The NAG and NAM of the peptidoglycan layer are linked by _________
Answer: A
Correct answer: beta-(1,4) glycosidic linkage
NAG and NAM alternate along the glycan backbone, joined by β-(1,4) bonds - the linkage that gives cellulose and chitin their strength too, and the one that lysozyme cleaves. An α linkage would give a storage polymer such as starch, not a structural one.
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Which of the following are present in teichoic acids?
Answer: D
Correct answer: ribitol or glycerol residues
Teichoic acids come in two kinds, built either on ribitol phosphate or on glycerol phosphate, with the units joined by phosphodiester bonds and often carrying sugars or D-alanine. Both give the wall its negative charge.
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Chemotaxis is a phenomenon of
Answer: C
Correct answer: swimming away or towards of bacteria in presence of chemical compound
Chemotaxis is movement in response to a chemical gradient - towards an attractant such as a sugar or amino acid, and away from a repellent. The cell cannot sense a gradient across its own length, so it compares concentrations over time, lengthening its runs when conditions improve and tumbling when they worsen.
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Which of the following has Chinese letter arrangement?
Answer: D
Correct answer: Corynebacterium diphtheriae
Corynebacterium diphtheriae divides by snapping fission, so the daughter cells swing apart but stay joined at one end, producing the V and L shapes described as a Chinese-letter arrangement.
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Peptidoglycan accounts for __________ of the dry weight of cell wall in many gram positive bacteria
Answer: A
Correct answer: 50% or more
Peptidoglycan makes up half or more of the dry weight of a gram-positive wall, laid down in many layers. In gram-negative bacteria it is a single thin layer, around 10% or less, with the outer membrane accounting for much of the rest. That difference is what the Gram stain detects.
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Which of the following is not true about peptidoglycan?
Answer: D
Correct answer: None of the above
All three statements are correct: peptidoglycan is a polymer of NAG and NAM with short peptide chains; it is found in the prokaryotic cell wall; and the cross-linking makes it a single bag-shaped macromolecule (the sacculus) enclosing the whole cell. Since none of them is untrue, the answer is none of the above.
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Which of the following is surrounded by the plasmalemma?
Answer: C
Correct answer: protoplasm
The plasmalemma is the plasma membrane, and what it encloses is the protoplasm - the cytoplasm with its organelles and nuclei. Outside it lies the wall, and the lumen is the space within a hypha.
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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 are the dimensions of the filaments that the thallus of a fungus consists of?
Answer: B
Correct answer: 5 to 10 micrometre
A hypha is typically 5-10 μm across, though it may be metres long. The thallus, or mycelium, is the whole mass of such filaments - a shape that gives an enormous surface area for absorbing nutrients.
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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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