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Quizzes > Science > Biology

Test Your Mycology Skills with Our Dimorphic Fungi Quiz

Explore dimorphic fungi characteristics and yeast to mold transitions - take the quiz now!

Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art illustration of dimorphic fungi yeast and mold forms framing quiz title on teal background

Are you ready to explore the fascinating world where fungi capable of dimorphism grow either as yeast or mold? This free scored quiz will challenge what you know about dimorphic fungi characteristics and the temperature preference of dimorphic fungi, guide you through yeast to mold transition fungi processes, and reveal essential mycology dimorphic fungi facts. Perfect for students, hobbyists, and science buffs alike, you'll sharpen your understanding and test yourself with an engaging fungi quiz . For those eager to dive deeper into the shifts between single cells and filamentous forms, don't miss our yeast identification quiz . Take the quiz now and ignite your mycological passion!

Which of the following fungi is a dimorphic organism and causative agent of histoplasmosis?
Histoplasma capsulatum
Candida albicans
Aspergillus fumigatus
Cryptococcus neoformans
Histoplasma capsulatum is a thermal dimorphic fungus that grows as a mold in soil and as a yeast in host tissues, causing histoplasmosis. It is endemic in the Ohio and Mississippi River Valleys and can cause pulmonary and disseminated disease. Candida albicans can exhibit dimorphism in vitro but is primarily an opportunistic pathogen of mucosal surfaces. CDC Histoplasmosis
At what temperature do most dimorphic fungi convert to their yeast form within the human host?
25°C
30°C
37°C
42°C
Thermal dimorphism refers to the switch from a mold form at environmental temperatures (around 25°C) to a yeast (or spherule) form at body temperature (37°C) in host tissues. This transition is critical for pathogenicity. Temperatures above 40°C may impair fungal growth rather than induce the yeast phase. NCBI Textbook of Medical Mycology
Which dimorphic fungus is commonly referred to as the “Chicago disease”?
Blastomyces dermatitidis
Histoplasma capsulatum
Paracoccidioides brasiliensis
Coccidioides immitis
Blastomyces dermatitidis causes blastomycosis, historically known as “Chicago disease” due to its early description in that region. It produces broad-based budding yeast in host tissue. Histoplasma causes Darling’s disease, Paracoccidioides causes South American blastomycosis, and Coccidioides causes Valley fever. CDC Blastomycosis
In tissue specimens, Coccidioides immitis typically appears as:
Broad-based budding yeast
Spherule filled with endospores
Tuberculate macroconidia
Multiple-budding yeast (pilot’s wheel)
Coccidioides immitis forms large spherules containing numerous endospores in tissue. These spherules enlarge and release endospores upon rupture, propagating infection. Broad-based buds are characteristic of Blastomyces, tuberculate macroconidia of Histoplasma, and pilot’s wheel budding of Paracoccidioides. CDC Coccidioidomycosis
Which of the following is an endemic dimorphic fungus in Latin America, producing a multiple-budding yeast?
Paracoccidioides brasiliensis
Histoplasma capsulatum
Sporothrix schenckii
Talaromyces marneffei
Paracoccidioides brasiliensis causes paracoccidioidomycosis in South and Central America and shows a characteristic pilot’s wheel morphology with multiple narrow-based buds. Histoplasma forms small yeasts, Sporothrix forms cigar-shaped yeasts, and Talaromyces (formerly Penicillium) marneffei produces fission yeast. CDC Paracoccidioidomycosis
At 25°C in culture, Sporothrix schenckii typically grows as:
Broad-based budding yeast
Tuberculate macroconidia
Mold with conidia on hyphae
Spherule with endospores
Sporothrix schenckii exhibits a mold form at 25°C with delicate, branching hyphae bearing small conidia in rosettes. In tissue or at 37°C, it assumes a yeast form that is cigar-shaped. This dimorphic shift is important in pathogenesis. CDC Sporotrichosis
Which fungus was reclassified from Penicillium to Talaromyces and is dimorphic in Southeast Asia?
Talaromyces marneffei
Blastomyces dermatitidis
Histoplasma capsulatum
Coccidioides immitis
Talaromyces marneffei (formerly Penicillium marneffei) is a thermal dimorphic fungus endemic to Southeast Asia. It grows as a mold at 25°C producing red pigment and as a fission yeast at 37°C. This organism primarily affects immunocompromised hosts. CDC Penicilliosis
What term describes the ability of fungi to grow as mold in the environment and yeast in host tissues?
Thermotolerance
Thermal dimorphism
Polymorphism
Pleomorphism
Thermal dimorphism is the reversible switch between mold at lower temperatures and yeast (or spherule) at body temperature. This property is a key virulence factor for many systemic pathogenic fungi. Polymorphism and pleomorphism refer more generally to variable shapes. NIH Mycology Overview
The disease ‘Valley fever’ is caused by which dimorphic fungus?
Coccidioides immitis
