Chapter 12: Eukaryotes – Fungi, Protists, Helminths, and Arthropods

Fungi

General Characteristics

Fungi are a diverse group of eukaryotic organisms that play essential roles in ecosystems as decomposers, pathogens, and symbionts.

• Mycology: The study of fungi.

• Nutrition: Fungi are chemoheterotrophs, meaning they obtain nutrients by absorbing organic matter from their environment.

• Growth Conditions: Fungi thrive in acidic environments (pH ~5), high sugar/salt concentrations, and low moisture.

• Structure: The main body of multicellular fungi is called a mycelium, composed of threadlike filaments called hyphae.

Reproduction

• Vegetative Division: Fungi can reproduce asexually by budding (uneven division) or fission (equal division).

• Spores: Fungi produce spores for reproduction, which can be asexual (conidiospores, sporangiospores) or sexual (zygospores, ascospores, basidiospores).

Types of Fungal Spores

• Asexual Spores: Conidiospores, sporangiospores

• Sexual Spores: Zygospores, ascospores, basidiospores

Fungal Diseases (Mycoses)

• Types: Systemic, subcutaneous, cutaneous, superficial, and opportunistic mycoses.

• Example: Claviceps purpurea produces ergot toxin, which can cause hallucinations and convulsions.

Protists

General Characteristics

Protists are a diverse group of eukaryotic microorganisms that can be unicellular, multicellular, or colonial. They may be autotrophic or heterotrophic.

• Main Types: Algae, slime molds, protozoa

Protozoa

Structure and Movement

• Locomotion: Protozoa move using pseudopods, flagella, cilia, or by gliding (spore-forming types).

• Trophozoite: The active, feeding, growing stage of a protozoan.

• Cyst: A dormant stage allowing survival in harsh conditions.

Reproduction

• Asexual: Fission, budding, schizogony (multiple fission)

• Sexual: Conjugation

Protozoan Diseases

• Giardia lamblia: Causes giardiasis

• Plasmodium vivax: Causes malaria

• Toxoplasma gondii: Causes toxoplasmosis

• Entamoeba histolytica: Causes dysentery

Helminths

General Characteristics

Helminths are multicellular eukaryotic animals, many of which are parasitic.

• Major Phyla: Platyhelminthes (flatworms) and Nematoda (roundworms)

Types of Helminths

• Trematodes (Flukes): Flat, leaf-shaped

• Cestodes (Tapeworms): Flat, segmented; have a scolex (head) and proglottids (segments)

• Nematodes (Roundworms): Cylindrical, unsegmented

Examples

• Flukes: Schistosoma (blood fluke)

• Tapeworms: Taenia solium (pork tapeworm)

• Roundworms: Ascaris lumbricoides, Enterobius vermicularis (pinworm), Necator americanus (hookworm)

Arthropods as Vectors

General Characteristics

Arthropods are animals with segmented bodies, exoskeletons, and jointed legs. Some act as vectors, transmitting pathogens to humans and animals.

Types of Transmission

• Mechanical Transmission: Passive transport of pathogens (e.g., on feet or body parts)

• Biological Transmission: Pathogen multiplies within the vector before transmission

Examples of Arthropod Vectors and Diseases

Vector	Disease
Mosquito (Anopheles)	Malaria
Tick (Ixodes)	Lyme disease
Flea (Xenopsylla)	Plague

Additional info: This review sheet covers key eukaryotic microorganisms and their roles in human disease, as well as the vectors that transmit them. For more detail, refer to textbook chapters on eukaryotic pathogens and vector biology.