Category: MICROBIOLOGY Objective Questions

Microbiology Multiple Choice Questions on “Microorganisms Microscopic Examination – Microbial Stains”.

1. The dye eosinate of methylene blue belongs to which group?
A. Acidic dye
B. Basic dye
C. Neutral dye
D. Oxazine dye
Answer: C
Clarification: A neutral dye is a complex salt of a dye acid with a dye base so eosinate of methylene blue is an example of a neutral dye. An acidic dye is one in which the charge on the dye ion is negative and a basic dye is one in which the charge carried by the dye ion is positive.

2. What is the correct order of staining reagents in Gram-Staining?
A. Crystal violet, alcohol, iodine solution, safranin
B. Crystal violet, iodine solution, alcohol, safranin
C. Crystal violet, safranin, alcohol, iodine solution
D. Iodine solution, crystal violet, alcohol, safranin
Answer: B
Clarification: Gram staining is a type of differential staining. In this process the fixed bacterial smear is subjected to the following staining reagents in the order listed: crystal violet, iodine solution, alcohol (decolorizing agent), and safranin.

3. Which bacteria appears purple-violet colour after staining?
A. Gram-positive
B. Gram-negative
C. Both Gram-positive and Gram-negative
D. Neither Gram-positive nor Gram-negative
Answer: A
Clarification: Gram-positive bacteria retain the crystal violet and hence appear deep purple-violet colour as it has a higher content of the peptidoglycan layer. Gram-negative bacteria have lesser amount of peptidoglycan layer and on treatment with alcohol it loses the purple-violet colour, are counterstained by safranin and hence appears red.

4. Which of the following are true for Gram-negative bacteria?
A. upon alcohol treatment, the permeability of the cell wall increases
B. crystal violet-iodine (CV-I) complex is extracted
C. pore size decreases and the CV-I complex cannot be extracted
D. alcohol treatment increases the permeability of the cell wall and the CV-I complex can be extracted
Answer: D
Clarification: Experimental evidence suggests that during staining of Gram-negative bacteria the alcohol treatment extracts the lipid, which results in increased permeability of the cell wall. Thus the crystal violet-iodine (CV-I) complex can be extracted and the Gram-negative organism is decolorized. These cells subsequently take on the color of the safranin counterstain.

5. Gram-positive bacteria are usually more susceptible to?
A. streptomycin
B. tetracyclin
C. penicillin
D. ampicillin
Answer: C
Clarification: Gram-positive bacteria are usually more susceptible to penicillin and less susceptible to disintegration by mechanical treatment or exposure to some enzymes than Gram-negative bacteria. Gram-negative bacteria are more susceptible to other antibiotics like streptomycin.

6. Which of the staining technique helps in demonstrating spore structure in bacteria as well as free spores?
A. Acid-fast stain
B. Endospore stain
C. Capsule stain
D. Flagella stain
Answer: B
Clarification: There are numerous other staining techniques designed to identify some particular feature of cell structure or composition. Endospore staining demonstrates spore structure in bacteria as well as free spores.

7. In Gram-staining, iodine is used as a ______________
A. fixative
B. mordant
C. solublizer
D. stain
Answer: B
Clarification: In Gram-staining, iodine acts as a mordant i.e. it combines with the dye or stain and thereby fixes it on the material. It increases the interaction between the stain solution and the bacterial cell.

8. Which of the following is the example of Gram-negative bacteria?
A. Lactobacillus
B. Eschericia coli
C. Staphylococcus aureus
D. Bacillus subtilis
Answer: B
Clarification: Eschericia coli is an example of Gram-negative bacteria. Others are all examples of Gram-positive bacteria.

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Microbiology Multiple Choice Questions on “Energy Production by Aerobic Processes”.

1. The TCA Cycle is an _____________ pathway.
A. catabolic
B. anabolic
C. amphibolic
D. respiratory
Answer: C
Clarification: The TCA cycle is an amphibolic cycle which means that it functions not only in catabolic (breakdown) but also in anabolic (synthesis) reactions.

