

10. Which of the following bacteria can grow both as chemolithotrophs or as chemoorganotrophs?
A. Nitrosomonas sp.
B. Pseudomonas pseudoflava
C. Rhodospirillum rubrum
D. Chromatium okenii
Answer: B
Clarification: Pseudomonas pseudoflava can grow either as chemolithotrophs or chemoorganotrophs. They can use either the organic compound glucose or the inorganic compound hydrogen as its source of electrons.

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Microbiology Multiple Choice Questions on “Microbial Metabolism – Transcription and Translation of Genetic Information”.

1. Translation takes place before transcription.
A. True
B. False
Answer: B
Clarification: According to the central dogma of molecular genetics, the first step is DNA replication, the second is a transcription and the last step is translation.

2. Which of the following bacteria can synthesize all of the amino acids required for protein synthesis?
A. E.coli
B. Lactobacillus bravis
C. Saccharomyces cerevisiae
D. Bacillus subtilis
Answer: A
Clarification: Microorganisms differ widely in their ability to synthesize amino acids like E.coli can synthesize all of the amino acids required for protein synthesis, whereas lactic acid bacteria cannot.

3. RNAase is a single polypeptide chain of __________ amino acid residues.
A. 2
B. 350
C. 4
D. 124
Answer: D
Clarification: RNAase is a single polypeptide chain of 124 amino acid residues; it is folded, bent and twisted into a globular shape in its active form.

4. Protein synthesis in bacteria takes place on which of the following organelles?
A. Endoplasmic Reticulum
B. Golgi body
C. Ribosomes
D. Mitochondria
Answer: C
Clarification: Protein synthesis in bacteria takes place on the ribosomes, which are larger RNA-protein particles in the cytoplasm of the bacterial cell.

5. Which of the following RNA constitutes 90 percent of the total cellular RNA?
A. rRNA
B. tRNA
C. mRNA
D. hnRNA
Answer: A
Clarification: Ribosomal RNA (rRNA. constitutes about 90 percent of the total cellular RNA and this is important from all other types of RNA.

6. The synthesis of polynucleotide chain of mRNA is catalyzed by the enzyme _____________
A. RNA helicase
B. RNA polymerase
C. DNA polymerase
D. DNA helicase
Answer: B
Clarification: The synthesis of polynucleotide chain of mRNA is catalyzed by the enzyme RNA polymerase. The process in which a single-stranded mRNA is synthesized complementary to one DNA strand is called transcription.

7. Which of the following is responsible for the initiation of RNA polymerase activity?
A. initiation site
B. promoter region
C. sigma factor
D. rho factor
Answer: C
Clarification: In bacteria, the initiation of RNA polymerase activity at the initiation site is due to an initiation factor called the sigma factor, which is a component of the enzyme.

8. Rho factor is a dimeric protein factor.
A. True
B. False
Answer: B
Clarification: Rho factor is a tetrameric protein factor that binds to RNA polymerase and promotes its termination. When transcription has been completed, rho dissociates from the RNA polymerase-DNA complex.

9. The following code codes for which of the amino acid respectively?
AUG and GUG
A. Phenylalanine, tyrosine
B. Methionine, valine
C. Methionine, alanine
D. Lysine, valine
Answer: B
Clarification: Three base triplets form a codon that codes for an amino acid. Thus AUG codes for methionine and GUG codes for Valine. AUG and GUG are both initiating codons for translation.

10. Which of the following are non-sense codons?
A. AUG
B. GUG
C. UAA
D. UCU
Answer: C
Clarification: UAA, UAG and UGA are polypeptide-chain-terminating codons and are called non-sense codons.

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Microbiology Multiple Choice Questions on “Algae Biological and Economic Importance”.

1. Alginic acid is obtained from ______________
A. brown algae
B. red algae
C. yello-green algae
D. golden algae
Answer: A
Clarification: Alginic acid and its salts are obtained from the walls of brown algae, where they may represent as much as 25 percent of the dry weight. Laminaria, Fucus are some of the species producing this compound.

2. Agar is obtained from the algal species of _______________
A. Chondrus
B. Gigartina
C. Gelidium
D. Laminaria
Answer: C
Clarification: Species of Gelidium and Gracilaria belonging to red algae are extensively used for obtaining agar.