Histoplasma capsulatum
Blastomyces dermatitidis
Paracoccidioides brasiliensis
Valley fever, or coccidioidomycosis, is caused by Coccidioides immitis (and C. posadasii) and is endemic to the southwestern United States and parts of Mexico. Infection occurs by inhalation of arthroconidia. Other dimorphic fungi cause different systemic mycoses. CDC Valley Fever
Which diagnostic test often detects Histoplasma capsulatum antigen in urine?
Latex agglutination
Galactomannan assay
Enzyme immunoassay (EIA)
Beta-D-glucan test
An enzyme immunoassay (EIA) for Histoplasma antigen in urine and serum is highly sensitive for acute and disseminated histoplasmosis. Galactomannan is used for Aspergillus, and beta-D-glucan is a broad fungal marker. Latex agglutination is less commonly used. CDC Histoplasmosis Diagnosis
Which dimorphic fungus forms broad-based budding yeast in tissue samples?
Blastomyces dermatitidis
Paracoccidioides brasiliensis
Histoplasma capsulatum
Sporothrix schenckii
Blastomyces dermatitidis produces characteristic broad-based budding yeast in tissue. Paracoccidioides has multiple narrow-based buds, Histoplasma forms small budding yeasts within macrophages, and Sporothrix has cigar-shaped yeasts. CDC Blastomycosis Diagnosis
What is the most common route of infection for systemic dimorphic fungi?
Ingestion of spores
Direct skin inoculation
Inhalation of spores or conidia
Person-to-person contact
Most systemic dimorphic fungi infect humans through inhalation of airborne spores or conidia. Once inhaled, they transform to the yeast (or spherule) form in the lungs and may disseminate. Some, like Sporothrix schenckii, can also infect via skin inoculation but this is secondary. NIH Mycology Overview
Which of the following is NOT typically a dimorphic fungal pathogen?
Aspergillus fumigatus
Histoplasma capsulatum
Blastomyces dermatitidis
Coccidioides immitis
Aspergillus fumigatus is a mold that does not convert into a yeast form at body temperature and thus is not dimorphic. Histoplasma, Blastomyces, and Coccidioides are classic thermal dimorphic fungi. CDC Aspergillosis
What is the characteristic colony morphology of Histoplasma capsulatum at 25°C?
Rosette of microconidia
Tuberculate macroconidia
Broad-based budding yeast
Spherule with endospores
At 25°C, Histoplasma capsulatum grows as a mold producing tuberculate (spiny) macroconidia. Microconidia may also be present but are not tuberculate. These features help differentiate it from other molds. NCBI Textbook of Medical Mycology
Which T-helper cell response is most important for controlling systemic dimorphic fungal infections?
Th2 response with IL-4
Th17 response with IL-17
Th1 response with IFN-?
Treg response with IL-10
A Th1 immune response characterized by interferon-gamma production is essential for activating macrophages to kill intracellular dimorphic fungi. Th2 responses are less effective and may worsen disease. Th17 and Treg have roles but are not primary for these pathogens. NCBI Th1 Immunity
Which histological stain best highlights the spherules of Coccidioides in tissue?
Periodic acid–Schiff (PAS)
India ink
Mucicarmine
Gram stain
The PAS stain colors fungal cell walls magenta and is excellent for visualizing Coccidioides spherules and endospores in tissue sections. India ink is used for Cryptococcus, mucicarmine highlights capsule, and Gram stain is less sensitive. NIH Mycology Overview
Paracoccidioides brasiliensis yeast cells often show a characteristic appearance termed:
Broad-based budding
Pilot’s wheel
Tuberculate macroconidia
Spherule formation
Paracoccidioides brasiliensis yeast cells exhibit multiple narrow-based buds radiating from a central mother cell, resembling a pilot’s wheel. This morphology aids histological diagnosis. Other forms are characteristic of different fungi. CDC Paracoccidioidomycosis
What is the first-line oral treatment for mild to moderate blastomycosis?
Fluconazole
Voriconazole
Itraconazole
Amphotericin B
Itraconazole is the recommended first-line oral therapy for mild-to-moderate blastomycosis due to its efficacy and safety profile. Amphotericin B is reserved for severe or CNS disease. Fluconazole has less activity, and voriconazole is not standard for blastomycosis. CDC Blastomycosis Treatment
Which cell wall component of dimorphic fungi most strongly stimulates macrophage activation?
Chitin
Mannoprotein
?-(1,3)-glucan
Melanin
?-(1,3)-glucan in the fungal cell wall is recognized by pattern recognition receptors on macrophages and dendritic cells, triggering a proinflammatory response. Chitin and mannoproteins are less potent, and melanin is primarily a virulence factor. NCBI ?-Glucan Immunity
In the laboratory, the conversion of a dimorphic fungus from mold to yeast form is confirmed by a:
Capsule induction test
Reversal (dimorphism) test
Agglutination assay
Antigen detection assay
A reversal test involves subculturing the organism from mold to yeast conditions and back to demonstrate true thermal dimorphism. This confirms species identification. Agglutination and antigen tests are diagnostic but do not show morphologic conversion. NIH Mycology Techniques
