Eukaryotes: Fungi, Algae, Protozoa, and Helminths

Chapter 12: Eukaryotes

Introduction

This chapter explores the diversity, structure, function, and significance of eukaryotic microorganisms, focusing on fungi, algae, protozoa, helminths, and their interactions with humans and the environment.

Fungi (Mycology)

Definition and General Functions

• Mycology is the study of fungi, a kingdom of eukaryotic organisms distinct from plants, animals, and bacteria.

• Fungi play essential roles as decomposers, recyclers of nutrients, symbionts, and pathogens.

Differences Between Bacteria and Fungi

• Fungi are eukaryotic; bacteria are prokaryotic.

• Fungi have chitin in their cell walls; bacteria have peptidoglycan.

• Fungi reproduce by spores; bacteria reproduce by binary fission.

• Fungi are generally larger and have complex cellular structures.

Yeasts and Dimorphism

• Yeasts are unicellular fungi, typically oval or spherical, reproducing by budding or fission.

• Dimorphism refers to the ability of some fungi (notably pathogenic yeasts) to exist in both yeast and mold forms, depending on environmental conditions.

Anatomy of Molds

• Hyphae: Long, branching filaments; can be vegetative (nutrient-absorbing) or aerial (spore-producing).

• Thallus: The body of a mold, composed of hyphae.

• Mycelium: A mass of hyphae forming the visible part of the fungus.

Fungal Reproduction

• Asexual spores:

  • Conidiospores: Free spores not enclosed in a sac.

  • Sporangiospores: Spores formed within a sac (sporangium).

• Sexual spores:

  • Zygospores: Formed by the fusion of two haploid cells.

Nutritional Adaptations

• Fungi can grow in environments with low moisture, low pH, and high osmotic pressure.

• They are heterotrophic, absorbing nutrients from their surroundings.

Classification: The Four Phyla of Fungi

Phylum	Key Features
Zygomycota	Coenocytic hyphae, produce zygospores
Ascomycota	Septate hyphae, produce ascospores in asci
Basidiomycota	Septate hyphae, produce basidiospores on basidia
Deuteromycota (Fungi Imperfecti)	No known sexual stage

Fungal Infections (Mycoses)

Type	Definition	Example
Systemic mycosis	Deep within the body	Histoplasmosis
Subcutaneous mycosis	Beneath the skin	Sporotrichosis
Cutaneous mycosis	Affecting hair, skin, nails	Ringworm (Dermatophytes)
Superficial mycosis	On surface of skin/hair	Piedra
Opportunistic mycosis	In immunocompromised hosts	Candidiasis

Economic Effects of Fungi

• Saccharomyces cerevisiae: Used in baking, brewing, and biotechnology.

• Taxomyces: Source of taxol, an anticancer drug.

Lichens

Definition and Morphology

• Lichen: A symbiotic association between a fungus and a photosynthetic partner (alga or cyanobacterium).

• Three main morphology groups:

  • Crustose: Crust-like, tightly attached to substrate.

  • Foliose: Leaf-like, loosely attached.

  • Fruticose: Shrub-like, branching.

Anatomy of a Lichen

• Medulla: Inner fungal layer.

• Rhizine: Root-like structures for attachment.

• Cortex: Protective outer layer.

Uses of Lichens

• Indicators of air quality, sources of dyes, and food for animals.

Algae

Major Groups and Unique Features

Group	Key Features	Example/Significance
Green algae	Chlorophyll a & b, cellulose walls	Chlamydomonas
Brown algae	Multicellular, algin in cell walls	Kelp (food, alginates)
Red algae	Phycobilins, agar production	Agar, carrageenan
Diatoms	Silica cell walls, produce domoic acid	Domoic acid toxicosis
Dinoflagellates	Plankton, some produce saxitoxins	Red tides, paralytic shellfish poisoning
Oomycota	Water molds, cellulose walls	Phytophthora infestans (potato blight)

Importance of Algae in Nature

• Primary producers in aquatic ecosystems, generate oxygen, form the base of food webs.

Protozoa

Key Terms and Life Cycle Features

• Sporozoite: Infective stage in some protozoa (e.g., malaria).

• Trophozoite: Active, feeding stage; merozoites are a stage in malaria.

• Schizogony: Asexual reproduction by multiple fission.

• Conjugation: Sexual process involving exchange of genetic material.

• Pellicle: Flexible outer covering.

• Cytosome: Cell mouth for ingesting food.

Protozoan Diseases and Organisms

Disease	Organism	Key Features
Giardiasis	Giardia lamblia	Flagellate, causes diarrhea
Trichomoniasis	Trichomonas vaginalis	Flagellate, sexually transmitted
Leishmaniasis	Leishmania spp.	Transmitted by sandflies
Chagas disease	Trypanosoma cruzi	Transmitted by reduviid bugs
African sleeping sickness	Trypanosoma brucei	Tsetse fly vector
Amebic dysentery	Entamoeba histolytica	Causes severe diarrhea
Toxoplasmosis	Toxoplasma gondii	Transmitted by cats, dangerous in pregnancy
Cryptosporidiosis	Cryptosporidium spp.	Waterborne diarrhea
Malaria	Plasmodium spp.	Complex life cycle, mosquito vector
Balantidiasis	Balantidium coli	Only ciliate human pathogen

• Definitive host: Host in which sexual reproduction occurs (e.g., mosquito for malaria).

• Intermediate host: Host in which asexual reproduction occurs (e.g., human for malaria).

Helminths

Specializations for Parasitism

• Reduced digestive, nervous, and locomotor systems; enhanced reproductive systems.

Dioecious vs. Monoecious

• Dioecious: Separate male and female individuals.

• Monoecious: Both sexes in one individual (hermaphroditic).

Trematodes (Flukes)

• Flat, leaf-shaped, with suckers for attachment.

• Examples:

  • Paragonimus: Lung fluke, causes paragonimiasis.

  • Schistosoma: Blood fluke, causes schistosomiasis.

Cestodes (Tapeworms)

• Segmented, ribbon-like body; scolex (head) with suckers/hooks; proglottids (reproductive segments).

• Humans can be definitive (adult tapeworm) or intermediate hosts (larval stage).

Nematodes (Roundworms)

• Cylindrical, unsegmented, complete digestive system.

• Examples:

  • Trichuris trichiura: Whipworm

  • Enterobius vermicularis: Pinworm

  • Dirofilaria immitis: Dog heartworm

Vectors and Vector-Borne Diseases

Definition and Classes

• Vector: An organism that transmits pathogens between hosts.

• Classes:

  • Arachnidia: Ticks, mites (e.g., Lyme disease)

  • Crustacea: Copepods (e.g., Guinea worm disease)

  • Insecta: Mosquitoes, flies, fleas (e.g., malaria, plague)

Transmission Mechanisms

• Mechanical transmission: Passive transport of pathogens (e.g., housefly feet).

• Biological transmission: Pathogen develops or multiplies within the vector (e.g., malaria in mosquitoes).

Examples of Vector-Borne Diseases

• Malaria (mosquitoes), Lyme disease (ticks), Chagas disease (reduviid bugs), African sleeping sickness (tsetse flies), plague (fleas).

Additional info: Where details were not specified, standard textbook examples and definitions were provided for completeness.