3. Carrageenan is used as a ______________
A. emulsifier
B. solidifying agent
C. binder
D. emulsifier and binder
Answer: D
Clarification: Carrageenan has been used as a stabilizer or emulsifier in foods such as ice-cream and other milk products. It is also used as a binder in toothpaste or in pharmaceutical products, as well as an agent in ulcer therapy.

4. The famous Japanese dish sushi is made with the help of the red algae named ____________
A. Nemalion
B. Porphyra
C. Chondrus
D. Eucheuma
Answer: B
Clarification: Porphyra is used as a food in Japan, where it is called “nori” and is usually processed into dried sheets. Nori is commonly toasted over a flame and sprinkled in soup or rice, or it is rolled around flavoured rice with fish or vegetables to make sushi.

5. Which among the following is a pathogenic algae for humans?
A. Prototheca
B. Chlorella
C. Cephaleuros
D. Acanthopeltis
Answer:a
Clarification: Prototheca has been found to be a probable pathogen of humans. It has been found in systemic and subcutaneous infections, as well as in bursitis.

6. Algae are known as primary producers.
A. True
B. False
Answer: A
Clarification: Algae form the base or beginning of most aquatic food chains because of their photosynthetic activities and are therefore called primary producers of organic matter.

7. Agar and carrageenan are polymers of _________________
A. glucose
B. phosphoric acid
C. starch
D. galactose
Answer: D
Clarification: Agar and carrageenan are polymers of galactose, or galactose-containing compounds, with sulfated groups. Agar and carrageenan are both called sulfated galactans.

8. Which of the following species are important for cervical dilation?
A. Laminaria japonica
B. Gracilaria
C. Chondrus
D. Gonyaulax catenella
Answer: A
Clarification: The stipe of the brown alga Laminaria japonica may be used by the physicians for cervical dilation and/or softening of the cervix (for example, in performing an abortion or placing a radium implant).

9. Which of the following algae continues to be a significant food in China?
A. brown algae
B. green algae
C. red algae
D. yellow algae
Answer: C
Clarification: Red algae continue to be significant food in China. Such algae have been a food staple and delicacy for the Chinese for thousands of years.

10. Which of the following species produces neurotoxin which causes the death of aquatic animals?
A. Chlorella
B. Gonyaulax
C. Prototheca
D. Cephaleuros
Answer: B
Clarification: It is known that certain dinoflagellates belonging to the genera Gymnodinium and Gonyaulax cause death of aquatic animals by producing a high molecular weight neurotoxin.

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Microbiology Multiple Choice Questions on “Characteristics and Definition of Chemical Agents”.

1. A chemical agent that kills the microorganisms and is commonly applied to substances used on inanimate objects are _______________
A. Antiseptics
B. Sanitizer
C. Disinfectants
D. Antibiotics
Answer: C
Clarification: Disinfectant is a chemical agent that kills the growing forms but not necessarily the resistant spore forms of disease-producing microorganisms. They are commonly applied to substances used on inanimate objects.

2. An agent that prevents the growth of bacteria are known as __________________
A. Bactericide
B. Bacteriostatic
C. Antimicrobial
D. Antibiotic
Answer: B
Clarification: An agent that prevents or inhibits the growth of bacteria are known as bacteriostatic agents and the condition is known as bacteriostasis.

3. For using any chemical agent, we need to increase the temperature of the environment.
A. True
B. False
Answer: B
Clarification: One of the characteristics of chemical agents is that they should be toxic to microorganisms at room or body temperature. In using the compound, it should not be necessary to raise the temperature beyond that normally found in the environment where it is to be used.

4. Which of the following is the characteristics of a sanitizer?
A. destroys all microbial forms
B. prevents the growth or action of microorganisms
C. reduces the microbial population to safe levels
D. kills all the bacteria and the bacterial spores
Answer: C
Clarification: Sanitizer is an agent that reduces the microbial population to safe levels as prescribed by public health requirements. Usually it is a chemical agent that kills 99.9% of the growing bacteria and are generally applied to inanimate objects.

5. Which of the following is not a chemical agent for microbial control?
A. Radiations
B. Antibiotics
C. Antiseptics
D. Germicide
Answer: A
Clarification: Radiations are physical agents for microbial control and include ionizing as well as non-ionizing radiations to kill the microorganisms.

6. Escherichia coli is much more resistant to cationic disinfectants than Staphylococcus aureus.
A. True
B. False
Answer: A
Clarification: Chemical agents are not all equally effective against bacteria, fungi, and other microorganisms. Differences exist between Gram-positive and Gram-negative bacteria:
Escherichia coli is much more resistant to cationic disinfectants than Staphylococcus aureus.

