Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Chapter 11: Eukaryotic Microorganisms
Document related concepts
Transcript
Chapter 11 Outline Eukaryotic Microorganisms: The Protists, Fungi, and Helminths Introduction 11.1 Classification of Eukaryotic Organisms • The Domain Eukarya is Subdivided into Kingdoms • 16S ribosomal RNA is considered one of the most reliable methods to classify organisms • Protista • Fungi • Animalia • Plantae 11.2 The Classification and Characteristics of the Protista • The Protists Are a Perplexing Group of Microorganisms • Most are unicellular • Many are free-living, thriving in environments with water • Green algae have chloroplasts and perform photosynthesis • Some dinoflagellates cause red tides • Radiolarians have silica plates that form deposits on the ocean floor • Foraminiferans have chalky, snail-shaped skeletons • Protozoans include many motile, predatory, and parasitic protists • The Protozoa Encompass a Variety of Lifestyles • Some parabasalids live mutualistically in termite guts • Diplomonads, including Giardia intestinatlis, have bilateral symmetry • Kinetoplastids include trypanosomes, causing sleeping sickness and Leishmania • Apicomplexans include parasites such as Plasmodium and Toxoplasmosis • Amoebozoans are mostly free-living • Amoeboid motion occurs by the formation of pseudopods • Pseudopods also form food vacuoles for ingestion • Ciliates are covered with rows of hair-like cilia • The pellicle provides cell structure and stores calcium ions • Contractile vacuoles eliminate excess water • Ciliates have two types of nuclei: • macronuclei • micronuclei • Parasite Life Cycles Have Some Unique Features • The infective form of some protozoa is a trophozoite, others a cyst • The sexual cycle occurs in the definitive host • The asexual cycle occurs in the intermediate host 11.3 Characteristics and Classification of Fungi • Fungi Share a Combination of Characteristics • Fungal life cycles involve a growth phase and reproductive phase • Molds grow as long, tangled filaments of cells in visible colonies • Yeasts are unicellular fungi • • • • • • Some forms are dimorphic, growing as filamentous molds or as unicellular pathogens • Most fungi (except yeasts) exist as hyphae • A mycelium is a thick mass of hyphae • Fungal cell walls are composed of chitin • In many species, septa divide the cytoplasm into separate cells • Hyphae containing many nuclei are considered coenocytic • Fungi are heterotrophic Fungal Growth Is Influenced by Several Factors • Fungi take up nutrients through absorption • Most fungi are aerobic • Most fungi grow best at around room temperature • Many fungi thrive at slightly acidic pH (pH 5-6) • Mycorrhizae live in mutualistic symbiosis with plant roots • They help take up water and minerals • Fungal endophytes live in plant tissue, particularly leaves • Sporulation occurs in fruiting bodies • Asexual reproductive structures develop at the ends of specialized hyphae • Many asexual spores (sporangiospores) develop in sacs called sporangia Others produce unprotected spores (conidia) on conidiophores • Fragmentation of hyphae yields arthrospores • In budding, a blastospore develops from the parent cell • Fungi can also reproduce sexually • Opposite mating types come together and fuse into a heterokaryon Fungi Can Be Classified into Five Different Phyla • The Chytridiomycota (Chytrids) are related to the oldest known fungi • They are primarily aquatic • They have flagellated reproductive cells • The Glomeromycota are a group of mycorrhizae that live in over 80% of plants’ roots • Mitosporic fungi lack a sexual cycle of reproduction • Zygomycetes are terrestrial fungi that grow as mold on bread and produce • During sexual reproduction, they form a heterokaryotic diploid zygospore • Ascomycetes account for 75% of known fungi, including: • Baker’s yeast • The mold that produces penicillin • The fungus that produces aflatoxin • Candida albicans, the cause of thrush, diaper rash, and vaginitis Ascomycetes can produce: • Conidia through asexual reproduction • Ascospores through sexual reproduction Lichens are a mutualistic association between a fungus (frequently an ascomycete) and a photosynthetic organism • Basidiomycetes are club fungi, including mushrooms and puffballs • Some form mycorrhizae • • Others are plant pathogens Basidia on the gills of a mushroom cap contain sexually-produced basidiospores 11.4 The Multicellular Helminths • Flatworms (Phylum Platyhelminthes) do not have respiratory or circulatory structures or a digestive tract • Trematodes, including flukes, have complex life cycles and often two hosts • Eggs develop into larvae (miracidia) in water, which invade snails • Trematodes evade the immune system by having a surface similar to host cells • 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 • They have limited host range, but usually at least two hosts • Roundworms (Phylum Nematoda) live in every habitat on Earth • Damage to the host often occurs by large worm burdens in vessels or intestines