2. Which of the following intermediates of TCA cycle act as amino acid precursors?
A. oxaloacetic acid
B. succinic acid
C. citric acid
D. acetyl CoA
Answer: A
Clarification: Oxaloacetic acid and alpha-ketoglutaric acid are some of the intermediates of TCA cycle which act as amino acid precursors.Oxaloacetate forms aspartate which then gives us lysine and threonine.

3. Which pathway will result in the production of four carbon dioxide molecules, two ATP molecules, NADH₂ and FADH₂?
A. glycolysis
B. Krebs cycle
C. Calvin cycle
D. electron transport system
Answer: B
Clarification: Krebs Cycle is another name for TCA cycle whose overall reaction is as follows:
2Acetyl CoA+ 3H₂O + 3NAD+ + FAD+ ADP+ Pi———> 4CO₂+ 2CoA+ 2NADH₂+ 2FADH₂+ ATP.

4. The TCA cycle is regulated by which of the following enzymes?
A. citrate synthase
B. isocitrate dehydrogenase
C. malate dehydrogenase
D. succinate dehydrogenase
Answer: B
Clarification: TCA cycle is regulated by the enzyme isocitrate dehydrogenase which is sensitive to feedback inhibition by high concentration of ATP and NADH₂ and stimulation by high concentration of ADP and NAD.

5. Protein molecules can easily pass into the cell for being utilized for energy production.
A. True
B. False
Answer: B
Clarification: Protein molecules are too large to pass into the cell, bacteria secrete exoenzymes called proteases that hydrolyze exogenous proteins to peptides, which are then transported into the cell cytoplasm.

6. Which of the following pathway is common for oxidation of carbohydrates, lipids and amino acids?
A. Calvin cycle
B. Electron transport chain
C. TCA cycle
D. Pentose phosphate pathway
Answer: C
Clarification: Since acetyl-CoA is a common intermediate of carbohydrate, lipid, and amino acid metabolism so it enters the TCA cycle and hence TCA cycle is a common pathway for oxidation of carbohydrates, lipids and amino acids.

7. Phosphoenolpyruvate (PEP) is converted to oxaloacetate by the enzyme PEP deaminase.
A. True
B. False
Answer: B
Clarification: PEP is converted to oxaloacetate by the enzyme PEP carboxylase. This is a type of carbon dioxide fixing reaction.

8. The enzymes present in glyoxylate cycle are which type of enzymes?
A. reductase enzymes
B. anaplerotic enzymes
C. transferase enzymes
D. hydrolase enzymes
Answer: B
Clarification: The specific enzymes for glyoxalate cycle are isocitrate lyase and malate synthase which carry out replenishment of the pool of intermediates of the TCA cycle and hence are known as anaplerotic enzymes.

9. Which molecule will combine with the four-carbon oxaloacetate in the TCA cycle to form the six-carbon citrate?
A. lactic acid
B. NADH
C. ATP
D. acetyl-CoA
Answer: D
Clarification: The first step of the TCA cycle is the reaction between oxaloacetate and acetyl-CoA to form citrate. This acetyl-CoA comes from carbohydrate, lipid metabolism.

10. The number of ATP molecules generated in TCA cycle is _________
A. 34
B. 38
C. 24
D. 12
Answer: C
Clarification: In TCA cycle the following result is obtained:
6 NADH₂ —> 18 ATP
2 FADH₂ —> 4 ATP
2 GTP —> 2 ATP
Thus, total ATP = 24 ATP.

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Microbiology Multiple Choice Questions on “Fungi – Molds and Yeasts – Morphology”.

1. Fungi are ______________
A. prokaryotic
B. eukaryotic
C. prokaryotic and lack chlorophyll
D. eukaryotic and lack chlorophyll
Answer: D
Explanation:Fungi are eucaryotic spore-bearing protists that lack chlorophyll. They are of great practical and scientific interest to microbiologists.

2. Hyphal wall consists of microfibrils composed of ___________________
A. hemicellulose or chitin
B. cellulose
C. lipids
D. proteins
Answer:a
Clarification: The hyphal walls of fungi consist of microfibrils composed for the most part of hemicellulose or chitin; true cellulose occurs only in the walls of lower fungi.

