ASIM'S WEBWORLD View: Main School Main AP Biology Chapter Guides RELATED LINKS Review Questions and Answers		AP BIOLOGY: Chapter Thirty-One Outline INTRODUCTION Kingdom Protista Is Artificial Grouping Most are small, single-celled organisms Many different and distinctly related groups lumped together Classification does not represent evolutionary relationships Knowledge of Protists in Greatest State of Flux Substantial research in progress May lead to additional kingdoms THE KINGDOM PROTISTA Popular Presentation of Six Kingdoms Was five until Archaebacteria split into own kingdom Protist relationships are becoming more evident fig 31.1 Protists Are Eukaryotes Important features of eukaryotes are sexuality and multicellularity Multicellularity evolved independently in several groups Protists lack specialized features of plants, animals and fungi Protists do not form embryos Do not develop complex multicellular sex organs characteristic of plants Exhibit various feeding strategies Some have chloroplasts and manufacture own food like plants Others ingest food like animals Others absorb food like fungi Historically have been included in various kingdoms Photosynthetic protists considered plants Absorbing protists included with fungi, once considered to be plants Food ingestors included with animals fig 31.2 These schemes of classification are very misleading Conventions in naming protists Botanical groups previously called divisions, now termed phyla with others Protists with chloroplasts informally called algae, studied by phycologists Heterotrophic protists informally called protozoa, studied by protozoologists Most protists are unicellular, few are multicellular Phaeophyta: brown algae, are primarily multicellular Rhodophyta: red algae, are primarily multicellular Few Chlorophyta: green algae, are multicellular fig 29.6 Multicellularity achieved independently by each group Green algae include ancestors of plants The Role of Symbiosis Two organelles of eukaryotes derived from prokaryotes Mitochondria and chloroplasts share features with bacteria Include distinctive inner membrane, different ribosomes, DNA and reproduction Mitochondria acquired once as symbionts in early history of life Arose from nonsulfur purple bacteria Lacking in amoeba-like Pelomyxa fig 31.3 Lives in muddy bottom of freshwater ponds May represent stage before symbiotic acquisition Chloroplasts exhibit three different biochemical forms Chloroplasts present in red algae Chlorophyll a, carotenoids, phycobilins Derived from cyanobacteria Chloroplasts found in brown algae, diatoms, dinoflagellates Chlorophyll a and c, carotenoids and yellow-brown pigments Derived from bacteria ancestral to Heliobacterium Chloroplasts found in green algae, plants and euglenoids Chlorophyll a and b, carotenoids Derived from bacteria ancestral to Prochloron Multiple chloroplast symbiotic events likely fig 29.4 PROTISTAN PHYLA Seven Groups Examined Here Historical, traditional artificial arrangement tbl 31.1 Photosynthesizers = Algae Heterotrophs = protozoa Absorbers = fungi-like protists Present protists here according to major shared characteristics Presence or absence of cilia or flagella Presence and kinds of pigments Type of mitosis Kinds of cristae present in mitochondria Molecular genetics of ribosomal "S" subunit Overall body form Presence and kinds of inclusions Presence of shell, test or other body armor Modes of nutrition and movement Other Classification Schemes Are Possible Molecular analysis presents clearer picture More suitable groupings will arise with further research Major characteristics of seven groups tbl 31.2 THE MOLDS Acrasiomycota: The Cellular Slime Molds fig 31.5 Once thought to be related to fungi Most closely related to amoebas Have certain characteristics that make them distinct Common in fresh water, damp soil, rotting vegetation Important group for studies on differentiation fig 31.4 Presentation of life cycle Individuals behave as individual amoebas At certain phase cells aggregate into motile slug Transforms into sorocarp, amoebas encyst as spores Some amoebas fuse sexually forming diploid macrocysts Zygotic meiosis occurs in macrocysts