Which group of bacteria among the following have the largest area of contact?
Answer: B
Correct answer: Trichomes
A trichome is a chain in which the cells are in broad contact along their whole adjacent walls, so the filament behaves almost as a single organism - the arrangement in many cyanobacteria. In a streptobacillus or a palisade the cells touch only at their ends or along one face.
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Which among the following are “Spirochetes”?
Answer: D
Correct answer: Treponema pallidum
Treponema pallidum, the agent of syphilis, is a spirochaete: a slender flexible helix moved by axial filaments that run inside the outer sheath rather than outside the cell. Spirillum is a rigid spiral with external flagella, which is a different group altogether.
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What is the approximate size of the bacterial cell?
Answer: D
Correct answer: 0.5 to 1.0 micrometer in diameter
A typical bacterium is about 0.5-1.0 μm across and a few micrometres long - small enough to need a light microscope at its limit, or an electron microscope for detail. The small size gives a very high surface-to-volume ratio, which is what allows such rapid exchange with the environment and such fast growth.
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When rod shaped bacteria appear in pairs, what is the arrangement called?
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.
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Surface area/volume ratio of bacteria is exceedingly low compared to the same ratio for larger organisms of similar shape.
Answer: B
Correct answer: False
The opposite is true: because surface area falls with the square of the linear dimension and volume with the cube, a very small cell has an exceedingly high surface-to-volume ratio. That is the central advantage of being small - a large membrane area serving a small cytoplasm allows rapid uptake of nutrients and rapid growth.
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A bacterium with less than a complete twist, or comma shaped, is known as
Answer: C
Correct answer: vibrioid
A vibrioid cell is a curved rod with less than one complete turn - comma-shaped, as in Vibrio cholerae. A full helix of several turns makes a spirillum if rigid, or a spirochaete if flexible.
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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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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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Salmonella typhi has which type of flagella arrangement?
Answer: B
Correct answer: Peritrichous
Salmonella, like E. coli and Proteus, is peritrichous: flagella all over the cell. When they all rotate counter-clockwise they gather into one bundle and the cell runs straight; when one reverses, the bundle breaks up and the cell tumbles into a new direction.
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The L Ring in a Gram-Negative bacterium flagella is associated with_________
Answer: B
Correct answer: Outer Membrane
The gram-negative basal body has four rings, and the letters name where each sits: L in the outer membrane (L for lipopolysaccharide), P in the peptidoglycan, and S and M at the cytoplasmic membrane. Gram-positive cells, having no outer membrane, have only the S and M rings.
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