Bacteria Morphology Questions and Answers

Answer: C

Correct answer: Mitochondria of eukaryotes

The mesosome is an infolding of the bacterial plasma membrane, and it was long regarded as the site of respiratory enzymes - hence the analogy with the mitochondrion, which does that job in eukaryotes. (Modern work suggests mesosomes are largely artefacts of chemical fixation, but the comparison is the one textbooks and examinations use.)

Answer: B

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: A

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: C

Correct answer: spinning like a propeller

The bacterial flagellum is rigid and does not beat. A rotary motor embedded in the membrane, driven by the proton-motive force, spins the helical filament like a propeller at several hundred revolutions a second. That is quite unlike the eukaryotic flagellum, which bends along its length.

Answer: B

Correct answer: flagellin

The filament and hook are built from flagellin, a globular protein that self-assembles into a hollow helical tube. Subunits travel up the hollow core and add themselves at the tip, so the flagellum grows from its far end.

Answer: B

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: Gram-negative bacteria

Fimbriae are short hair-like appendages used for attachment, and they are characteristic of gram-negative bacteria, where they are anchored in the outer membrane. They are not organs of motility - that is the flagellum - but they are important in colonisation and virulence.

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.

Answer: A

Correct answer: move

Flagella are the organelles of motility, so a bacterium without them cannot swim. It can still reproduce, grow on agar, and adhere - adhesion being the work of fimbriae. (Some non-flagellated bacteria do move by gliding or twitching, but not by swimming.)

Answer: D

Correct answer: All of these

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.