Histoplasma capsulatum var. duboisii, causing African histoplasmosis, is primarily found in:
North America
Western Europe
Sub-Saharan Africa
Southeast Asia
Histoplasma capsulatum var. duboisii is endemic to sub-Saharan Africa and causes African histoplasmosis with skin and bone lesions. The classic var. capsulatum is found in the Americas. It differs in clinical presentation and morphology. WHO Histoplasmosis
Which environmental form of Coccidioides immitis is primarily responsible for infecting humans?
Yeast cells
Spherules
Arthroconidia
Macroconidia
In the environment, Coccidioides immitis grows as a mold producing arthroconidia that become airborne and are inhaled. Inside the host, arthroconidia transform into spherules. Yeast cells and macroconidia are not part of its life cycle. CDC Coccidioides Biology
Which stain is most commonly used to visualize broad-based budding yeast of Blastomyces in clinical specimens?
Gram stain
Gomori methenamine silver (GMS)
India ink
Mucicarmine
GMS stain highlights fungal cell walls in black, making broad-based budding yeast of Blastomyces dermatitidis readily visible against a light background. Gram stain is less sensitive for fungi. India ink and mucicarmine are used for Cryptococcus. NCBI Mycology Stains
Sporothrix schenckii infection is most often acquired via:
Inhalation of arthroconidia
Traumatic inoculation through plant material
Person-to-person contact
Ingestion of spores
Sporotrichosis, or rose gardener’s disease, typically follows traumatic inoculation of Sporothrix schenckii from thorns or plant matter. The fungus then forms subcutaneous nodules. Inhalation and ingestion are not usual routes. CDC Sporotrichosis
Paracoccidioidomycosis is most prevalent in which population or region?
Southeast Asia
Midwestern USA
Rural South America
Sub-Saharan Africa
Paracoccidioidomycosis is endemic to rural areas of South America, especially Brazil, where the fungus lives in soil. Agricultural workers are at increased risk. It is not found in the other listed regions. WHO Paracoccidioidomycosis
Talaromyces marneffei produces what distinctive diffusible pigment at 25°C?
Green pigment
Yellow pigment
Red pigment
Blue pigment
Talaromyces marneffei produces a characteristic red diffusible pigment when grown at 25°C in culture. This feature helps distinguish it from related species. Other dimorphic fungi do not typically produce this pigment. CDC Penicilliosis
Chronic pulmonary coccidioidomycosis can radiographically resemble which other pulmonary disease?
Pneumocystis pneumonia
Pulmonary tuberculosis
Aspergilloma
Histoplasmosis
Chronic pulmonary coccidioidomycosis often leads to cavitary lesions in the lungs that mimic those seen in pulmonary tuberculosis. Both conditions can present with cough, weight loss, and night sweats. Aspergillomas can colonize these cavities but are secondary, and histoplasmosis tends to cause lymphadenopathy. CDC Clinical Coccidioidomycosis
Which biosafety level is required for culture of Coccidioides species in a reference laboratory?
BSL-1
BSL-2
BSL-3
BSL-4
Because Coccidioides arthroconidia are highly infectious by inhalation, laboratory culture requires Biosafety Level 3 conditions with respiratory protection. BSL-2 is insufficient, and BSL-4 is reserved for the most dangerous agents with no known treatment. CDC BMBL Guidelines
Histoplasma capsulatum evades the host immune response by primarily surviving within which cell type?
Neutrophils
Eosinophils
Alveolar macrophages
Dendritic cells
Histoplasma capsulatum yeasts are phagocytosed by alveolar macrophages and survive intracellularly by modulating the phagosomal environment. This intracellular niche allows dissemination and evasion of other immune defenses. Neutrophils play a role but are less central. NCBI Intracellular Histoplasma
Which transcription factor is critical for regulating the yeast-phase program in Histoplasma capsulatum?
RYP1
PacC
GAL4
SREBP
The RYP1 (Required for Yeast Phase) transcription factor governs the switch to yeast growth in Histoplasma capsulatum at 37°C. Loss of RYP1 prevents yeast-phase differentiation and attenuates virulence. PacC responds to pH, GAL4 regulates galactose metabolism, and SREBP is involved in sterol regulation. NCBI RYP1 Study
The primary adhesion and virulence factor BAD1 is associated with which dimorphic fungus?
Blastomyces dermatitidis
Coccidioides immitis
Histoplasma capsulatum
Paracoccidioides brasiliensis
BAD1 (Blastomyces adhesin-1) is a cell-surface adhesion molecule that mediates attachment to host cells and modulates immune responses in Blastomyces dermatitidis. It is essential for virulence and is not found in other dimorphic fungi. NCBI BAD1 Research
Which glycoprotein antigen (gp43) is used in serodiagnosis of which dimorphic fungal infection?
Histoplasmosis
Blastomycosis
Paracoccidioidomycosis
Coccidioidomycosis
The gp43 glycoprotein antigen is secreted by Paracoccidioides brasiliensis and is the basis for serological tests detecting antibodies in paracoccidioidomycosis. It is not used for other systemic mycoses. NCBI gp43 Study
