MRS Mold Biology & Identification 3 — Questions and Answers
Question 1: Which mycotoxin produced by Aspergillus flavus is classified as a Group 1 human carcinogen?
- Ochratoxin A
- Aflatoxin B1 (Correct answer)
- Fumonisin B1
- Deoxynivalenol
Correct answer: Aflatoxin B1
Aflatoxin B1, produced by Aspergillus flavus and A. parasiticus, is classified by IARC as a Group 1 human carcinogen, primarily affecting the liver.
Question 2: The term 'dematiaceous' refers to molds that:
- Produce white or cream-colored colonies
- Contain melanin, appearing dark brown to black (Correct answer)
- Grow exclusively on dead organic matter
- Form large, visible fruiting bodies
Correct answer: Contain melanin, appearing dark brown to black
Dematiaceous molds contain melanin pigments in their cell walls and hyphae, giving colonies a dark brown, olive, or black appearance.
Question 3: Which of the following is NOT a common substrate for Stachybotrys chartarum growth?
- Gypsum drywall paper facing
- Ceiling tiles with cellulose content
- Concrete block walls (Correct answer)
- Water-soaked cardboard
Correct answer: Concrete block walls
Stachybotrys chartarum requires cellulose-rich materials and cannot colonize concrete, which lacks the organic substrate it needs.
Question 4: In mold taxonomy, what does 'anamorph' refer to?
- The sexual reproductive stage of a fungus
- The asexual reproductive stage of a fungus (Correct answer)
- A sterile mycelium with no reproductive structures
- A mold that cannot produce spores
Correct answer: The asexual reproductive stage of a fungus
Anamorph refers to the asexual (imperfect) stage of a fungus, while teleomorph refers to the sexual (perfect) stage.
Question 5: Which physical characteristic of mold spores most affects their ability to remain airborne for extended periods?
- Color of the spore wall
- Aerodynamic diameter and density (Correct answer)
- Chemical composition of mycotoxins
- Number of nuclei per spore
Correct answer: Aerodynamic diameter and density
Spores with small aerodynamic diameters (1–5 microns) and low density remain suspended in air longer and can penetrate deeper into the respiratory tract.
Question 6: A building inspector observes mold with a powdery, granular texture on the colony surface. This texture most likely indicates:
- Heavy production of mycelium
- Abundant surface conidia production (Correct answer)
- Presence of sexual spores only
- Thick melanin deposition
Correct answer: Abundant surface conidia production
A powdery or granular colony texture indicates abundant production of dry conidia on the colony surface, which can easily become airborne.
Question 7: Which environmental condition MOST significantly accelerates mold hyphal growth rate?
- Substrate pH of 4.5
- Temperature near the mold's optimum range (Correct answer)
- Low oxygen concentration
- High CO2 levels
Correct answer: Temperature near the mold's optimum range
Temperature near the species-specific optimum (typically 25–30°C for most building molds) most significantly accelerates hyphal extension rates.
MRS Mold Biology & Identification 3
Which mycotoxin produced by Aspergillus flavus is classified as a Group 1 human carcinogen?