Coenocytic hyphae are ________________
Answer: C
Correct answer: no septate
Coenocytic (aseptate) hyphae have no cross-walls, so the whole filament is one long multinucleate cell with cytoplasm streaming freely along it. Septate hyphae are divided into compartments, though even their septa usually have pores that let cytoplasm and nuclei pass.
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Which of the following is analogous to mesosomes of bacteria?
Answer: A
Correct answer: Mitochondria of eukaryotes
The mesosome is an infolding of the plasma membrane, long taken to be the site of the respiratory enzymes - hence the analogy with the mitochondrion. (Electron microscopy with better fixation suggests mesosomes are largely artefacts, but the comparison is the one the syllabus expects.)
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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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When a bacterium swims towards a chemical, it is termed__________
Answer: A
Correct answer: positive chemotaxis
Movement towards an attractant is positive chemotaxis. The cell cannot measure a gradient across its own tiny length, so it compares concentrations over time: when things are improving it lengthens its runs, and when they are not it tumbles and sets off in a fresh direction.
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Teichoic acids are typically found in
Answer: A
Correct answer: cell walls of gram positive bacteria
Teichoic acids are polymers of glycerol or ribitol phosphate threaded through the peptidoglycan of gram-positive walls, some anchored to the membrane as lipoteichoic acid. They give the wall its negative charge, help bind cations, and are absent from gram-negative bacteria, which have no such layer and no outer membrane in the gram-positive sense.
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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 is true about the cell wall of gram-positive bacteria?
Answer: D
Correct answer: All of the above
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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Fungi are ______________
Answer: D
Correct answer: eukaryotic and lack chlorophyll
Fungi are eukaryotes - with a true nucleus, mitochondria and 80S ribosomes - but they have no chlorophyll, so they cannot photosynthesise and must absorb organic nutrients from their surroundings. That combination is what separates them from both plants and bacteria.
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Which of the following may be most likely to be missing from a gram-positive bacterium?
Answer: C
Correct answer: Lipopolysaccharide
LPS is a component of the outer membrane, which gram-positive bacteria do not have - so it is the one structure on the list they lack. Peptidoglycan they have in abundance, penicillin-binding proteins are the enzymes that build it, and every cell has a phospholipid membrane.
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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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