Bacteria Morphology Questions and Answers

Q: Which of the following has peptidoglycan as a major constituent of cell wall?

Correct answer: Gram-positive bacteriaPeptidoglycan is the major constituent of the gram-positive wall - half or more of its dry weight, in many layers. Gram-negative bacteria have only a thin single layer, most of their wall being outer membrane, and fungal walls are made of chitin and glucans, with no peptidoglycan at all.

Q: Which type of force drives the flagellar motion?

Correct answer: Protonmotive forceThe flagellar motor is driven by the proton-motive force - protons flowing back into the cell through the Mot channels - and not by ATP. This is why a cell whose respiration is poisoned stops swimming even while it still has ATP, and it distinguishes the bacterial flagellum sharply from the ATP-driven eukaryotic one.

Q: When rod shaped bacteria appear in pairs, what is the arrangement called?

Correct answer: DiplobacilliRods that remain attached in pairs after dividing are diplobacilli; in chains, streptobacilli. The diplo- and strepto- prefixes describe the grouping and the -bacilli or -cocci ending the shape.

Q: Which one of these has a Chinese letter arrangement?

Correct answer: Corynebacterium diphtheriaeCorynebacterium diphtheriae divides by snapping fission: the cells bend sharply apart but stay joined at one end, giving the V and L shapes described as a Chinese-letter or palisade arrangement. It is a useful diagnostic clue in a stained smear.

Q: Cord factor is a ___________

Correct answer: mycolic acid derivativeCord factor is trehalose dimycolate - a sugar esterified with two mycolic acids, the long-chain fatty acids peculiar to the mycobacterial wall. It makes M. tuberculosis grow in the serpentine cords that give it its name, and it contributes to virulence by damaging mitochondria and inhibiting the migration of leucocytes.

Q: Which is most likely to be exposed on the surface of a gram-negative bacterium?

Correct answer: Pore protein (porin)Porins span the outer membrane and form water-filled channels through which small hydrophilic molecules diffuse in, so they are exposed at the surface. Lipoteichoic acid belongs to gram-positive cells; the energy-generating proteins are in the inner membrane; and the phospholipids of the outer membrane face inwards, with LPS on the outer leaflet.

Q: Which of the following bacterial genera (that produces endospore) have medical importance?

Correct answer: Both (a) and (b)The two medically important endospore-forming genera are Clostridium - tetanus, botulism, gas gangrene - and Bacillus, which includes anthrax and a food-poisoning species. The endospore matters clinically because it survives boiling, drying and disinfectants, so autoclaving is needed to destroy it.

Q: The cell walls of many gram positive bacteria can be easily destroyed by the enzyme known as

Correct answer: lysozymeLysozyme hydrolyses the β-1,4 bond between NAM and NAG in peptidoglycan. A gram-positive cell, whose wall is mostly peptidoglycan and exposed to the outside, is destroyed by it readily; a gram-negative one is protected by its outer membrane. Lysozyme is present in tears, saliva and egg white as a first line of defence.

Q: In the classification of bacteria according to shape, which among the following refer to cuboidal arrangement of bacterial cells?

Correct answer: SarcinaeSarcinae divide in three perpendicular planes and stay together, giving cubical packets of eight. Dividing in two planes gives flat tetrads, in one plane chains or pairs, and at random, clusters.

Q: The arrangement, in which flagella are distributed all round the bacterial cell, is known as

Correct answer: peritrichousPeritrichous means flagella distributed over the whole surface - the arrangement in E. coli and Salmonella. When they all turn counter-clockwise they gather into a single bundle that drives a straight run; when one reverses, the bundle flies apart and the cell tumbles.

81.

Which of the following has peptidoglycan as a major constituent of cell wall?

A.Gram-negative bacteria
B.Gram-positive bacteria
C.Fungi
D.None of these

Answer: B

Correct answer: Gram-positive bacteria

Peptidoglycan is the major constituent of the gram-positive wall - half or more of its dry weight, in many layers. Gram-negative bacteria have only a thin single layer, most of their wall being outer membrane, and fungal walls are made of chitin and glucans, with no peptidoglycan at all.

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82.

Which type of force drives the flagellar motion?

