Eukaryotic Microorganisms: Fungi, Algae, Protozoa, Helminths, and Arthropods

The Eukaryotes: Fungi, Algae, Protozoa, and Helminths

Defining Characteristics of Fungi

Fungi are a diverse group of eukaryotic organisms that play essential roles in ecosystems and human health.

• Cell Type: Eukaryotic, with a true nucleus and membrane-bound organelles.

• Cell Wall: Composed primarily of chitin.

• Nutrition: Heterotrophic, absorbing nutrients from organic matter.

• Growth Form: May be unicellular (yeasts) or multicellular (molds, mushrooms).

• Reproduction: Both sexual and asexual reproduction are common.

Asexual vs. Sexual Reproduction in Fungi

Fungi reproduce by both asexual and sexual means, each with distinct processes.

• Asexual Reproduction: Involves mitosis, producing genetically identical spores (e.g., conidia, sporangiospores).

• Sexual Reproduction: Involves fusion of nuclei from two mating types, followed by meiosis, producing genetically diverse spores (e.g., ascospores, basidiospores).

• Example: Rhizopus produces sporangiospores asexually and zygospores sexually.

Four Phyla of Fungi

Fungi are classified into four main phyla based on reproductive structures.

• Zygomycota: Produce zygospores; mostly molds (e.g., Rhizopus).

• Ascomycota: Produce ascospores in sac-like asci; includes yeasts and molds (e.g., Aspergillus, Saccharomyces).

• Basidiomycota: Produce basidiospores on club-shaped basidia; includes mushrooms (e.g., Agaricus).

• Deuteromycota (Imperfect Fungi): No known sexual stage; includes many pathogenic fungi.

Beneficial and Harmful Effects of Fungi

Fungi impact humans and the environment in both positive and negative ways.

• Beneficial Effects:

  • Decomposition and nutrient cycling.

  • Production of antibiotics (e.g., penicillin).

• Harmful Effects:

  • Cause diseases (mycoses) in plants and animals.

  • Food spoilage and toxin production (e.g., aflatoxins).

Lichens: Characteristics and Nutritional Needs

Lichens are symbiotic associations between a fungus and an alga or cyanobacterium.

• Structure: Consist of fungal and algal (or cyanobacterial) partners.

• Nutritional Needs: Alga provides photosynthetic products; fungus offers protection and absorbs water/minerals.

Roles of Fungus and Alga in Lichens

• Fungus: Provides structure, protection, and absorbs water/minerals.

• Alga/Cyanobacterium: Performs photosynthesis, supplying carbohydrates.

Defining Characteristics of Algae

Algae are photosynthetic eukaryotes found in aquatic environments.

• Cell Type: Eukaryotic, with chloroplasts.

• Nutrition: Photoautotrophic.

• Structure: Unicellular, colonial, or multicellular (e.g., seaweeds).

• Cell Wall: Often contains cellulose.

Outstanding Characteristics of Algal Phyla

• Chlorophyta (Green Algae): Chlorophyll a and b; mostly freshwater.

• Rhodophyta (Red Algae): Phycobilins; marine, source of agar.

• Phaeophyta (Brown Algae): Fucoxanthin pigment; marine, includes kelp.

• Bacillariophyta (Diatoms): Silica cell walls; important in aquatic food webs.

• Dinoflagellates: Two flagella; some cause red tides.

Beneficial and Harmful Effects of Algae

• Beneficial Effects:

  • Produce oxygen via photosynthesis.

  • Serve as food and industrial products (e.g., agar, carrageenan).

• Harmful Effects:

  • Some produce toxins (e.g., dinoflagellate blooms).

  • Can cause water quality issues (e.g., algal blooms).

Defining Characteristics of Protozoa

Protozoa are unicellular, eukaryotic organisms, often motile and heterotrophic.

• Cell Type: Eukaryotic, lacking cell walls.

• Nutrition: Heterotrophic, ingesting food by phagocytosis.

• Motility: Move by flagella, cilia, or pseudopodia.

• Reproduction: Mostly asexual (binary fission), some sexual.

Outstanding Characteristics of Seven Protozoan Phyla

• Sarcomastigophora: Move by flagella or pseudopodia (e.g., Amoeba).

• Ciliophora: Move by cilia (e.g., Paramecium).

• Apicomplexa: Non-motile, complex life cycles (e.g., Plasmodium).

• Microsporidia: Obligate intracellular parasites.

• Foraminifera: Have shells (tests) of calcium carbonate.

• Radiolaria: Have silica shells.

• Euglenozoa: Move by flagella; some photosynthetic (e.g., Euglena).

Intermediate Host vs. Definitive Host

Hosts are classified based on the stage of parasite development.

• Intermediate Host: Harbors the immature or asexual stage of a parasite.

• Definitive Host: Harbors the adult or sexual stage of a parasite.

• Example: Humans are the definitive host for Taenia saginata (beef tapeworm).

Cellular Slime Molds vs. Plasmodial Slime Molds

• Cellular Slime Molds: Individual cells aggregate but retain identity; form fruiting bodies.

• Plasmodial Slime Molds: Form a multinucleate, acellular mass (plasmodium); also form fruiting bodies.

Distinguishing Characteristics of Parasitic Helminths

Helminths are multicellular parasitic worms with complex life cycles.

• Body Structure: May be flat (platyhelminths) or round (nematodes).

• Reproduction: Often have elaborate reproductive systems.

• Life Cycle: Involves multiple hosts and developmental stages.

Rationale for Elaborate Life Cycle of Parasitic Worms

• Ensures survival and transmission between hosts.

• Allows adaptation to different environments and hosts.

Classes of Parasitic Platyhelminths

• Trematodes (Flukes): Leaf-shaped, complex life cycles (e.g., Schistosoma).

• Cestodes (Tapeworms): Segmented, absorb nutrients through skin (e.g., Taenia).

Parasitic Infection Host Roles

• Definitive Host: Human hosts adult tapeworms.

• Intermediate Host: Human hosts larval stages of Echinococcus.

• Both: In Taenia solium infection, humans can be both definitive and intermediate hosts.

Characteristics of Parasitic Nematodes

• Body: Cylindrical, unsegmented.

• Reproduction: Separate sexes; eggs or larvae are infective.

• Example: Ascaris lumbricoides (infective eggs), Ancylostoma (infective larvae).

Comparison of Platyhelminths and Nematodes

Feature	Platyhelminths	Nematodes
Body Shape	Flat	Round
Segmentation	May be segmented (cestodes)	Unsegmented
Digestive System	Incomplete or absent	Complete
Sexes	Often hermaphroditic	Usually separate sexes

Arthropod Vectors: Definition and Identification

Arthropods are invertebrates that may transmit pathogens as vectors.

• Vector: An arthropod that transmits pathogens between hosts.

• Examples: Mosquitoes, ticks, fleas.

Tick vs. Mosquito and Diseases Transmitted

• Tick: Arachnid; transmits Lyme disease (Borrelia burgdorferi).

• Mosquito: Insect; transmits malaria (Plasmodium).