3. Coenocytic hyphae have ________________
A. septate with uninucleate cells
B. septate with multinucleate cells
C. no septate
D. no septate with uninucleate cells
Answer: C
Clarification: Coenocytic hyphae are also known as nonseptate hyphae and hence have no sep-ta.

4. What are the dimensions of the filaments that the thallus of a fungus consists of?
A. 1 micrometre
B. 5 to 10 micrometre
C. 1 metre
D. 1 centimetre
Answer: B
Clarification: The thallus or body of a fungus consists of filaments, 5 to 10 micrometre across, which are commonly branched.

5. The yeast cell or mould filament is surrounded by a true cell wall.
A. True
B. False
Answer: A
Clarification: The yeast cell or mould filament is surrounded by a true cell wall. The exception being the slime moulds, which have a thallus consisting of a naked amoeboid mass of proto-plasm.

6. What do the term dimorphic mean?
A. Bisexual
B. Unisexual
C. Exists in two forms
D. Exists in single form
Answer: C
Clarification: Some fungi are dimorphic, that is, they exist in two forms. Some pathogenic fungi have a unicellular and yeastlike form in their host, but when growing saprophytically in soil or in laboratory medium they have a filamentous mold form.

7. Yeasts have flagella for the purpose of locomotion.
A. True
B. False
Answer: B
Clarification: Yeasts have no flagella or other organelles of locomotion.

8. The crosswalls constrict which of the following parts and then grow inwards to form septum?
A. hyphae
B. lumen
C. protoplasm
D. plasmalemma
Answer: D
Clarification: The crosswalls constrict the plasmalemma and grow inward to form generally an incomplete septum that has a central pore which allows for protoplasmic streaming.

9. Which of the following surrounds plasmalemma?
A. lumen
B. wall
C. protoplasm
D. hyphae
Answer: C
Clarification: Between the protoplasm and the wall is the plasmalemma, a double-layered mem-brane which surrounds the protoplasm.

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Microbiology Multiple Choice Questions on “Animals and Plants Viruses – Structure and Composition”.

1. Which of the following symmetry is exhibited by rod-shaped viruses?
A. icosahedral
B. helical
C. complex
D. circular
Answer: B
Clarification: The animal and plant viruses are composed of a central core of nucleic acid surrounded by a capsid, which is made up of capsomeres. They exhibit a characteristic symmetry like the rod-shaped viruses have helical symmetry.

2. The envelope surrounding the nucleocapsid of some animal viruses is made up of which of the following structures?
A. lipoproteins
B. lipopolysaccharides
C. peptidoglycan
D. chitin
Answer: A
Clarification: In some animal viruses the nucleocapsid is covered by an outer membranelike structure called the envelope, which is made up of lipoproteins and conceals the symmetry. They are sensitive to lipid solvents such as ether and chloroform.

3. Adenoviruses exhibit which of the following symmetry?
A. helical symmetry
B. circular symmetry
C. icosahedral symmetry
D. complex structure symmetry
Answer: C
Clarification: Adenoviruses which cause respiratory infections are examples of icosahedral viruses.

4. The fringes on animal viruses like influenza virus is made up of ______________
A. lipoproteins
B. glycoproteins
C. cellulose
D. polysaccharides
Answer: B
Clarification: In the influenza virus the nucleocapsid is a flexible structure packed within a fringed lipoprotein envelope. The fringes are actually spiked projections made of glycoproteins.

5. Animal and plant viruses contain both DNA and RNA in the same virion.
A. True
B. False
Answer: B
Clarification: Like bacteriophages, animal and plant viruses contain either DNA or RNA, but never both in the same virion.

6. Parvoviruses contain how many genes?
A. 100 genes
B. 500 genes
C. 40 genes
D. 3 genes
Answer: D
Clarification: If 1 kilobase is considered as the size of an average gene, small viruses like parvoviruses and picornaviruses contain perhaps 3 or 4 genes and large viruses contain several hundred.

