The structure responsible for motility of bacteria is
Answer: B
Correct answer: flagella
Flagella drive swimming: a rotary motor in the membrane spins the helical filament like a propeller. Pili and fimbriae are for attachment and for conjugation, capsules for protection, and sheaths are structural.
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Teichoic acid present in Gram-positive bacteria can bind to which ion?
Answer: C
Correct answer: Mg ions
Teichoic acids are polymers of glycerol or ribitol phosphate, so the wall carries a strong negative charge. That charge binds divalent cations, magnesium in particular, holding a reserve of them at the cell surface where the membrane enzymes need them.
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Which of the following is exposed on the outer surface of a gram-negative bacterium?
Answer: A
Correct answer: O-antigen of lipopolysaccharide (LPS)
The outer leaflet of the gram-negative outer membrane is lipopolysaccharide, and its O-antigen - a chain of repeating sugar units - projects into the medium. It is the most exposed structure on the cell and the basis of serological typing. Braun lipoprotein anchors the membrane inwards to the peptidoglycan, and lipoteichoic acid belongs to gram-positive cells.
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Bacteria having a cluster of flagella at both poles are known as
Answer: C
Correct answer: Amphitrichous
Amphitrichous means flagella at both poles - a single one at each, or a tuft at each. Lophotrichous is a tuft at one pole only, monotrichous a single flagellum at one pole, and peritrichous flagella all over the surface.
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Which of the following are functions of stalk?
Answer: C
Correct answer: attachment of the cells to surfaces
A stalk or prostheca is an extension of the cell wall and membrane. It anchors the cell to a surface - often with a holdfast at its tip, as in Caulobacter - and by extending the cell it also increases the surface available for absorbing nutrients from dilute water.
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In which of the following is the peptidoglycan layer present in large quantity?
Answer: A
Correct answer: Gram-positive bacteria
Gram-positive walls are mostly peptidoglycan - many layers, half or more of the wall’s dry weight. Gram-negative walls have a single thin layer under an outer membrane. Fungal and algal walls contain none: they are built of chitin, glucans or cellulose.
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The cell wall of
Answer: A
Correct answer: gram-positive bacteria are thicker than gram-negative bacteria
The gram-positive wall is a thick multilayered sheet of peptidoglycan, some 20-80 nm; the gram-negative wall has only a thin layer of 2-7 nm, covered by an outer membrane. The thick layer retains the crystal violet-iodine complex when the cell is decolourised with alcohol, which is what makes the Gram stain work.
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Gram positive cells have a
Answer: B
Correct answer: multiple layer of peptidoglycan that helps to retain the crystal violet stain
The Gram stain works on wall thickness. The many layers of peptidoglycan in a gram-positive wall trap the crystal violet-iodine complex when alcohol is applied; the thin layer of a gram-negative cell does not, and its outer membrane is dissolved by the alcohol, so the cell decolourises and takes up the counterstain.
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The cell walls of Gram positive bacteria contain two modified sugars, N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). They are covalently linked by
Answer: D
Correct answer: β- 1,4-glycosidic bond
NAG and NAM alternate along the glycan backbone, joined by β-1,4-glycosidic bonds - the same linkage as in cellulose and chitin, and the one lysozyme hydrolyses. An α linkage, as in starch, would give a quite different, non-structural polymer.
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Swimming of a bacterium towards a chemical is termed
Answer: A
Correct answer: positive chemotaxis
Movement towards a chemical is positive chemotaxis; movement away from a repellent is negative chemotaxis. Phototaxis is a response to light and magnetotaxis to a magnetic field.
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