Bacteria Morphology Questions and Answers

Answer: B

The correct match is (P)-(ii), (Q)-(i), (R)-(iii), (S)-(iv).

• Flagella drive motility, which lets bacteria move toward attractants and away from repellents in chemotaxis (ii).
• The peptidoglycan cell wall resists the internal osmotic pressure and prevents cell lysis (i).
• Metachromatic (volutin) granules are stores of polyphosphate, the phosphate reserve used for ATP synthesis, which the paper calls storage for ATP (iii).
• Magnetosomes are chains of magnetite crystals that orient the cell along the Earth's magnetic field (iv).

Option A gives the cell wall a storage role, option C swaps the granules and magnetosomes, and option D gives flagella the job of preventing lysis.

Answer: D

The correct statement is that flagella originate from the basal body.

A bacterial flagellum has three parts: the basal body, a set of rings anchored in the cell envelope that acts as the rotary motor; the hook; and the long helical filament made of flagellin. The filament grows out from the basal body through the hook.

Flagella are long, typically 5 to 20 μm, far more than 0.5 to 2 μm. Each filament is a single helical structure, not a set of adjacent fibrils. Conjugation is mediated by sex pili, not flagella, which serve for motility.

Answer: A

Both [a] and [r] are true and [r] is the correct reason for [a].

Endospores survive boiling and other heat treatments that kill the vegetative cells of the same species, which is why sterilisation needs autoclaving at 121 °C.

The heat resistance comes largely from the spore core's very low water content. Calcium dipicolinate and small acid-soluble spore proteins accumulate in the core, the cortex helps keep it dehydrated, and the protoplast shrinks to a minimum volume in a gel-like state; the SASPs also bind and protect the DNA. The reason therefore explains the assertion.

Answer: C

Axial filaments are found in Treponema pallidum.

Spirochaetes such as Treponema, Borrelia and Leptospira move by axial filaments, also called endoflagella: flagella that lie in the periplasmic space, wound around the cell under the outer sheath. Their rotation makes the cell corkscrew through viscous media.

Mycobacterium tuberculosis and Pasteurella multocida are non-motile, and Shigella dysenteriae is a non-motile enteric rod; none has axial filaments.

Answer: A

The correct match is P - i; Q - ii; R - iii; S - iv.

• The cell wall, built of peptidoglycan, resists the internal turgor pressure and protects the cell from osmotic lysis.
• Fimbriae are short, numerous hair-like adhesins used for attachment to surfaces and host cells.
• Flagella are rotating filaments that provide motility.
• Pili, in particular the sex (F) pilus, bring cells together for the transfer of genetic material by conjugation.

The second option gives fimbriae motility, which they do not provide. The third and fourth swap the roles of flagella and pili or give the cell wall attachment, contradicting these standard functions.

Answer: A

Protoplasts can be generated from Streptococcus pneumoniae.

A protoplast is a cell whose wall has been removed completely, leaving only the plasma membrane. In Gram-positive bacteria the wall is a thick peptidoglycan layer with no outer membrane, so lysozyme (or growth with penicillin in an osmotically protected medium) strips it away entirely. S. pneumoniae is Gram-positive.

Brucella abortus, Pasteurella multocida and Shigella flexneri are Gram-negative. Removing their thin peptidoglycan leaves the outer membrane in place, so the product is a spheroplast, not a true protoplast.

Answer: C

The correct statement is: their growth is not inhibited by penicillin.

Mycoplasmas have no cell wall. Penicillin acts by blocking the cross-linking of peptidoglycan in the cell wall, so it has no target in a mycoplasma.

The lack of a wall also explains why the other statements are wrong. Without a rigid wall, mycoplasma cells are pleomorphic, of no definite shape, and they are sensitive to lysis by osmotic shock, being protected only by a sterol-containing membrane. They are not harmless either: Mycoplasma pneumoniae causes atypical pneumonia in humans and M. genitalium causes urethritis.

Answer: C

The characteristic absent in Archaea is peptidoglycan.

Peptidoglycan (murein), built from N-acetylglucosamine and N-acetylmuramic acid, is found only in the cell walls of Bacteria. Its absence is one of the features that separates the Archaea from them, and is why archaea are insensitive to penicillin and lysozyme.

The other three do occur in Archaea. Some methanogens have pseudomurein, a look-alike polymer that uses N-acetyltalosaminuronic acid and β-1,3 links. A paracrystalline S-layer of protein or glycoprotein is the most common archaeal cell wall. Archaea typically have a single circular chromosome, like bacteria.

Answer: A

Correct answer: monotrichous

Monotrichous is a single flagellum at one pole - the arrangement in Vibrio cholerae and Pseudomonas. Lophotrichous is a tuft at one pole and amphitrichous flagella at both.

Answer: B

Correct answer: port of entry of genetic material during mating

The F (sex) pilus is made by a donor cell carrying the F plasmid. It attaches to a recipient and draws the two cells together, and DNA then passes from donor to recipient - the process of conjugation. Ordinary fimbriae, by contrast, are for attachment to surfaces.