Bacteria Morphology Questions and Answers

Answer: C

The giant gut bacterium is Epulopiscium fishelsoni.

Epulopiscium lives in the intestine of the brown surgeonfish Acanthurus nigrofuscus (printed 'Acantharus') and can exceed 600 µm in length, large enough to see with the naked eye. It was first taken for a protist before being identified as a bacterium.

Vibrio fischeri is a bioluminescent symbiont of squid. Spirillum volutans is a large spiral bacterium, but only tens of micrometres long. Borrelia burgdorferi is the spirochaete that causes Lyme disease.

Answer: C

Correct answer: Mycoplasmas

Penicillin works by blocking the cross-linking of peptidoglycan, so it can only kill an organism that is building a cell wall. Mycoplasmas have no cell wall at all - only a sterol-strengthened membrane - so there is nothing for the drug to act on. Spirochaetes, cyanobacteria and bdellovibrios all have walls.

Answer: D

Correct answer: Lophotrichous

The prefixes describe the arrangement: lophotrichous is a tuft of several flagella at one pole; monotrichous a single one; amphitrichous flagella at both poles; peritrichous flagella all over the surface.

Answer: A

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.

Answer: B

Correct answer: locomote

Flagella are organs of motility: the filament is turned like a propeller by a motor in the membrane, driven by the proton-motive force. Adhesion is the work of fimbriae and pili, and reproduction has nothing to do with flagella.

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.

Answer: C

Correct answer: In the presence of a chemical compound, swimming towards or away of a bacteria

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.

Answer: B

Correct answer: O-antigen of lipopolysaccharide (LPS)

The outer face of the gram-negative outer membrane is covered with lipopolysaccharide, whose O-antigen - a long chain of repeating sugars - projects outwards. It is what the immune system recognises, and what serotypes such as E. coli O157 are named for. Braun lipoprotein anchors the outer membrane to the peptidoglycan beneath, lipoteichoic acid belongs to gram-positive walls, and the electron transport chain is in the inner membrane.

Answer: B

Correct answer: 1,4-glycosidic bond

The glycan backbone is an alternating chain of NAM and NAG joined by β-1,4-glycosidic bonds - the same linkage as in cellulose and chitin. It is precisely this bond that lysozyme hydrolyses, which is why tears and saliva can lyse many bacteria.

Answer: D

Correct answer: Corynebacterium diphtheriae

Corynebacterium diphtheriae divides by snapping fission: the cells bend sharply apart but stay joined at one end, giving the V and L shapes described as a Chinese-letter or palisade arrangement. It is a useful diagnostic clue in a stained smear.