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 Roles

• Mycology is the study of fungi, including their genetic and biochemical properties, taxonomy, and use to humans.

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

Comparison: Fungi vs. Bacteria

• Cell Type: Fungi are eukaryotic; bacteria are prokaryotic.

• Cell Wall: Fungi have chitin; bacteria have peptidoglycan.

• Reproduction: Fungi reproduce sexually and asexually; bacteria reproduce asexually (binary fission).

• Nutrition: Fungi are heterotrophic; bacteria can be autotrophic or heterotrophic.

Yeasts

• Yeasts are unicellular fungi, typically oval or spherical.

• They reproduce by budding or fission.

• Some yeasts exhibit dimorphism, existing as yeast at 37°C and as mold at 25°C.

Mold Anatomy

• Hyphae: Long, branching filaments. Two types:

  • Vegetative hyphae: Obtain nutrients.

  • Aerial hyphae: Involved in reproduction.

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

• Mycelium: A mass of hyphae visible to the naked eye.

Fungal Reproduction

• Asexual spores:

  • Conidiospores: Not enclosed in a sac.

  • Sporangiospores: Enclosed in a sac (sporangium).

• Sexual spores:

  • Zygospores: Formed by fusion of two similar cells.

Nutritional Adaptations

• Fungi can grow in acidic, low-moisture, and high-osmotic-pressure environments.

• They are capable of metabolizing complex carbohydrates.

Fungal Phyla

Phylum	Key Features
Zygomycota	Coenocytic hyphae, zygospores
Ascomycota	Septate hyphae, ascospores in sacs
Basidiomycota	Basidiospores on basidia
Deuteromycota	Imperfect fungi, no known sexual stage

Fungal Infections (Mycoses)

Type	Description	Example
Systemic	Deep within body, affect multiple organs	Histoplasmosis
Subcutaneous	Beneath the skin	Sporotrichosis
Cutaneous	Affect hair, skin, nails	Ringworm (Tinea)
Superficial	On hair shafts, surface skin	Piedra
Opportunistic	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: Symbiotic association between a fungus and a photosynthetic partner (alga or cyanobacterium).

• Morphology groups:

  • Crustose: Flat, crust-like

  • Foliose: Leaf-like

  • Fruticose: Shrub-like

Anatomy of a Lichen

• Medulla: Inner fungal layer

• Rhizine: Root-like structure for attachment

• Cortex: Protective outer layer

Uses of Lichens

• Indicators of air quality

• Sources of dyes, antibiotics, and food

Algae

Phyla and Features

Phylum	Key Features	Example/Significance
Green algae	Chlorophyll a & b, cellulose walls	Ancestor of land plants
Brown algae	Multicellular, algin in cell walls	Kelp, used as thickener
Red algae	Phycobiliproteins, agar in cell walls	Agar production
Diatoms	Silica cell walls	Domoic acid toxicosis
Dinoflagellates	Plankton, cellulose plates	Saxitoxins, red tides
Oomycota	Water molds, cellulose walls	Phytophthora infestans (potato blight)

Importance of Algae

• Primary producers in aquatic ecosystems

• Generate oxygen via photosynthesis

• Form the base of many food webs

Protozoa

Key Terms and Life Cycle Stages

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

• Trophozoite: Active, feeding stage

• Merozoite: Stage in malaria, produced by schizogony

• Schizogony: Asexual reproduction by multiple fission

• Conjugation: Sexual process involving exchange of genetic material

• Pellicle: Flexible outer covering

• Cytosome: Cell mouth for ingestion

Protozoan Diseases

Disease	Organism	Key Features
Giardiasis	Giardia lamblia	Intestinal infection, cysts in water
Trichomoniasis	Trichomonas vaginalis	Sexually transmitted, no cyst stage
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	Bloody diarrhea, cysts in water
Toxoplasmosis	Toxoplasma gondii	Transmitted by cats, dangerous in pregnancy
Cryptosporidiosis	Cryptosporidium spp.	Waterborne, resistant to chlorine
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

Adaptations for Parasitism

• Specialized attachment organs (suckers, hooks)

• Reduced digestive and nervous systems

• Complex reproductive systems

Reproductive Terms

• Dioecious: Separate male and female individuals

• Monoecious: Both sexes in one individual (hermaphroditic)

Trematodes (Flukes)

• Flat, leaf-shaped bodies

• Oral and ventral suckers

• Examples:

  • Paragonimus: Lung fluke

  • Schistosoma: Blood fluke, causes schistosomiasis

Cestodes (Tapeworms)

• Segmented, ribbon-like bodies

• Scolex: Head with suckers/hooks

• Proglottids: Reproductive segments

• Humans can be definitive (harbor adult) or intermediate (harbor larval) hosts

Nematodes (Roundworms)

• Cylindrical, unsegmented bodies

• Separate sexes (mostly dioecious)

• 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 of vectors:

  • Arachnida: Ticks, mites

  • Crustacea: Crabs, copepods

  • Insecta: Mosquitoes, flies, fleas, lice

Transmission Types

• 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 (mosquito)

• Lyme disease (tick)

• Chagas disease (reduviid bug)

• Leishmaniasis (sandfly)

• Plague (flea)