How are endospores released in the tissue form of Coccidioides spp.?
Budding off yeasts
Rupture of spherules
Fragmentation of hyphae
Exocytosis
In host tissue, Coccidioides spherules enlarge and then rupture to release numerous endospores, each capable of forming new spherules. This mechanism propagates infection locally. It does not form yeasts or hyphal fragments in tissue. NCBI Coccidioides Biology
Which cytokine is essential for granuloma formation during dimorphic fungal infections?
IL-4
IL-10
TNF-?
IL-17
Tumor necrosis factor-alpha (TNF-?) is critical for macrophage activation and maintenance of granulomas that contain dimorphic fungi. Anti–TNF therapies can precipitate reactivation of latent infection. IL-4 and IL-10 are associated with Th2 and regulatory responses, respectively. NCBI TNF in Fungal Immunity
Which molecular technique can differentiate Histoplasma capsulatum from Blastomyces dermatitidis in a clinical sample?
Western blotting
PCR targeting ITS region
ELISA for fungal antigens
Galactomannan assay
PCR assays targeting the internal transcribed spacer (ITS) region of ribosomal DNA can specifically identify and differentiate among dimorphic fungi, including Histoplasma and Blastomyces. ELISAs and galactomannan have cross-reactivity and are less specific. NCBI PCR Mycology
Which serologic assay is most commonly used for early diagnosis of coccidioidomycosis?
Complement fixation
Latex agglutination
Indirect immunofluorescence
Western blot
Complement fixation tests detect Coccidioides-specific antibodies and are commonly used to support early diagnosis and monitor disease severity. Latex agglutination is less used, and immunofluorescence/Western blot have more specialized roles. CDC Coccidioidomycosis Diagnosis
Ambient pH influences dimorphic switching in some fungi via which transcription factor?
PacC
RYP1
HSP90
AP1
PacC is a pH-responsive transcription factor that regulates fungal gene expression and morphology in response to ambient pH. It can influence dimorphic transitions in fungi sensitive to pH changes. RYP1 controls temperature response, HSP90 is a heat shock protein, and AP1 regulates oxidative stress. NCBI PacC Function
Candida albicans switches between yeast and hyphal forms through activation of which signaling pathway?
cAMP-PKA pathway
MAPK JNK pathway
NF-?B pathway
STAT3 pathway
The cAMP-protein kinase A (PKA) signaling pathway is a primary regulator of yeast-to-hypha transition in Candida albicans, contributing to virulence. MAPK pathways also play roles but cAMP-PKA is central. NF-?B and STAT3 are host immune pathways. NCBI Candida Morphogenesis
Talaromyces marneffei infections are most commonly reported in which region?
South America
Sub-Saharan Africa
Southeast Asia
Europe
Talaromyces marneffei is endemic to Southeast Asia, including Thailand, Vietnam, and southern China. It causes penicilliosis, especially in HIV-infected individuals. It is rare outside this region. CDC Penicilliosis
What role does the YPS3 gene play in Paracoccidioides brasiliensis?
Controls ?-glucan synthesis
Mediates thermal tolerance and cell wall remodeling
Regulates iron acquisition
Codes for a secreted protease
YPS3 encodes a protein required for adaptation to host temperature and remodeling of the Paracoccidioides cell wall during the yeast phase. Mutants lacking YPS3 show attenuated virulence. It is not directly involved in ?-glucan synthesis, iron uptake, or protease secretion. NCBI YPS3 Study
Which host pattern recognition receptor specifically recognizes ?-glucan from dimorphic fungi?
TLR4
Dectin-1
NOD2
Mannose receptor
Dectin-1 is a C-type lectin receptor on macrophages and dendritic cells that specifically binds ?-(1,3)-glucan in fungal cell walls, triggering phagocytosis and cytokine production. TLR4 recognizes lipopolysaccharide, NOD2 senses muramyl dipeptide, and the mannose receptor binds mannoproteins. NCBI Dectin-1 Review
Which advanced molecular technique is most suited for profiling gene expression changes during the dimorphic transition of Histoplasma capsulatum?
Quantitative PCR
RNA sequencing (RNA-seq)
Western blot analysis
Mass spectrometry proteomics
RNA sequencing (RNA-seq) provides a comprehensive, quantitative profile of transcriptome-wide gene expression, making it ideal for studying the regulatory networks underlying the dimorphic switch in Histoplasma capsulatum. qPCR is limited to targeted genes, while proteomics and Western blot analyze proteins. NCBI RNA-seq Fungi
Which heat shock protein is essential for thermal dimorphism in Blastomyces dermatitidis?
Hsp60
Hsp70
Hsp90
Hsp100
Hsp90 is a molecular chaperone critical for stabilizing proteins during heat stress and is essential for the mold-to-yeast transition in Blastomyces dermatitidis. Inhibition of Hsp90 impairs the dimorphic switch and attenuates virulence. Other heat shock proteins have roles in stress response but Hsp90 is key for thermal sensing. NCBI Hsp90 Fungal Dimorphism
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Study Outcomes

