Chapter 11 Outline
Eukaryotic Microorganisms: The Protists, Fungi, and Helminths
Introduction
11.1 Classification of Eukaryotic Organisms
• The Domain Eukarya is Subdivided into Kingdoms
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16S ribosomal RNA is considered one of the most reliable methods to classify organisms
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Protista
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Fungi
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Animalia
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Plantae
11.2 The Classification and Characteristics of the Protista
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The Protists Are a Perplexing Group of Microorganisms
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Most are unicellular
• Many are free-living, thriving in environments with water
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Green algae have chloroplasts and perform photosynthesis
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Some dinoflagellates cause red tides
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Radiolarians have silica plates that form deposits on the ocean floor
• Foraminiferans have chalky, snail-shaped skeletons
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Protozoans include many motile, predatory, and parasitic protists
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The Protozoa Encompass a Variety of Lifestyles
• Some parabasalids live mutualistically in termite guts
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Diplomonads, including Giardia intestinatlis , have bilateral symmetry
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Kinetoplastids include trypanosomes, causing sleeping sickness and
Leishmania
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Apicomplexans include parasites such as Plasmodium and Toxoplasmosis
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Amoebozoans are mostly free-living
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Amoeboid motion occurs by the formation of pseudopods
• Pseudopods also form food vacuoles for ingestion
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Ciliates are covered with rows of hair-like cilia
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The pellicle provides cell structure and stores calcium ions
• Contractile vacuoles eliminate excess water
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Ciliates have two types of nuclei:
• macronuclei
• micronuclei
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Parasite Life Cycles Have Some Unique Features
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The infective form of some protozoa is a trophozoite, others a cyst
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The sexual cycle occurs in the definitive host
• The asexual cycle occurs in the intermediate host
11.3 Characteristics and Classification of Fungi
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Fungi Share a Combination of Characteristics
• Fungal life cycles involve a growth phase and reproductive phase
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Molds grow as long, tangled filaments of cells in visible colonies
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Yeasts are unicellular fungi

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Some forms are dimorphic, growing as filamentous molds or as unicellular pathogens
• Most fungi (except yeasts) exist as hyphae
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A mycelium is a thick mass of hyphae
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Fungal cell walls are composed of chitin
• In many species, septa divide the cytoplasm into separate cells
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Hyphae containing many nuclei are considered coenocytic
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Fungi are heterotrophic
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Fungal Growth Is Influenced by Several Factors
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Fungi take up nutrients through absorption
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Most fungi are aerobic
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Most fungi grow best at around room temperature
• Many fungi thrive at slightly acidic pH (pH 5-6)
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Mycorrhizae live in mutualistic symbiosis with plant roots
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They help take up water and minerals
• Fungal endophytes live in plant tissue, particularly leaves
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Sporulation occurs in fruiting bodies
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Asexual reproductive structures develop at the ends of specialized hyphae
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Many asexual spores (sporangiospores) develop in sacs called sporangia
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Others produce unprotected spores (conidia) on conidiophores
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Fragmentation of hyphae yields arthrospores
• In budding, a blastospore develops from the parent cell
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Fungi can also reproduce sexually
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Opposite mating types come together and fuse into a heterokaryon
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Fungi Can Be Classified into Five Different Phyla
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The Chytridiomycota (Chytrids) are related to the oldest known fungi
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They are primarily aquatic
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They have flagellated reproductive cells
• The Glomeromycota are a group of mycorrhizae that live in over 80% of plants’ roots
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Mitosporic fungi lack a sexual cycle of reproduction
• Zygomycetes are terrestrial fungi that grow as mold on bread and produce
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During sexual reproduction, they form a heterokaryotic diploid zygospore
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Ascomycetes account for 75% of known fungi, including:
• Baker’s yeast
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The mold that produces penicillin
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The fungus that produces aflatoxin
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Candida albicans , the cause of thrush, diaper rash, and vaginitis
• Ascomycetes can produce:
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Conidia through asexual reproduction
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Ascospores through sexual reproduction
• Lichens are a mutualistic association between a fungus (frequently an ascomycete) and a photosynthetic organism
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Basidiomycetes are club fungi, including mushrooms and puffballs
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Some form mycorrhizae

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Others are plant pathogens
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Basidia on the gills of a mushroom cap contain sexually-produced basidiospores
11.4 The Multicellular Helminths
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Flatworms (Phylum Platyhelminthes) do not have respiratory or circulatory structures or a digestive tract
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Trematodes, including flukes, have complex life cycles and often two hosts
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Eggs develop into larvae (miracidia) in water, which invade snails
• Trematodes evade the immune system by having a surface similar to host cells
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Cestodes, including tapeworms, have a head region called a scolex
• Fertilized eggs are produced in proglottids distant from the scolex, which break off and spread eggs
• Tapeworms generally live in a host’s intestine, absorbing nutrients
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They have limited host range, but usually at least two hosts
• Roundworms (Phylum Nematoda) live in every habitat on Earth
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Damage to the host often occurs by large worm burdens in vessels or intestines