Biology 200 - Chapter 18: Kingdom Protista Comprehensive Study Guide

Evolutionary Background and Transitions to Land

  • Timeline of Early Life Environments:

    • For the majority of biological history, specifically until less than 11 billion years ago, organisms were entirely confined to the oceans.
    • Protection Provided by Oceans:
      • Prevention of desiccation (drying out).
      • Shielding from harmful ultraviolet radiation.
      • Buffer against large fluctuations in temperature.
      • Facilitation of nutrient intake: Organisms could absorb nutrients directly from the surrounding water medium.

  • The Transition to Terrestrial Life:

    • Life began the transition to land approximately 400400 million years ago.
    • Ancestry: Green algae are the evolutionary group that initiated the transition, eventually giving rise to green plants.
    • Coleochaete: Identified as a probable indirect ancestor of land plants due to shared biological features.
    • Shared Features with Land Plants:
      1. The presence of cells that resemble parenchyma.
      2. The development of a cell plate and phragmoplast during the process of mitosis.
      3. The production of a protective covering for the zygote.
      4. The synthesis of a lignin-like compound.

  • Microscopic Study Note:

    • According to Kingsley Stern, slides for these organisms are often viewed at 400×500400 \times 500 magnification.

Principal Characteristics of Kingdom Protista

  • Domain Eukarya:

    • All members of Kingdom Protista are eukaryotic. This domain also encompasses Kingdoms Plantae, Fungi, and Animalia.

  • Complexity:

    • Members range from simple unicellular organisms to complex multicellular organisms.

  • Nutritional Diversity: Protists utilize varied methods to obtain energy:

    • Photosynthesis.
    • Ingestion of food particles.
    • Absorption of nutrients.

  • Reproduction and Life Cycles:

    • Individual life cycles vary significantly across different phyla.
    • Reproductive Methods: Generally involves cell division (asexual) and various sexual processes.

General Overview of Algae

  • Common Ecological Examples: Algae are frequently observed as seaweed, pond scums, films on the glass of fish tanks, and colored patches in swimming pools.

  • Classification Criteria: Algae are categorized into several phyla based on three primary factors:

    1. The form and structure of their reproductive cells.
    2. The specific combinations of photosynthetic pigments they possess.
    3. The types of food reserves they store.

Phylum Chlorophyta — The Green Algae

  • Morphological Diversity:

    • Forms include unicellular organisms, filamentous structures, and platelike colonies.
    • Complex forms include netlike tubes, hollow spheres, and structures resembling lettuce leaves (e.g., Ulva).

  • Habitat and Environment:

    • Freshwater: The greatest variety exists in freshwater lakes, ponds, and streams.
    • Terrestrial and Other: Found on tree bark, animal fur, snowbanks, and rocks.
    • Symbiosis: Found in lichen partnerships and inside animals like flatworms or sponges.

  • Cellular and Storage Profile:

    • Pigments: Contain chlorophylls aa and bb.
    • Food Storage: Store carbohydrates as starch.
    • Structure: Most species have a single nucleus per cell and reproduce both sexually and asexually.

  • Representative Genus: Chlamydomonas:

    • Habitat: Common in freshwater pools.
    • Structure: Unicellular with a pair of whip-like flagella at one end for motility. Contains two or more vacuoles at the flagella base for water regulation and waste removal.
    • Chloroplast: Single, cup-shaped, containing one or two pyrenoids (proteinaceous structures for starch synthesis).
    • Red Eyespot: Located near the flagella base; sensitive to light, allowing the organism to swim toward a light source.
    • Asexual Reproduction: The nucleus undergoes mitosis, and contents divide into two daughter cells within the cellulose wall. These develop flagella and swim away as haploid cells.
    • Sexual Reproduction: Cells congregate; two cells fuse to form a zygote, which develops into a thick-walled zygospore. After dormancy, the zygospore undergoes meiosis to produce 44 haploid zoospores.

  • Representative Genus: Ulothrix:

    • Structure: A filamentous alga featuring a specialized holdfast cell at one end for substrate attachment.
    • Chloroplast: Wide, curved, and somewhat flattened, containing one to several pyrenoids.
    • Asexual Reproduction: Cell contents condense and divide via mitosis into zoospores that escape through a parent cell pore.
    • Sexual Reproduction: Cell contents condense and divide into gametes that escape to fuse with others.