A.Protonmotive force
B.ATP driven
C.Protonmotive and ATP driven
D.No protonmotive nor ATP driven

Answer: A

Correct answer: Protonmotive force

The flagellar motor is driven by the proton-motive force - protons flowing back into the cell through the Mot channels - and not by ATP. This is why a cell whose respiration is poisoned stops swimming even while it still has ATP, and it distinguishes the bacterial flagellum sharply from the ATP-driven eukaryotic one.

Discuss in Forum

83.

When rod shaped bacteria appear in pairs, what is the arrangement called?

A.Diplobacilli
B.Streptobacilli
C.Diplococci
D.Staphylococci

Answer: A

Correct answer: Diplobacilli

Rods that remain attached in pairs after dividing are diplobacilli; in chains, streptobacilli. The diplo- and strepto- prefixes describe the grouping and the -bacilli or -cocci ending the shape.

Discuss in Forum

84.

Which one of these has a Chinese letter arrangement?

A.Clostridium tetani
B.Mycobacterium tuberculosis
C.Bacillus anthracis
D.Corynebacterium diphtheriae

Answer: D

Correct answer: Corynebacterium diphtheriae

Corynebacterium diphtheriae divides by snapping fission: the cells bend sharply apart but stay joined at one end, giving the V and L shapes described as a Chinese-letter or palisade arrangement. It is a useful diagnostic clue in a stained smear.

Discuss in Forum

85.

Cord factor is a ___________

A.protein
B.teichoic acid derivative
C.mycolic acid derivative
D.carbohydrate

Answer: C

Correct answer: mycolic acid derivative

Cord factor is trehalose dimycolate - a sugar esterified with two mycolic acids, the long-chain fatty acids peculiar to the mycobacterial wall. It makes M. tuberculosis grow in the serpentine cords that give it its name, and it contributes to virulence by damaging mitochondria and inhibiting the migration of leucocytes.

Discuss in Forum

86.

Which is most likely to be exposed on the surface of a gram-negative bacterium?

A.Pore protein (porin)
B.Protein involved in energy generation
C.Lipoteichoic acid
D.Phospholipids

Answer: A

Correct answer: Pore protein (porin)

Porins span the outer membrane and form water-filled channels through which small hydrophilic molecules diffuse in, so they are exposed at the surface. Lipoteichoic acid belongs to gram-positive cells; the energy-generating proteins are in the inner membrane; and the phospholipids of the outer membrane face inwards, with LPS on the outer leaflet.

Discuss in Forum

87.

Which of the following bacterial genera (that produces endospore) have medical importance?

A.Clostridium
B.Bacillus
C.Both (a) and (b)
D.None of these

Answer: C

Correct answer: Both (a) and (b)

The two medically important endospore-forming genera are Clostridium - tetanus, botulism, gas gangrene - and Bacillus, which includes anthrax and a food-poisoning species. The endospore matters clinically because it survives boiling, drying and disinfectants, so autoclaving is needed to destroy it.

Discuss in Forum

88.

The cell walls of many gram positive bacteria can be easily destroyed by the enzyme known as

A.lipase
B.lysozyme
C.pectinase
D.peroxidase

Answer: B

Correct answer: lysozyme

Lysozyme hydrolyses the β-1,4 bond between NAM and NAG in peptidoglycan. A gram-positive cell, whose wall is mostly peptidoglycan and exposed to the outside, is destroyed by it readily; a gram-negative one is protected by its outer membrane. Lysozyme is present in tears, saliva and egg white as a first line of defence.

Discuss in Forum

89.

In the classification of bacteria according to shape, which among the following refer to cuboidal arrangement of bacterial cells?

A.Tetrads
B.Staphylococci
C.Sarcinae
D.Streptococci

Answer: C

Correct answer: Sarcinae

Sarcinae divide in three perpendicular planes and stay together, giving cubical packets of eight. Dividing in two planes gives flat tetrads, in one plane chains or pairs, and at random, clusters.

Discuss in Forum

90.

The arrangement, in which flagella are distributed all round the bacterial cell, is known as

A.lophotrichous
B.amphitrichous
C.peritrichous
D.monotrichous

Answer: C

Correct answer: peritrichous

Peritrichous means flagella distributed over the whole surface - the arrangement in E. coli and Salmonella. When they all turn counter-clockwise they gather into a single bundle that drives a straight run; when one reverses, the bundle flies apart and the cell tumbles.

Discuss in Forum

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