Chapter 12 – EUKARYOTES: Protists, Fungi & Helminths 1. Protists • Algae • Protozoa 2. Fungi 3. Helminths 1. Protists A. Algae B. Protozoa A. Algae 1 Overview of the Algae Characteristics of algae: • unicellular or multicellular eukaryotes • almost all are photoautotrophs (photosynthetic) • all are essentially aquatic (live in fresh or saltwater) • all are capable of asexual reproduction • some are capable of sexual reproduction as well Algal phyla we will consider: Phaeophytes (brown algae) Diatoms Rhodophytes (red algae) Dinoflagellates Chlorophytes (green algae) Water Molds **produce an estimated 80% of O2 in the atmosphere!** Brown Algae (Phaeophyta) • macroscopic seaweeds referred to as “kelp” • largest members of the Kingdom Protista • can grow 20 cm/day • contain distinct vegetative structures • holdfast anchors kelp to surface • stemlike stipes • leaflike blades • pneumatocysts provide buoyancy Red Algae (Rhodophyta) • macroscopic seaweeds that lives in deep water where only blue light penetrates • source of “agar” (used in culture plates) • source of “carageenan” (thickening agent in foods) 2 Green Algae (Chlorophyta) • most are microscopic (uni- & multicellular), some are macroscopic • believed to have given rise to the plants Diatoms • unicellular or filamentous (form multicellular filaments) • have a unique cell wall structure composed of a carbohydrate called pectin & silica • responsible for geometric, glass-like appearance • widely distributed throughout photic zone • important part of aquatic food webs Dinoflagellates • what are commonly referred to as “plankton” • unicellular algae with 2 perpendicular flagella • some produce potent neurotoxins • source of toxic algal blooms (e.g., “red tide”) • important part of the oceanic food web 3 Water Molds (Oomycota) • have a “fungus-like” appearance but are protists • cell walls made of cellulose (not chitin) • spores have flagella (fungal cells never have flagella) • most water molds are decomposers • play an important role in recycling nutrients B. Protozoa Overview of the Protozoa Characteristics of protozoa: • all are unicellular eukaryotes lacking a cell wall • all are heterotrophs (a few can be photosynthetic) • capable of asexual reproduction (some sexual repr.) • parasitic species have complex life cycles • some form protective cysts (when times are bad) Protozoan phyla we will consider: Archaeozoa Ciliophora Microspora Euglenozoa Apicomplexa Amoebozoa 4 Archaezoa • do NOT have mitochondria • have an analogous organelle called a mitosome • most have multiple flagella • several parasitic genera can cause human disease • Trichomonas, Giardia Apicomplexa • non-motile obligate intracellular parasites • have a unique “apical complex” of fibers and vacuoles that release digestive enzymes • aid in penetration of host animal tissue • includes species of Plasmodium responsible for the disease malaria • e.g., P. vivax & P. falciparum Plasmodium vivax Life Cycle (malaria) 5 Ciliophora (“ciliates”) • all have many small projections called cilia • used for locomotion & to direct food into the • have contractile vacuole cytostome (“mouth”) to expel excess water taken in by osmosis • some have multiple nuclei (expelled by exocytosis) Sexual Reproduction in Ciliates Most ciliates are capable of sexual reproduction by a process called conjugation: • conjugating Paramecia ea produce 4 haploid micronuclei by meiosis, 3 of which disintegrate • remaining micronucleus divides by mitosis (2) • exchange of 1 micronucleus between cells • “old” & “new” micronuclei fuse, divide by mitosis, one of which replaces conjugating Paramecia original micronucleus Euglenozoa • some are photosynthetic (Euglena) • have a light-sensitive eyespot & a single flagellum • includes the hemoflagellates (Trypanosoma) • responsible for “sleeping sickness” & Chagas disease 6 Amoebozoa • aka “amoebas” • have distinct form of locomotion called “amoeboid movement” • extend cytoplasmic projections called pseudopods • also used to engulf and ingest food by phagocytosis Slime Molds • have characteristics of both amoeba & fungi but but are not true fungi • slime molds are split into 2 groups: Cellular Slime Molds • form large aggregates under unfavorable conditions • are considered part of the phylum Amoebozoa Plasmodial Slime Molds • only exist in large multinuclear aggregates • are classified in their own phylum Cellular Slime Mold Life Cycle in unfavorable conditions 7 2. Fungi Overview of the Fungi General characteristics of fungi: • all are eukaryotic absorptive heterotrophs • unicellular (yeasts) or multicellular (molds, club fungi) • capable of asexual & sexual reproduction • have cell walls that contain chitin • aerobes w/some being facultative anaerobes • vast majority are terrestrial (i.e., live