The cocci which form bunches in an irregular pattern are
Answer: A
Correct answer: Staphylococci
Staphylococci divide in several planes at random and stay together, so they form irregular grape-like clusters - which is what the name means. Division in one plane gives pairs or chains, and in two perpendicular planes tetrads.
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Which of the following is true about cell wall of gram-positive bacteria?
Answer: D
Correct answer: All of these
All three are true of the gram-positive wall: it is built of many layers of peptidoglycan, making it much thicker than the gram-negative one, and it contains teichoic acids threaded through it. Those layers are what trap the crystal violet-iodine complex during Gram staining.
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The cocci which mostly occur in single or pairs are
Answer: B
Correct answer: Diplococci
Diplococci divide in one plane and stay attached in pairs - Neisseria and Streptococcus pneumoniae are the familiar examples. Streptococci form chains, tetracocci groups of four, and staphylococci irregular clusters; the pattern follows from the planes of division and whether the cells separate.
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Yeasts have flagella for the purpose of locomotion
Answer: B
Correct answer: False
Yeasts have no flagella and are non-motile. They spread passively, carried by air, water or insects. (A few motile spores occur among the lower fungi, but not in yeasts.)
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Gram-negative bacteria are more resistant to antibiotics due to the presence of
Answer: B
Correct answer: Outer lipopolysaccharide layer
The outer membrane, with its lipopolysaccharide leaflet, is an extra permeability barrier that many drugs simply cannot cross - hydrophobic ones are blocked by the LPS, and large hydrophilic ones are too big for the porins. That is why gram-negative bacteria are intrinsically resistant to a whole range of antibiotics that kill gram-positive ones.
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Microcapsules are composed of
Answer: D
Correct answer: all of these
A capsule or microcapsule may be built of polysaccharide, of polypeptide (as in Bacillus anthracis), or of glycoprotein and lipid material. Whatever its composition, it resists phagocytosis and helps the cell adhere - which is why capsulated strains are so often the virulent ones.
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Flagella move the cell by
Answer: C
Correct answer: spinning like a propeller
The bacterial flagellum is rigid and does not beat. A rotary motor embedded in the membrane, driven by the proton-motive force, spins the helical filament like a propeller at several hundred revolutions a second. That is quite unlike the eukaryotic flagellum, which bends along its length.
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The next to last step in peptidoglycan biosynthesis is
Answer: C
Correct answer: linking the sugar of the disaccharide-peptide unit to the growing peptidoglycan chain
The order of the last steps is: the subunit is carried across the membrane on bactoprenol, added to the growing glycan chain by transglycosylation, and only then cross-linked to a neighbouring strand by transpeptidation. So the next-to-last step is the attachment of the sugar, and cross-linking - the step penicillin blocks - is the last.
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In which of the following, lipo-polysaccharide is a major constituent of outer membrane of the cell wall?
Answer: B
Correct answer: Gram-negative bacteria
Lipopolysaccharide makes up the outer leaflet of the gram-negative outer membrane. Its lipid A portion is the endotoxin responsible for fever and shock in gram-negative sepsis, and its O-antigen the basis of serotyping. Gram-positive walls have no outer membrane, and fungi have no LPS at all.
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Which among the following acts as a transport protein for protons in flagellar motion?
Answer: D
Correct answer: Mot protein
The Mot proteins form the stator, a ring of channels around the motor through which protons flow back into the cell. The energy of that flow is what turns the rotor - the flagellum is driven by the proton-motive force, not by ATP. The Fli proteins are the switch that reverses the direction of rotation.
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