Chapter 12: The Eukaryotes – Fungi, Algae, Protozoa, and Helminths

Chapter 12: The Eukaryotes – Fungi, Algae, Protozoa, and Helminths

Fungi

Fungi are a diverse group of eukaryotic organisms that include yeasts, molds, and mushrooms. They play essential roles in ecosystems as decomposers and have significant medical and industrial importance.

• Kingdom: Fungi

• Nutritional Type: Chemoheterotroph

• Multicellularity: All, except yeasts

• Cellular Arrangement: Unicellular, filamentous, fleshy

• Food Acquisition Method: Absorptive

• Characteristic Features: Sexual and asexual spores

• Embryo Formation: None

Mycology is the study of fungi (myco = fungus).

General Characteristics of Fungi

• Three main types: yeasts, molds, and mushrooms

• All are eukaryotic

• Most are aerobic or facultatively anaerobic; a few are anaerobic

• Of ~100,000 fungal species, only about 200 are pathogenic

• Reproduce by means of spores, usually wind-disseminated

• Both sexual (meiotic) and asexual (mitotic) spores may be produced

• Typically non-motile, except for some (e.g., Chytrids) with a motile phase

• Exhibit alternation of generations

Vegetative Structures of Molds

• Thallus: The entire vegetative body of a fungus, consisting of long filaments of cells (hyphae) joined together

• Hypha: A long filament of cells; each fragment can grow independently

• Mycelium: A mass of hyphae that branch and intertwine

Types of Hyphae

• Septate Hyphae: Contain cross-walls (septa); units are uninucleate

• Coenocytic Hyphae: Lack septa; appear continuous with many nuclei

• Vegetative Hyphae: Obtain nutrients

• Reproductive (Aerial) Hyphae: Concerned with reproduction; project above the surface and often bear reproductive spores

• Pseudohyphae: Short chains of buds unable to detach; important for tissue invasion by Candida albicans

Fungal Spores

Fungi reproduce sexually and asexually via spores that detach from the parent and germinate into new molds. Unlike bacterial spores, fungal spores are true reproductive structures and are less tolerant to dry or hot environments.

Asexual Spores

• Most common method of asexual reproduction in fungi

• Exhibit variability in color, surface, size, shape, and arrangement

• Formed by the hyphae of one organism through mitosis and cell division

• Used for clinical identification of fungi

Type	Description	Example
Conidiospore	Unicellular or multicellular spore not enclosed in a sac; produced in chains at the end of a conidiophore	Aspergillus
Arthroconidia	Type of conidia formed by fragmentation of septate hypha into single, slightly thickened cells	Coccidioides immitis
Blastoconidia	Buds coming off the parent cell; produced by some yeasts	Candida albicans
Chlamydospore	Thick-walled spores formed by rounding and enlargement within a hyphal segment	Candida albicans
Sporangiospore	Formed within a sporangium (sac) at the end of a sporangiophore	Rhizopus

Sexual Spores

Sexual reproduction involves the fusion of nuclei from two opposite mating strains and occurs in three phases:

1. Plasmogamy: Haploid nucleus of donor cell (+) penetrates cytoplasm of recipient cell (-)

2. Karyogamy: Donor and recipient nuclei fuse to form a diploid zygote nucleus

3. Meiosis: Diploid nucleus gives rise to haploid nuclei (sexual spores), some of which may be genetic recombinants

Type	Description
Zygospore	Fusion of haploid cells produces one zygospore
Ascospore	Formed in a sac (ascus)
Basidiospore	Formed externally on a pedestal (basidium)

Major Divisions of the Fungi

Division	Sexual Spore	Asexual Spore	Common Name	Type of Hyphae
Zygomycota	Zygospore	Sporangiospore	Conjugation Fungi	Coenocytic
Ascomycota	Ascospore	Conidiospore	Sac Fungi	Septate
Basidiomycota	Basidiospore	Usually None	Club Fungi	Septate
Deuteromycota (Anamorphs)	None	Conidiospores, Sporangiospore, etc.	Imperfect Fungi	Septate

Fungal Diseases (Mycoses)

• Mycosis: Fungal infection; generally chronic and difficult to treat due to similarities between animal and fungal cells

1. Systemic Mycosis: Deep within the body, usually acquired by inhalation of spores (e.g., Histoplasmosis, Coccidioidomycosis); not contagious

2. Subcutaneous Mycosis: Beneath the skin, often from saprophytic fungi in soil or vegetation (e.g., Sporotrichosis)

3. Cutaneous Mycosis (Dermatomycosis): Affect epidermis, hair, nails; secrete keratinase; transmitted by contact

4. Superficial Mycosis: Affect hair shafts and superficial epidermis

5. Opportunistic Mycosis: Normally harmless fungi become pathogenic in immunocompromised hosts (e.g., Pneumocystis in AIDS, Stachybotrys, Mucormycosis, Aspergillosis, Candidiasis)

Algae

Algae are simple, mostly aquatic, eukaryotic photoautotrophs that lack the tissues of plants. They are important primary producers in aquatic ecosystems and can sometimes cause food poisoning.

• Kingdom: Protist

• Nutritional Type: Mainly Photoautotroph

• Multicellularity: Some

• Cellular Arrangement: Unicellular, colonial, filamentous; lack tissues (roots, stems, leaves)

• Food Acquisition Method: Diffusion

• Characteristic Features: Pigments

• Embryo Formation: None

General Characteristics of Algae

• Simple eukaryotic photoautotrophs

• Oomycotes (fungal-like algae) are chemoheterotrophs

• Can be unicellular, filamentous, or have thalli

• Some cause food poisoning

• All can reproduce asexually; sexual reproduction also occurs

• Distribution depends on nutrients, light wavelengths, and attachment surfaces

Vegetative Structures in Multicellular Algae

• Thallus: The body of the alga

• Holdfast: Anchors the alga to a surface

• Stipe: Stemlike and often hollow structure

• Blade: Leaflike structure

• Pneumatocyst: Gas-filled bladder for flotation

Major Groups (Phyla) of Algae

Phylum	Common Name
Phaeophyta	Brown algae
Rhodophyta	Red algae
Chlorophyta	Green algae
Bacillariophyta	Diatoms
Dinoflagellata	Dinoflagellates

Special Notes on Algae

• Diatoms (Bacillariophyta): Unicellular or filamentous; cell wall of pectin and silica; some produce domoic acid (toxin)

• Dinoflagellates: Unicellular, planktonic; some produce neurotoxins (e.g., saxitoxin causing paralytic shellfish poisoning)

Algal Life Cycle

• Both asexual (mitosis) and sexual (meiosis, fertilization) reproduction occur

• Life cycles may include flagellated stages

Algal Habitats

• Distribution in aquatic environments depends on light penetration (wavelength), nutrient availability, and substrate for attachment

• Different groups dominate at different depths (e.g., green algae near surface, red algae at greater depths)

Additional info: Protozoa and Helminths are also covered in the full chapter but are not included in the provided slides/images. For a complete study guide, refer to the full chapter content.