7. The process of killing all microorganisms along with their spores is ____________________
A. Disinfection
B. Antisepsis
C. Sanitization
D. Sterilization
Answer: D
Clarification: Sterilization is the process of destroying all forms of microbial life. The term sterilization refers to the complete absence or destruction of all microorganisms and should not be used in a relative sense.

8. Which of the following are generally applied on living animal tissues?
A. Antiseptics
B. Disinfectants
C. Preservatives
D. Sanitizer
Answer: A
Clarification: Antiseptics are substances that opposes sepsis,i.e., prevents the growth or action of microorganisms either by destroying microorganisms or by inhibiting their growth and metabolism. They are usually applied on living animal tissues.

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Microbiology Multiple Choice Questions on “Preservation of Foods”.

1. The temperatures used for canning foods ranges from ____________________
A. 0-20 degree C
B. 20-60 degree C
C. 60-100 degree C
D. 100-121 degree C
Answer: D
Clarification: The temperatures used for canning foods ranging from 100 degrees C for high-acid foods to 121 degrees C for low-acid foods.

2. In the high-temperature short-time (HTST) method of pasteurization, milk is exposed to a temperature of _________
A. 132 degree F
B. 145 degree F
C. 161 degree F
D. 120 degree F
Answer: C
Clarification: The HTST process employs equipment capable of exposing milk to a temperature of 161 degrees F (71.7 degrees C. for 15 secs.

3. Sterilization occurs at high temperatures for long periods of time.
A. True
B. False
Answer: B
Clarification: Sterilization exposes milk to ultrahigh temperatures for very short periods of time, for example, 300 degrees F (148.9 degrees C. for 1 to 2 seconds.

4. Which of the following microorganism survive at -9 to -17 degree C?
A. Salmonella
B. Staphylococci
C. Bacilli
D. Clostridium
Answer: A
Clarification: Species of Salmonella survive for longer periods of time at -9 to -17 degree C which is unlike the situation in which microbial count of most frozen foods decreases during storage.

5. Which of the following microorganism is eliminated in canned foods?
A. Mycobacterium tuberculosis
B. Coxiella burnetii
C. Clostridium botulinum
D. Lactobacillus
Answer: C
Clarification: The most important organism to be eliminated in canned foods is the spore forming anaerobe Clostridium botulinum, which is capable of producing a very potent lethal toxin.

6. Phosphatase enzyme present in milk is destroyed in which of the following processes?
A. Sterilization
B. Canning
C. Dehydration
D. Pasteurization
Answer: D
Clarification: Phosphatase is an enzyme present in raw milk and in many tissues which are destroyed by adequate pasteurization.

7. Jellies and jams are rarely affected by bacterial action.
A. True
B. False
Answer: A
Clarification: Jellies and jams are rarely affected by bacterial action because of high sugar content. However it is uncommon to find mold growth on the surface of jelly which has been exposed to air.

8. Which chemical is used to inhibit mold growth in bread?
A. benzoic acid
B. nitrates
C. sorbic acid
D. lactic acid
Answer: C
Clarification: Sorbic acid and propionic acid are used to inhibit mold growth in bread. They are organic in nature.

9. Acetic acid and lactic acid are used for __________________
A. curing meats
B. preservation of color
C. preservation of pickles
D. inhibiting mold growth
Answer: C
Clarification: Foods prepared from fermentation processes,e.g., sauerkraut, pickles, and silage for animals are preserved mainly by acetic, lactic and propionic acids produced during the microbial fermentation.

10. Which of the following method is used for treatment of water used for the depuration of shellfish?
A. Chemicals
B. Radiation
C. Low temperature
D. Osmotic pressure
Answer: B
Clarification: Radiations are used in the food industry, control of surface growth on bakery products, sanitation of equipment and treatment of water used for the depuration (cleansing) of shellfish.

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Microbiology Multiple Choice Questions on “Microbial Virulence Factors”.

1. Which bacteria has an unusual capsule among the following?
A. Haemophilus influenzae
B. Klebsiella pneumoniae
C. Streptococcus pneumoniae
D. Bacillus anthracis
Answer: D
Clarification: The capsule of B. anthracis is unusual in that it is composed of a polypeptide rather than a polysaccharide.