after a short period Other amoebas released directly to reaggregate into new slug Study chemical signals in development and differentiation in Dictyostelium Aggregation occurs when bacteria in area are eaten and starvation ensues Aggregation induced by pulses of cyclic adenosine monophosphate (cAMP) secreted by cells Spores differentiate in terminal portion of sorocarp Spores released, can release new amoeba to reinitiate cycle Myxomycota: The Plasmodial Slime Molds Consist of streaming plasmodium Lack dividing cell walls, thus multinucleate fig 31.5 Feeding phase may be yellow, orange or other color Cytoplasm exhibits conspicuous streaming Engulf and digest bacteria, yeasts, bits of organic matter Nuclei undergo mitosis in synchrony, nuclear envelop breaks down in late anaphase or telophase Lack centrioles No strong evidence indicating they are related to cellular slime molds Forms sporangium under adverse conditions fig 31.6 Spores may be diploid or haploid If diploid, meiosis occurs within 24 hours of formation Three of four nuclei disintegrate, leaving one haploid nucleus Resistant spores survive years if dry With favorable conditions release amoeboid or flagellated gametes Gametes (protoplasts) fuse to produce diploid plasmodium Oomycota Include water molds, white rusts and downy mildews Parasites or saprobes Mistakenly classified with fungi Cell walls are composed of cellulose or similar polymers Fungi cell walls composed of chitin Gametic meiosis produces a diploid phase (unlike fungi) Exhibit normal mitosis (mitosis in fungi is unusual) Possess filamentous structures called hyphae Live in freshwater or soil, many are plant or animal parasites Exhibit unique sexual reproduction Zoospores have two unequal flagella Spores produced asexually in sporangium Female gametangium called oogonium with one to eight eggs Male gametangium called antheridium with numerous male gametes Fusion produces zygote that becomes thick-walled oospore Typical water mold: Saprolegnia fig 31.7 Important plant pathogens Downy mildew of grapes Late blight of potatoes caused Irish potato famine THE SARCODINES Rhizopoda: The Amoebas Fresh and salt water specimens, abundant in soil, parasites of animals fig 31.8 Reproduction by fission, lack meiosis and sexual reproduction Lack cell walls and flagella Undergo mitosis, have typical eukaryotic spindle apparatus Related to unusual specimen of phylum Heliozoa Actinosphaerum fig 31.9 Locomotion via pseudopods fig 5.25 Cytoplasmic projections that also engulf food particles Involved with microfilaments of actin and myosin Parasitic species may form resistant cysts fig 31.24 Entamoeba histolytica : causes amoebic dysentery Cysts resist digestion by host Mitotic divisions occur in cysts, release four, eight or more amoebas Cysts dispersed in feces, transmitted via food, water, flies, direct contact Spread of disease limited by proper sanitation and hygiene A Possible Missing Link Pelomyxa palustris lacks mitochondria, does not undergo mitosis May represent early form from before symbiotic event and evolution of mitosis Nuclei divide by simple pinching apart into two nuclei Possess own special symbionts that play same role as mitochondria Assigned to own phylum, Caryoblastea Foraminifera: Forams Heterotrophic, marine organisms Variable in size Possess pore-studded shells called tests Organic matter reinforced with inorganic material Cytoplasmic extensions called podia extrude through pores fig 31.10 Podia used for swimming, gathering material for test, feeding Complex life cycles with sporic meiosis Provides extensive fossil record Used as geological markers Used as guide to oil-bearing strata Form limestone structures like White Cliffs of Dover fig 31.11 THE ALGAE Chlorophyta: The Green Algae Ancestors of all plants due to similar chloroplasts Contain chlorophylls a and b, carotinoids Similar to bacteria Prochloron and Prochlorothrix Likely candidates for symbiotic event producing Chlorophyta chloroplasts Varied group Represented by aquatic and semiterrestrial habitats Unicellular and multicellular forms Generally microscopic with few macroscopic forms like Ulva fig 29.6 Well-known genus