Chapter 28: Protists Flashcards
Protist
- Mostly unicellular group of eukaryotes informally known as protists
- Most eukaryotes are singe-celled organisms
Structural and Functional Diversity
- Most protists are unicellular, however some colonial and multicellular
- Diverse in nutrition
- Diversity thought to have arisen from endosymbiosis
Mixotroph
Combines photosynthesis with heterotrophic nutrition
Endosymbiosis
Relationship between two species in which one organism lives inside the cell or cells of another organism
Secondary endosymbiosis
- Protist was ingested in food vacuoles of heterotrophic eukaryotes and became endosymbionts themselves
Diplomonads
Reduced mitochondria called mitoses; organelles lack functional electrons transport chains; many are parasites
Parabasalids
- Reduced mitochondria; generate some energy anaerobically
- Example is T. vaginalis
Euglenozoans
Belong to diverse clade that includes predatory heterotrophs, photosynthetic autotrophs, mixotrophs, and parasites; presence of rod with either spiral or crystalline structure inside each of their flagella
Kinetoplastids
- Single, large mitochondrion that contains organized mass of DNA called kinetoplast; feed on prokaryotes in freshwater, marine, moist terrestrial ecosystems
- Trypanosoma (sleeping sickness–evade immune system quite easily)
Bait-and-Switch
- Surface coated with millions of single protein; immune system can recognize these
- New generation of parasite switches to another surface protein with different molecular structure
- Prevents host from obtaining immunity
“SAR” Clade
- Proposed based on whole genome DNA sequence analyses
- Stramenopiles, alveolate, and rhizarians to form a monophyletic supergroup
Stramenopiles
- Important photosynthetic organisms
- Name refer to characteristic flagellum with numerous fine, hairlike projections
- Three groups: diatoms, golden algae, and brown algae
Diatoms
- Unicellular algae that have unique glass-like wall made of silicon dioxide embedded in organic matrix
- Can withstand immense amounts of pressure
- Highly diverse and populated
Golden Algae
- Color results from yellow/brown carotenoids
- Cells are biflagellate (both flagella attached near one end of cell)
Brown Algae
- Multicellular; most are marine
- Common along temperate coasts
- Holdfast: Rootlike anchor
- Stripe: Supports leaflike blades
- Analogous to plants
Alternation of Generations
- Alternation of haploid and diploid forms
- Present in brown algae
- Haploid form –> Releases male and female gametes –> Gametes recombine to form haploid form again
- Isomorphic: Sporophytes and gametophytes look similar to each other
- Heteromorphic: Sporophytes and gametophytes are structurally different
Alveolates
- Membrane-enclosed sacs just under the plasma membrane
- Abundant in many habitats and include wide range of photosynthetic/heterotrophic protists
Dinoflagellates
- Reinforced by cellulose plates; flagella located in grooves in armor and spin to propel
- Important species include plankton, photosynthetic bacteria
- Blooms: May create “red tide,” toxins produced capable of killing invertebrates and fishes
Apicomplexans
- Parasites of animals; attack virtually all animal species
- Plasmodium: In humans, reproduce in liver and emerge in blood cells before bursting (alternation of generations occurs here too )
Ciliates
- Large/varied group of protists named for their use of cilia to move and feed
- Genetic variation is induced by conjugation (two individuals exchange haploid micronuclei but do not reproduce)
Rhizarians
- Many are amoebas, some radiolarian, forams, cercozoans
Amoebas
Move about by means of pseudopodia (extension that bulges from anywhere on cell surface )
Radiolarians
- Delicate, intricately symmetrical internal skeleton made of silica
- Pseudopodia radiate from central body, reinforced by microtubules
Forams
- Foraminiferans are named for porous shells (tests); consist of single piece of organic material hardened with calcium carbonate
- 90% of all identified species are known from fossils
Cercozoans
- Large group of amoeboid and flagellated protists that feed using threadlike pseudopodia; common inhabitants of marine, freshwater, and soil ecosystems
Closest relatives of land plants
- Red and green algae
Archaeplastida
- Monophyletic group that descended from ancient protist that engulfed a cyanobacterium
Red Algae
- Reddish owing to photosynthetic pigment called phycoerythrin; most abundant large algae in warm coastal waters of tropical oceans
- Most multicellular
- Reproduce sexually; diverse life cycles with alternation of generations
Green Algae
- Structure and pigment composition much like chloroplasts of land plants
- Divided into charophytes and chlorophytes
- Grass green chloroplasts
Charophytes
- Algae most related to land plants
Chlorophytes
- Include more than 7,000 species
- Various species live independently in aquatic habitats
- 3 Different Mechanisms: Formation of colonies of individual cells, formation of true multicellular bodies by cell division and differentiation, and repeated division of nuclei without cytoplasmic division
Life Cycle of Chlamydomonas
- Mature cells are haploid and contain single cup-shaped chloroplast
- Respond to nutrient shortage by developing into gametes
- Gametes fuse to form diploid zygote
- Fertilization occurs, forms zygote
- Meiosis produces four haploid individuals that emerge and mature
- Asexual reproduction can occur; daughter cells develop flagella and cell walls and emerge as swimming zoospores
Unikonta
- Extremely diverse supergroup of eukaryotes that includes animals, fungi, and some protists
- Two major kinds: Amoebooans and ophisthokonts
Amoebozoans
- Includes species of amoebas hat have lob- or tube-shaped pseudopodia
- Slime mold
- Tubulinds
- Entamoebas
Opisthokonts
- Highly variable
- Include choanoflagellates, nucleariids, animals, fungi
Protists’ Role in Ecological Communities
- Most protists are aquatic but can be found anywhere
- Symbiotic protists (termite guts dissolve cellulose), parasites that have compromised economies of other countries (malaria)
- Photosynthetic protists (producers)
- Constitute roughly 50% of world’s photosynthesis
