Food Microbiology Questions and Answers

Answer: C

The match is P-3, Q-4, R-2, S-1.

• The cytoplasmic membrane is a phospholipid bilayer with embedded proteins.
• The flagellum is the organ of motility, rotated by a motor in the cell envelope.
• The bacterial cell wall is made of peptidoglycan (murein), thick in Gram-positive and thin in Gram-negative bacteria.
• Ribosomes (70S in bacteria) carry out protein synthesis.

The other options swap these, for example giving the flagellum peptidoglycan or the cell wall motility, which are wrong.

Answer: C

Aflatoxins are produced by Aspergillus flavus.

Aflatoxins B1, B2, G1 and G2 are toxic, carcinogenic secondary metabolites of A. flavus and A. parasiticus, which grow on groundnuts, maize, cottonseed and tree nuts stored warm and damp. Aflatoxin B1 is among the most potent natural liver carcinogens known.

Aspergillus niger is the industrial mould used for citric acid production and is not an aflatoxin producer. Fusarium verticillioides produces fumonisins, and Rhizopus oligosporus is the mould used to ferment tempeh.

Answer: C

The genus without a cell wall is Mycoplasma.

Mycoplasmas have no peptidoglycan cell wall at all. Their cell membrane contains sterols, which give it some strength, and they are among the smallest free-living organisms. With no wall, they are naturally resistant to penicillin and other antibiotics that act on cell-wall synthesis, and they have no fixed shape.

Lactobacillus and Staphylococcus are Gram-positive bacteria with thick peptidoglycan walls, and Escherichia is Gram-negative, with a thin peptidoglycan layer and an outer membrane; all three have cell walls.

Answer: C

The correct matching is P-2; Q-3; R-1; S-4.

• E. coli is a Gram-negative rod that does not form spores (2).
• Bacillus subtilis is a Gram-positive rod that forms endospores (3).
• Staphylococcus aureus is a Gram-positive coccus (round) that does not form spores (1).
• Listeria monocytogenes is a Gram-positive rod that does not form spores (4).

Option D swaps Bacillus and Listeria, the two Gram-positive rods, which differ only in spore formation. Options A and B mismatch E. coli or S. aureus.