  1. Understand Dimorphic Fungi Growth -

    Explain how fungi capable of dimorphism grow either as yeast or mold and the environmental triggers that drive their morphological shifts.

  2. Identify Temperature Preferences -

    Describe the temperature preference of dimorphic fungi and how thermal conditions determine whether they exist in yeast or mold form.

  3. Analyze Infection Modes -

    Differentiate between inhalation, cutaneous, and systemic modes of infection employed by pathogenic dimorphic fungi.

  4. Recognize Unique Yeast Forms -

    Recall specific yeast-to-mold transition fungi and their specialized yeast forms during human infection.

  5. Apply Mycology Dimorphic Fungi Facts -

    Use key mycology dimorphic fungi facts to tackle quiz questions and reinforce your understanding of fungal pathogenesis.

  6. Evaluate Quiz Performance -

    Assess your mastery of dimorphic fungi characteristics by interpreting your quiz score and identifying areas for further study.

Cheat Sheet

  1. Thermal Dimorphism and Temperature Preference -

    Fungi capable of dimorphism grow either as yeasts at 37°C in host tissues and as molds at 25°C in the environment, often remembered with the phrase "Yeast in heat, mold in cold." This thermal dimorphism is regulated by temperature-sensitive gene expression (e.g., DRK1 in Blastomyces) and is central to pathogenicity (CDC, ASM).

  2. Key Dimorphic Pathogens and Mnemonic -

    A useful mnemonic "High Blast Cocci Party Sporadically" helps recall the main dimorphic fungi: Histoplasma capsulatum, Blastomyces dermatitidis, Coccidioides spp., Paracoccidioides brasiliensis, and Sporothrix schenckii. Recognizing these fungi capable of dimorphism grow either as environmental molds producing infectious spores or as yeasts/spherules in tissue is essential for diagnosis (University research).

  3. Infection Route and Morphological Shift -

    Dimorphic fungi typically infect via inhalation of mold-form conidia, which then convert to yeast in the lungs to evade immunity; for example, Histoplasma capsulatum conidia inhaled into alveoli transform into budding yeasts. Understanding this yeast to mold transition fungi undergo in hosts explains why respiratory exposure often leads to systemic disease (WHO, medical journals).

  4. Diagnostic Culture and Microscopy -

    When culturing dimorphic fungi, lab technicians grow samples at 25°C to observe mold structures and at 37°C to confirm yeast-phase morphology, a process called the "conversion test." Microscopic features like Blastomyces' broad-based buds and Coccidioides' spherules help distinguish species and inform appropriate treatment (ASM Manual, CDC guidelines).

  5. Clinical Implications and Virulence Factors -

    Thermal dimorphism influences virulence, as the yeast phase expresses surface proteins (e.g., BAD1 in Blastomyces) that facilitate immune evasion. Studying these dimorphic fungi characteristics guides antifungal therapy development and highlights the importance of temperature preference in pathogenesis (peer-reviewed research).

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