Rose-picker's disease is caused by the yeast, Sporothrix schenkii. The yeast grows on the exteriors of rose-bush thorns. If a human gets pricked by such a thorn, the yeasts can be introduced under the skin. The yeasts then assume a hyphal morphology and grow along the interiors of lymphatic vessels until they reach a lymph node. This often results in the accumulation of pus in the lymph node, which subsequently ulcerates through the skin surface and then drains.
The answer to which of these questions would be of most assistance to one who is attempting to assign the genus Sporothrix to the correct fungal phylum?
A) Do these yeasts perform fermentation while growing on the rose-bush thorns, or do they wait until inside a human host?B) Does S. schenkii rely on animal infection to complete some part of its life cycle, or is the infection merely opportunistic?
C) Are the hyphae in lymphatic vessels septate, or are they coenocytic?
D) Is S. schenkii best described as a decomposer, parasite, pathogen, or mutualist of humans?
E) Being a yeast, does S. schenkii perform the process of budding?
Answer: B
Say S. schenkii had initially been classified as a deuteromycete. Asci were later discovered in the pus that oozed from an ulcerated lymph node, and the spores therein germinated, giving rise to S. schenkii yeasts. Which two of these are conclusions that make sense on the basis of this information?
1. S. schenkii produces asexual spores within lymph nodes.2. S. schenkii should be reclassified.
3. S. schenkii continues to have no known sexual stage.
4. The hyphae growing in lymphatic vessels probably belonged to a different fungal species.
5. S. schenkii yeasts belonging to two different mating strains were introduced by the same thorn prick.
A) 1 and 3
B) 1 and 5
C) 2 and 3
D) 2 and 5
E) 4 and 5
Answer: D
Humans have immune systems in which lymph nodes are important, because many phagocytes and lymphocytes reside there. Given that a successful infection by S. schenkii damages lymph nodes themselves, which of the following is most probable?
A) The hyphae secrete antibiotics, which increases the ability of the infected human to tolerate the fungus.B) Their conversion from yeast to hyphal morphology allows such fast growth that the body's defenses are at least temporarily overwhelmed.
C) Defensive cells of humans cannot detect foreign cells that are covered with cell walls composed of cellulose.
D) Given that most fungal pathogens attack plants, human defenses are simply not adapted to seek out and destroy fungi.
E) Given that most fungal pathogens of humans infect only the skin, human defenses are not adapted to seek out and destroy systemic fungal infections.
Answer: B
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