  • Representative Genus: Spirogyra (Watersilk):

    • Structure: Filaments of cylindrical cells; frequently float in masses on quiet freshwater surfaces.
    • Chloroplasts: Ribbon-shaped and spirally wrapped around the central vacuole, with pyrenoids at regular intervals.
    • Reproduction: Asexual reproduction occurs exclusively via filament fragmentation. Sexual reproduction occurs via conjugation, where papillae fuse to form conjugation tubes. Protoplasts move through these tubes to fuse and form a thick-walled zygote, which later undergoes meiosis.

  • Representative Genus: Oedogonium:

    • Structure: An epiphytic (growing on other plants) filamentous green alga with a holdfast.
    • Chloroplast: Large and netlike with pyrenoids at intersections.
    • Asexual Reproduction: Occurs via fragmentation or the production of single zoospores at filament tips, which have a fringe of approximately 120120 flagella.
    • Sexual Reproduction (Oogamy): Defined by one small motile gamete (sperm) and one larger stationary gamete (egg).
      • Antheridium: Boxlike cell producing two motile sperm.
      • Oogonium: Swollen cell containing a single egg.
    • Outcome: The resulting zygote forms thick walls and produces 44 zoospores via meiosis to grow into new haploid filaments.

Other Notable Green Algae

  • Chlorella: Tiny, spherical unicellular organisms that reproduce only asexually via mitosis. Significant in research and potential food production.
  • Desmids: Mostly free-floating unicellular organisms (e.g., Closterium) that reproduce by conjugation.
  • Hydrodictyon (Water Nets): Tubular colonies forming hexagonal or polygonal meshes; reproduction is both asexual and isogamous (flagellated gametes of similar size).
  • Acetabularia (Mermaid’s Wineglass): A single huge mushroom-shaped cell used to study the nucleus's role in determining cell form. Reproduction is isogamous.
  • Volvox: A colonial alga forming a hollow ball held together by gelatinous material; daughter colonies develop inside the parent colony.
  • Ulva (Sea Lettuce): A multicellular seaweed characterized by flattened blades and a basal holdfast. It exhibits isomorphism, where haploid and diploid blades are indistinguishable in appearance.
  • Cladophora: A branched filamentous alga found in both fresh and marine water; notable for having multinucleate cells.

Phylum Chromophyta — Yellow-Green, Golden-Brown, and Brown Algae

  • Yellow-Green Algae (Xanthophyceae):

    • Motility: Motile cells have two flagella oriented in opposite directions.
    • Genus Vaucheria: Oogamous, coenocytic (multinucleate) filamentous alga. It lacks fucoxanthin (except in this genus) and reproduces asexually via aplanospores.

  • Golden-Brown Algae (Chrysophyceae):

    • Habitat: Mostly freshwater plankton.
    • Pigmentation: Yellow-brown carotenoids.
    • Motility: Two flagella of unequal length at right angles; the shorter one features a photoreceptor.

  • Diatoms (Bacillariophyceae):

    • Structure: Unicellular organisms resembling ornate glass boxes with lids.
    • Cell Walls: Composed of 95%95\% silica.
    • Pigments and Food: Contain chlorophylls aa, c1c_1, and c2c_2, plus fucoxanthin. They store energy as oils, fats, or laminarin.
    • Motility: Freshwater diatoms use a raphe (lengthwise groove) for jerky movement across surfaces.
    • Reproduction: Asexual division results in half the offspring getting smaller until sexual reproduction (forming auxospores) restores original size.

  • Brown Algae (Phaeophyceae):

    • Structure: Large complex bodies (thallus) consisting of a holdfast, stipe, and blades. None are unicellular.
    • Features: Often have gas-filled air bladders (e.g., Giant Kelp).
    • Pigments: Chlorophylls aa and cc, and fucoxanthin.
    • Cell Walls: Contain algin.
    • Genus Sargassum: Floating seaweed reproducing asexually via fragmentation.
    • Genus Fucus (Rockweed): Receptacles at branch tips contain conceptacles. The oogonium produces 88 eggs, and the antheridium produces 6464 sperm.