on land) • all fungi develop from haploid spores (no embryos) • do NOT have flagella (spores are immotile) **study of fungi is known as mycology ** Structure of Multicellular Fungi The thallus (“body”) of a fungus consists largely of filamentous chains of cells called hyphae: • vegetative (non-reproductive) or aerial (reproductive) • some have septa (septate), some don’t (coenocytic) 8 Hyphae form a Mycelium On a rich source of nutrients, many hyphae can be produced to form a continuous mass called a mycelium. • vegetative hyphae spread across food source & “absorb” • aerial hyphae grow vertically & produce spores in a number of different ways, depending on the fungus Reproduction in Filamentous Fungi Can reproduce asexually by fragmentation: • hyphae fragments grow by mitosis Produce spores asexually or sexually: Asexual spore production • occurs at the tip of aerial hyphae • derived from single parent fungus • produced by mitosis Sexual spore production • involves a partner of opposite mating type, meiosis Asexual Spores 2 types of asexual spores: 1) those not enclosed in a sac are conidiospores (aka conidia) • produced at the end of an aerial hypha called a conidiophore 9 2) sporangiospores are produced within an enclosed sac called a sporangium • forms at the end of hypha called a sporangiophore Sexual Spores Sexual spores in fungi require 3 phases not seen in the production of asexual spores: 1) transfer of a haploid nucleus to a cell of the opposite mating type: plasmogamy 2) fusion of the haploid nuclei to form a diploid zygote nucleus: karyogamy • haploid nuclei may reproduce by mitosis before fusing • this is the ONLY occasion when fungal cells are diploid 3) meiosis to produce haploid sexual spores The 3 Fungal Phyla Zygomycota • conjugation fungi (molds) Basidiomycota • club fungi (mushrooms, smuts, rusts, puffballs) Ascomycota • sac fungi (yeasts, molds, truffles, lichens) 10 Zygomycota • molds with coenocytic hyphae (no septa) • saprophytic (feed on dead vegetation) • produce spores in sporangia Zygomycote Sexual Reproduction • plasmogamy occurs via conjugation • results in zygospore which grows a sporangium **all 3 phyla conjugate, not just “conjugating fungi”** Basidiomycota • commonly called the “club fungi” due to the presence of microscopic, club-shaped basidia: • reproductive structures that produce basidiospores • some are parasitic • many have mutualistic symbioses with various plant species 11 Basidiomycote Life Cycle • sexual reproduction via conjugation produces a basidioma: • tightly packed aerial hyphae that make up the “fruiting body” (e.g., mushroom) • basidia form on the “gills” and produce spores by meiosis Ascomycota • produce sexual ascospores in a sac-like ascus • produce asexual conidia • includes molds with septate hyphae, yeasts lichens Ascomycote Sexual Reproduction • conjugation between opposite mating types results in the formation of an ascus followed by karyogamy & meiosis (sometimes followed by mitosis) • resulting 4 or 8 ascospores released when ascus opens 12 Budding Yeasts Spherical unicellular fungi. • reproduce asexually by budding • also reproduce sexually • facultative anaerobes (used for beer, wine…) • important in biological research • studying the cell cycle • production of insulin & Saccharomyces cerevisiae other important things Fission Yeasts Oval or rod-shaped unicellular fungi. • reproduce asexually by fission • also reproduce sexually • facultative anaerobes • biological research • also very important for studying the cell cycle Schizosaccharomyces pombe Lichens Lichens are actually 2 different organisms in a mutualistic symbiosis: • cyanobacteria or green algae living among the hyphae of an ascomycote (or basidiomycote) • fungus gets free carbs! • algae or cyanobacteria protected from elements • important pioneers • can grow on inorganic surfaces, begin succession 13 Lichen Structure Fungal hyphae form the following structures: • protective cortex • inner medulla where algae grow • rhizines to attach to growth surface 3. Helminths Overview of the Helminths Helminths are parasitic worms found in 2 animal phyla, the Platyhelminthes (flatworms) and the Nematodes (roundworms). • multicellular eukaryotic heterotrophs • have complex life cycles frequently involving multiple hosts • contain distinct organ systems • some may be reduced or absent due to dependence on host (e.g., no digestive system, no locomotion) 14 Platyhelminthes (flatworms): • typically hermaphroditic (monoecious) • have a proctostome (single opening, no anus) • we will look at 2 classes: Trematodes (flukes) & Cestodes (tapeworms) Nematodes (roundworms): • typically dioecious (2 sexes) • have complete digestive system (mouth & anus) • we will look at 2 types: pinworms & hookworms Trematodes