is Chlamydomonas fig 31.12 Microscopic, unicellular and biflagellated Light sensitive eye spot orients cell for swimming Most individuals are haploid In sexual reproduction two fuse to form diploid zygote Meiosis occurs at end of resting stage, produces four haploid cells Evolutionary specialization in Chlamydomonas-like cells Nonflagellated Chlorella Reproduces only asexually Possible use as food source for humans and other animals Colonial forms leading to Volvox fig 29.6c Specialized reproductive cells give rise to new colonies Division of labor among different types of cells in colony Other growth forms Filamentous algae: Spirogyra Sheet-like algae: Ulva fig 29.6b Attaches to substrate with basal protuberances Exhibits sporic meiosis and alternation of generations fig 29.7c Haploid gametophytes resemble diploid sporophytes Complex forms: stoneworts, Chara and Nitella fig 31.13 Have whorled branches Reproductive gametangia produce gametes Rhodophyta: The Red Algae Most common warm water and coastal seaweeds Chloroplasts related to cyanobacteria Chlorophyll a and phycobilins, like cyanobacteria Cyanobacteria were likely candidates for symbiotic events Primarily multicellular fig 26.6a, 31.14 Efficiently absorb green, violet and blue lights Able to grow at greater depths than other algae Body form composed of complex, interwoven filaments Coralline algae deposit calcium carbonate in cell walls fig 31.14 Others incorporate sulfated polysaccharides like agar, carrageenan Economic importance Agar used as laboratory medium, base for cosmetics Carrageenan stabilizes paints, cosmetics and ice cream Nori cultivated for human consumption Complex life cycles involve alternation of generations, sporic meiosis Completely lack flagella and centrioles at all stages May be one of most ancient groups of eukaryotes, along with fungi Phaeophyta: The Brown Algae Mostly multicellular marine organisms Some fast growing and photosynthetically productive Conspicuous seaweeds, include kelps Possess flattened blade, stalks and anchoring base Provide food for numerous animal forms fig 31.15 Some specimens grow as large as 100 meters in length Possess chlorophyll a and c chloroplasts Chloroplasts derived from bacterium similar to Heliobacterium Exhibit alternation of generations Diploid sporophyte: large, conspicuous kelp-like form Haploid gametophyte: small, filamentous form After meiosis sporophyte produces spores, which grow into gametophyte Two different gametophytes produce male or female gametes Gametes fuse producing a zygote that becomes the sporophyte Economic importance for sodium and potassium salts, iodine and alginates THE DIATOMS Bacillariophyta: The Diatoms Photosynthetic, unicellular organisms Double shells of opaline silica resemble box with lid fig 31.16 Chloroplasts resemble that of dinoflagellates and brown algae Chlorophylls a and b, carotinoids Each group probably evolved chloroplasts independently from Heliobacterium Well-represented in living and fossil specimens Fossils produce thick sediments of diatomaceous earth Used as abrasive or paint additive Abundant in fresh and salt water habitats Grouped by radial or bilateral symmetry Shells are rigid Asexual reproduction separates shell halves Each half produces new shell within old one Organisms and shells get smaller with each consecutive division When size is too small, individual slips shell and grows to full size Individuals are diploid, meiosis occurs under starving conditions Marine diatoms produce multiple sperm, single egg Freshwater diatom gametes are ameboid and similar in appearance THE FLAGELLATES Dinoflagellata: The Dinoflagellates Unicellular, photosynthetic, mostly marine Distinctive flagella and coat, not directly related to other protists Two flagella beat in grooves cause a spinning motion Protective coat may be composed of stiff cellulose plates fig 31.17 Most have chlorophyll a and c along with carotinoids Some forms are symbionts in animals fig 40.3 Sea anemones, mollusks and corals fig 31.18a Called zooxanthellae, lack characteristic cellulose plates fig 31.18b-d Primary factor for high productivity of corals in nutrient poor water Periodic