2. For Clostridium botulinum type A toxin, 1 MLD for a mouse is ____________
A. 2.5 X 10^-5 µg
B. 4 X 10^-5 µg
C. 6 X 10^-2 µg
D. 5 µg
Answer: A
Clarification: Clostridium botulinum type A produces the most potent toxin known: 1 MLD for a mouse is 2.5 X 10^-5 µg of the purified toxin.

3. What is the chemical nature of endotoxins?
A. protein
B. polysaccharide
C. lipopolysaccharide
D. lipid
Answer: C
Clarification: Endotoxins are lipopolysaccharide in nature and are released from cell walls of lysed Gram-negative bacteria.

4. Exotoxins are heat-labile in nature.
A. True
B. False
Answer: A
Clarification: Exotoxins are heat-labile in nature and are inactivated easily by boiling which is not the case with endotoxins.

5. Which type of toxin is tetanus toxin?
A. enterotoxin
B. neurotoxin
C. cytotoxin
D. endotoxin
Answer: B
Clarification: Tetanus toxins affect nerve tissues and are hence termed as neurotoxins. It comes under the broad category of exotoxins.

6. Which of the following is a plasmid-mediated toxin?
A. diphtheria toxin
B. botulism toxin
C. tetanus toxin
D. food-poisoning toxin
Answer: D
Clarification: Plasmid-mediated toxin is the enterotoxin made by food-poisoning strains of S.aureus. Plasmid carries the gene for the toxin.

7. The B region of diphtheria toxin has the enzymatic activity.
A. True
B. False
Answer: B
Clarification: By means of the B region the toxin binds to the membrane of a tissue cell. The A region consists of the enzymatic activity and catalyzes the reaction that inactivates elongation factor 2 (EF-2), a factor essential for elongation of polypeptide chain during protein synthesis.

8. Which amino acid is an inhibitory transmitter?
A. alanine
B. tyrosine
C. glycine
D. phenylalanine
Answer: C
Clarification: To render neurons temporarily insensitive to stimulation, it is accomplished in the central nervous system by the action of a chemical called an inhibitory transmitter, viz., the amino acid glycine.

9. Which toxin causes paralysis of muscles?
A. Diphtheria toxin
B. Botulinum toxin
C. Tetanus toxin
D. Cholera toxin
Answer: B
Clarification: The botulinum toxin binds to the axon near the neuromuscular junction and prevents the secretion of acetylcholine; thus the muscle cannot contract and paralysis occurs.

10. How many B subunits are present in cholera toxin?
A. 1
B. 2
C. 3
D. 5
Answer: D
Clarification: Cholera toxin consists of one A subunit and five B subunits. The B subunits are responsible for attachment of the toxin to the surface of the epithelial cells of the small intestine.

11. Which of the following statement is wrong regarding the effects of cholera toxin?
A. loss of fluid from the body
B. pH of blood remains constant
C. hemoconcentration
D. bicarbonate ions are lost from blood
Answer: B
Clarification: Since bicarbonate ions are lost from the blood, the pH of the blood falls, which may lead to death by acidosis.

12. Which of the following toxin is a hemolysin?
A. diphtheria toxin
B. botulism toxin
C. tetanus toxin
D. streptolysin O
Answer: D
Clarification: Streptolysin O (SLO) is a hemolysin, causing beta hemolysis around the colonies on blood-agar plates incubated anaerobically. It also acts as a leukocidin.

13. Hylauronidase enzyme is produced by which of the following organism?
A. C. perfringens
B. S. pyogenes
C. S. aureus
D. Mycoplasma
Answer: A
Clarification: Hylauronidase enzyme is produced by the gas gangrene causing organism C. perfringens and has been thought to enhance penetration of the host tissues by hydrolyzing hyaluronic acid.

14. Which of the following has the ability to bind antibodies?
A. Coagulase
B. Streptokinase
C. Protein A
D. Hydrogen Peroxide
Answer: C
Clarification: Protein A is located on the cell wall of S. aureus and has the ability to bind antibodies, regardless of their specificity. The antibody molecules are distorted and their binding site is exposed.

15. LT toxin is produced by _____________
A. S. aureus
B. E.coli
C. B. anthracis
D. C. perfringens
Answer: B
Clarification: LT toxin is produced by E.coli and it is an enterotoxin, causing diarrhea. The mechanism is similar to that of cholera toxin.

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