Phylum Rhodophyta — The Red Algae

  • Habitat: Typically found in warmer and deeper marine waters.
  • Morphology: Mostly filamentous; can appear as flattened blades.
  • Pigmentation: Colors are derived from phycobilins (similar to cyanobacteria). They contain chlorophyll and sometimes chlorophyll dd.
  • Storage: Food is stored as floridean starch.
  • Economic Value: Primary source of agar.
  • Polysiphonia Life Cycle: Extremely complex with three thallus types:
    1. Male Gametophyte: Spermatogonia produce nonmotile spermatium.
    2. Female Gametophyte: Features carpogonia.
    3. Tetrasporophyte: Produces tetraspores that germinate into new gametophytes.

Phylum Euglenophyta — The Euglenoids

  • Cellular Structure: Lack a cell wall; possess a pellicle (plasma membrane with underlying spiral strips).
  • Organelles:
    • Flagellum that pulls the cell.
    • Gullet for food ingestion.
    • 45%45\% of species have disc-shaped chloroplasts.
    • Red eyespot for light detection.
  • Storage and Repro: Stores food as Paramylon; reproduces asexually via cell division.

Phylum Dinophyta — The Dinoflagellates

  • Ecological Impact: Known for "red tides" (rapid multiplication); some produce neurotoxins that accumulate in shellfish.
  • Structure: Cellulose armor plates inside the membrane; two flagella in intersecting grooves (one serves as a rudder).
  • Cellular Features:
    • Pigments: Xanthophylls, chlorophylls aa and cc.
    • 1/31/3 of species are nonphotosynthetic.
    • Chromosomes remain condensed and visible throughout the cell life cycle.
    • Food storage: Starch.

Specialized Algal Phyla

  • Phylum Cryptophyta (Cryptomonads): Possess two flagella and internal plates. Notable for having a nucleomorph (vestigial symbiont nucleus) and a gullet with ejectosomes.
  • Phylum Prymnesiophyta (Haptophytes): Marine plankton with two smooth flagella and a third flagellum called a haptonema for food capture; often scale-covered.
  • Phylum Charophyta (Stoneworts): Inhabit shallow freshwater and precipitate calcium salts. Feature a main axis with whorled branches and multicellular antheridia (oogamous).

Human and Ecological Relevance of Algae

  • Foundational Role: Cyanobacteria and diatoms (sources of oil/vitamins) are critical to aquatic food chains.
  • Diatomaceous Earth: Fossilized diatom remains used in filtration, polishes, toothpaste, and reflective paint.
  • Algin: Derived from brown algae/kelp. Used in ice cream, salad dressing, latex paint, textiles, and ceramics to regulate water and ice crystal size.
  • Iodine: Harvested from kelp.
  • Red Algae Uses:
    • Food: Dulse and Nori.
    • Carrageenan: A thickening agent.
    • Agar: Extracted from Gelidium; used to solidify culture media, retain moisture in baked goods, and in cosmetics.

Slime Molds (Myxomycota and Dictyosteliomycota)

  • Myxomycota (Plasmodial Slime Molds):

    • Lack chlorophyll; feed on bacteria.
    • Plasmodium: A naked mass of protoplasm with many diploid nuclei.
    • Replication: Convers into sporangia containing spores held in a network of threads called capillitium.
    • Sexual Cycle: Spores undergo meiosis and grow into myxamoebae (gametes) that fuse to form zygotes.

  • Dictyosteliomycota (Cellular Slime Molds):

    • Individual amoeba-like cells clump to form a pseudoplasmodium (slug-like mass) which transforms into a sporangium-like mass of spores.
    • Ecological Role: Decomposers of organic particles.

Phylum Oomycota — The Water Molds

  • Appearance and Structure: Cottony growths on fish/insects; range from single cells to branching coenocytic hyphae (lacking cross-walls). Masses are called mycelia.
  • Affinities with Brown Algae: Shared traits include oogamy, cellulose walls, diploid lifecycle, and biflagellated zoospores.
  • Reproduction: Asexual via zoospores at hyphae tips; sexual via meiosis in oogonia/antheridia.
  • Historical Impact: Responsible for downy mildew on grapes and the potato blight leading to the Irish Potato Famine of 18461846.