7. In papovaviruses, DNA occurs in which of the following forms?
A. linear dsDNA
B. linear ssDNA
C. supercoiled circular dsDNA
D. supercoiled circular ssDNA
Answer: C
Clarification: In papovaviruses, DNA occurs as a supercoiled circular dsDNA. Supercoiling refers to the extra turns in the structure of dsDNA due to the action of the enzyme DNA gyrase.

8. In which of the following viruses DNA forms hairpins?
A. parvoviruses
B. herpesviruses
C. poxviruses
D. picornaviruses
Answer: A
Clarification: In ssDNA parvoviruses the terminal bases of linear DNA exist as inverted repeat sequences that form hairpins. That is, the sequence of terminal bases on each strand of such DNA maybe represented as ABCD…….D’C’B’A’, where ABCD are complementary to A’B’C’D’.

9. RNA in animal viruses exist as circular dsRNA.
A. True
B. False
Answer: B
Clarification: Some plant viruses appear to have a genome of circular dsRNA. But the RNA in animal viruses exists only as linear double-stranded or single-stranded molecules.

10. Which of the following are characteristics of the process viropexis?
A. phagocytic process
B. plant viruses penetrate host cells through ectodesmata
C. occurs by the enzyme RNA polymerase
D. phagocytic process and occurs by the enzyme lysosomal proteases
Answer: D
Clarification: Engulfment of whole virions by the cells occurs in a phagocytic process called viropexis, followed by uncoating or removal of the capsid. This takes place in the phagocytic vacuoles and is due to the action of the enzymes called lysosomal proteases.

11. Which of the following viruses carry minus-strand RNA?
A. rhabdoviruses
B. picornaviruses
C. retroviruses
D. tobacco mosaic viruses
Answer: A
Clarification: RNA viruses like rhabdoviruses, orthomyxoviruses, paramyxoviruses carry minus-strand RNA and they must first transcribe their RNA to form the plus strand that can function as mRNA. This transcription is catalyzed by a viral RNA polymerase.

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Microbiology Multiple Choice Questions on “Aquatic Microorganisms.

1. Which of the following zones have considerable rooted vegetation?
A. littoral zone
B. limnetic zone
C. profundal zone
D. benthic zone
Answer: A
Clarification: There is usually a fairly large littoral zone along the shore which has considerable rooted vegetation and includes regions where light penetrates to the bottom.

2. Which of the following layer is composed of soft mud or ooze?
A. Photic zone
B. Limnetic zone
C. Benthic zone
D. Profundal zone
Answer: C
Clarification: The benthic region is composed of soft mud or ooze at the bottom. Profundal region exists at much greater depths of the water body whereas the littoral zone is present along the shore.

3. In which of the following seasons does the nutrient concentration falls at a drastically lower level?
A. Winter
B. Spring
C. Summer
D. Autumn
Answer: C
Clarification: Occurrence of algal blooms during the spring and autumn results in lowering the nutrient concentration during summers.

4. Rapidly expanding urbanization makes it difficult to generalize upon typical microbial flora of streams.
A. True
B. False
Answer: A
Clarification: The drastic environmental changes in streams and rivers created by rapidly expanding urbanization on the one hand and changes in farming practices on the other make it impossible to generalize upon typical or characteristic microbial flora.

5. The coastal adjunct of the marine ecosystem is __________________
A. stream
B. estuary
C. river
D. lake
Answer: B
Clarification: An estuary is the coastal adjunct of the marine ecosystem. It is a semi-enclosed coastal body of water which has a free connection with the open sea.

6. The Chesapeake Bay, one of the world’s major estuarine system serves as the receiving basin for how many rivers?
A. 4
B. 6
C. 3
D. 9
Answer: D
Clarification: The Chesapeake Bay, one of the world’s major estuarine system serves as the receiving basin for nine major rivers, draining much of southern New York State, Pennsylvania, Maryland and Virginia.

