Bacteria Questions and Answers

Q: Volutin granules are demonstrated by

Correct answer: Loeffler’s techniqueVolutin (metachromatic) granules are polyphosphate stores, and they stain a different colour from the rest of the cell with methylene blue - the metachromasia that gives them their name. Loeffler’s alkaline methylene blue is the classic method, and Neisser’s stain is used for the same purpose in Corynebacterium diphtheriae.

Q: The organ of locomotion of bacteria is

Correct answer: flagellaFlagella are the organelles of motility: a rotary motor in the membrane, driven by the proton-motive force, spins the helical filament like a propeller. Fimbriae are for attachment, and capsules and slime layers for protection.

Q: Which of this bacteria is resistant to penicillin as it lacks a cell wall?

Correct answer: MycoplasmasPenicillin blocks the cross-linking of peptidoglycan, so it can only act on a cell that is building a wall. Mycoplasmas have none - only a sterol-strengthened membrane - so the drug has nothing to attack. Spirochaetes, cyanobacteria and bdellovibrios all have walls.

Q: Gram’s staining consist of

Correct answer: 4 stagesThe Gram stain has four steps: the primary stain (crystal violet), the mordant (iodine), decolourisation with alcohol or acetone, and the counterstain (safranin). The third is the critical one - too long, and even gram-positive cells lose the dye.

Q: A gram-positive bacterium retains the crystal violet stain because

Correct answer: bacteria have thick peptidoglycan layerRetention is a matter of wall thickness. The many layers of peptidoglycan in a gram-positive wall dehydrate and shrink when alcohol is applied, trapping the crystal violet-iodine complex inside. The teichoic acids and the absence of a periplasm are genuine features of such cells, but they are not what holds the dye.

Q: Which of the following is true about the structure of the gram-negative cell wall

Correct answer: include outer membraneThe defining feature of the gram-negative wall is the outer membrane, whose outer leaflet is lipopolysaccharide. The other two statements are false: its peptidoglycan layer is thin, and it does have a periplasmic space - the compartment between the two membranes.

31.

Volutin granules are demonstrated by

A.Ozeshki’s staining
B.Burri’s technique
C.Loeffler’s technique
D.Morozov’s staining

Answer: C

Correct answer: Loeffler’s technique

Volutin (metachromatic) granules are polyphosphate stores, and they stain a different colour from the rest of the cell with methylene blue - the metachromasia that gives them their name. Loeffler’s alkaline methylene blue is the classic method, and Neisser’s stain is used for the same purpose in Corynebacterium diphtheriae.

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32.

The organ of locomotion of bacteria is

A.capsule
B.flagella
C.slime
D.fimbriae

Answer: B

Correct answer: flagella

Flagella are the organelles of motility: a rotary motor in the membrane, driven by the proton-motive force, spins the helical filament like a propeller. Fimbriae are for attachment, and capsules and slime layers for protection.

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33.

Which of this bacteria is resistant to penicillin as it lacks a cell wall?

A.Spirochetes
B.Cyanobacteria
C.Mycoplasmas
D.Bdellovibrios

Answer: C

Correct answer: Mycoplasmas

Penicillin blocks the cross-linking of peptidoglycan, so it can only act on a cell that is building a wall. Mycoplasmas have none - only a sterol-strengthened membrane - so the drug has nothing to attack. Spirochaetes, cyanobacteria and bdellovibrios all have walls.

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34.

Hemolytic serum for complement fixation reaction is obtained in the following manner

A.rabbits are immunized by suspension of sheep erythrocytes
B.sheep are immunized by suspension of rabbits erythrocytes
C.guinea pig are immunized by suspension of sheep erythrocytes
D.rabbits are immunized by suspension of guinea pig erythrocytes

Answer: A

Correct answer: rabbits are immunized by suspension of sheep erythrocytes

Haemolytic serum is anti-sheep-red-cell antibody, and it is raised by injecting rabbits with sheep erythrocytes. The rabbit serum is then heated to destroy its own complement, so that the only complement in the final test is the one being measured.

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35.

Gram’s staining consist of

A.2 stages
B.4 stages
C.3 stages
D.5 stages

Answer: B

Correct answer: 4 stages

The Gram stain has four steps: the primary stain (crystal violet), the mordant (iodine), decolourisation with alcohol or acetone, and the counterstain (safranin). The third is the critical one - too long, and even gram-positive cells lose the dye.

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36.

A gram-positive bacterium retains the crystal violet stain because

A.cell wall include significant amount of teichoic and lipoteichoic acids
B.bacteria have thick peptidoglycan layer
C.periplasmic space is absent
D.all of the above

Answer: D

Correct answer: bacteria have thick peptidoglycan layer

Retention is a matter of wall thickness. The many layers of peptidoglycan in a gram-positive wall dehydrate and shrink when alcohol is applied, trapping the crystal violet-iodine complex inside. The teichoic acids and the absence of a periplasm are genuine features of such cells, but they are not what holds the dye.

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37.

A gene is a

A.segment of DNA carrying codons specifying for a particular polypeptide
B.triple nucleotide group, coding one specific amino acid
C.triple nucleotide group, not coding one specific amino acid
D.segment of RNA

Answer: A

Correct answer: segment of DNA carrying codons specifying for a particular polypeptide

A gene is a stretch of DNA whose sequence of codons specifies one polypeptide (or one functional RNA). A single triplet is a codon, not a gene, and it specifies one amino acid.

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38.

Pandemic disease is

A.constantly present in particular area
B.spreads rapidly, involving many persons in an area at the same time
C.spreads through many areas of the world involving many persons within a short period
D.spreads slowly, involving several persons in an area at the same time

Answer: C

Correct answer: spreads through many areas of the world involving many persons within a short period

A pandemic is an epidemic that has crossed countries or continents, affecting very large numbers in a short time - influenza in 1918 and COVID-19 are the standard examples. The difference from an epidemic is one of geographical extent, not of severity.

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39.

Which of the following is true about the structure of the gram-negative cell wall

A.thick peptidoglycan layer
B.periplasmic space is absent
C.include outer membrane
D.All of the above

Answer: C

Correct answer: include outer membrane

The defining feature of the gram-negative wall is the outer membrane, whose outer leaflet is lipopolysaccharide. The other two statements are false: its peptidoglycan layer is thin, and it does have a periplasmic space - the compartment between the two membranes.

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40.

During stationary phase

A.Microorganisms increase in size of cell and metabolic rate
B.The cells start dividing and their number increase by geometric progression
C.Rate of multiplication and death becomes almost equal
D.Population of the cells decreases

Answer: C

Correct answer: Rate of multiplication and death becomes almost equal

In the stationary phase nutrients are running short and toxic products accumulating, so the rate of division falls until it exactly balances the rate of death. The viable count therefore stays level, though the cells within it are constantly being replaced. Spores and secondary metabolites are typically produced here.

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