mass reproduction causes blooms and red tides Produce toxins harmful to many vertebrates Toxins accumulated by shellfish can poison humans Reproduce primary by longitudinal cell division Sexual reproduction does occur Mitosis is unique as it occurs within nucleus Chromosomes are permanently condensed Are distributed along sides of channels containing bundles of microtubules Euglenophyta: The Euglenoids Mostly fresh water organisms Group has characteristics of plants and animals Some specimens have chloroplasts and are photosynthetic Others lack chloroplasts and are heterotrophic Small size with thin flexible pellicle Reproduction via mitotic cell division Nuclear envelope remains intact through entire process No known sexual reproduction Model specimen is Euglena fig 31.15 One short, one long flagellum emerge from flask-shaped reservoir Contractile vacuoles collect excess water, pump it out reservoir Has light sensitive stigma Has numerous small chloroplasts with chlorophylls a, b and carotinoids Probable common origin of chloroplasts of euglena and green algae Two phyla otherwise unrelated Zoomastigina: The Zoomastigotes Unicellular, heterotrophic, highly variable in form fig 31.20 Possess one to thousands of flagella Free-living and parasitic forms Many reproduce only asexually, some reproduce sexually One group alternates between amoeboid and flagellated stages Many trypanosomes are human pathogens fig 31.20c;21a Cause sleeping sickness, East Coast fever, Chagas` disease Spread by various insects, such as tsetse flies fig 31.21b Attempts to produce vaccine via genetic engineering Difficult due to constant changes in glycoprotein coat Caused by gene recombination Other species inhabit guts of wood-eating insects fig 31.20b Possess enzymes capable of digesting cellulose Provide food for host Choanoflagellates are likely ancestors of all animals fig 31.20a Definite relationship to sponges Probable independent evolution into other groups Possess single flagellum, funnel-shaped contractile collar THE CILIATES Ciliophora: The Ciliates Unicellular and heterotrophic fig 31.22 Have large numbers of characteristic cilia Arranged in longitudinal rows or spirals Coordinated beating provides motility to cells Often fuse to form structures modified for feeding or locomotion Outer pellicle is tough but flexible Specialized vacuoles ingest food and regulate water fig 31.23 Food enters through gullet and passes into vacuoles Digestion occurs, wastes empty via cytoproct Two types of nuclei Micronuclei contain normal diploid chromosomes Divide by meiosis Undergo genetic recombination Macronuclei contain genes for routine cellular activities Derived from certain micronuclei after fertilization Divide by elongating and constricting Non-sexual reproduction by transverse fission fig 31.24a Sexual reproduction in Paramecium called conjugation fig 31.11b Two different mating types exchange pair of haploid micronuclei Macronucleus in each individual disintegrates Replications of micronuclei reconstitutes macronucleus THE SPOROZOANS Sporozoa: The Sporozoans Nonmotile, spore-forming animal parasites Exhibit fibrils, microtubules, vacuoles and organelles at one end Have complex life cycles with sexual and asexual phases Exhibit alternation of haploid and diploid generations Both generations also reproduce by mitosis to increase numbers Fusion of gametes produces a thick-walled cyst, the oocyst Common example Plasmodium causes malaria Sporozoite stage carried by Anopheles mosquito Injected into bloodstream, travel to liver Become merozoite and reinvade liver cells or return to bloodstream Invade red blood cells, cause them to rupture, releases toxic substances Some develop into male or female gametocytes Extracted by mosquito, become sperm or eggs Fuse forming oocysts that undergo mitosis forming sporozoites THE MOST DIVERSE KINGDOM OF EUKARYOTES Three Phyla Evolved into Three Lines of Higher Organisms Zoomastigote choanoflagellates gave rise to animals Green algae gave rise to plants Ancestry of fungi yet uncertain Other Phyla Exhibit Diverse Characteristics Mostly unicellular individuals Red and brown algae achieved multicellularity