7. In regions of the estuary that are nutritionally poor, it is more likely to find which of the following organisms?
A. coliforms
B. appendaged bacteria
C. viruses
D. fecal streptococci
Answer: B
Clarification: In regions of the estuary that are nutritionally poor, one is likely to find the budding and/or the appendaged bacteria, in addition to pseudomonads.

8. The characteristic color of the Red Sea is associated with heavy blooms of __________________
A. diatoms
B. cyanobacteria
C. dinoflagellates
D. chlamydomonads
Answer: B
Clarification: The characteristic color of the Red Sea is associated with heavy blooms of a cyanobacterium, Oscillatoria erythraea, which contains the pigments phycoerythrin and phycocyanin.

9. Aquatic bacteria tend to be Gram-negative.
A. True
B. False
Answer: A
Clarification: In general, aquatic bacteria tend to be Gram-negative. It is thought that the Gram-negative envelope provides a structure better suited to support life in nutritionally dilute aquatic environments than the Gram-positive cell wall.

10. Which of the following genus of bacteria is not found in fresh waters?
A. Pseudomonas
B. Flavobacterium
C. Aeromonas
D. Vibrio
Answer: D
Clarification: Species of the following genera are commonly found in freshwater: Pseudomonas,
Flavobacterium, Aeromonas and Alcaligenes. Vibrio are found in marine or estuarine waters.

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Microbiology Multiple Choice Questions on “Normal Flora and the Human Host”.

1. Who among the following was successful in raising 17 germ-free chickens for 40 days?
A. Pasteur
B. Schottelius
C. Cohendy
D. Reyniers
Answer: C
Clarification: In 1912, Cohendy at the Pasteur Institute raised 17 germ-free chickens for 40 days and concluded that vertebrate life is possible in the absence of microorganisms.

2. Within how many days after birth a stable flora develops?
A. 1 day
B. 7 days
C. 30 days
D. 7-14 days
Answer: D
Clarification: The initial flora may change considerably in composition during the first few days or weeks after birth until a stable flora becomes established and forms the normal flora.

3. Animals that are contaminated with germs are said to be gnotobiotic.
A. True
B. False
Answer: B
Clarification: Animals that are either germ-free or that live in association with one or more known organisms are said to be gnotobiotic.

4. How many day-old embryonated eggs were used by Reyniers to rear first germ-free animals?
A. 20
B. 50
C. 2
D. 7
Answer: A
Clarification: The first germ-free animals reared by Reyniers were chickens obtained by sterilizing the shells of 20-day-old embryonated eggs.

5. Which among the following was the first germ-free animal to be reared?
A. guinea pigs
B. rats
C. chickens
D. monkey
Answer: C
Clarification: The first germ-free animals reared by Reyniers were chickens obtained by sterilizing the shells of 20-day-old embryonated eggs with an effective germicide and placing them in sterile containers.

6. Which of the following vitamins are not required by normal animals?
A. Vit K
B. Vit B
C. Vit C
D. Vit A
Answer: A
Clarification: The germ-free animals require higher levels of Vitamin K, which normal animal do not require.

7. Germ-free animals require lower levels of B vitamins.
A. True
B. False
Answer: B
Clarification: Germ-free animals require higher levels of B vitamins than do normal animals, and they require vitamin K, which normal animals do not require.

8. Pseudomembranous colitis is caused by the strains of which of the following microorganism?
A. Streptococcus mutans
B. Clostridium difficile
C. Streptococcus salivarius
D. Clostridium botulinum
Answer: B
Clarification: Pseudomembranous colitis is a severe disease caused by excessive growth of toxin-producing strains of Clostridium difficile.

9. Where does the Streptococcus mutans adhere to the body site?
A. intestinal tract
B. tongue
C. teeth
D. hairs
Answer: C
Clarification: Microorganisms may often adhere specifically to one body site. Streptococcus mutans selectively binds to the smooth surface of the teeth.

10. Which of the following microorganism produces colicins in the intestine?
A. E.coli
B. B.subtilis
C. Clostridium botulinum
D. Streptococcus salivarius
Answer: A
Clarification: Many strains of E.coli in the intestines produce colicins which may help to protect the intestinal tract from closely related pathogenic bacteria.

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