Chapter 23: Protists Flashcards
What defines protists as a group?
Eukaryotic organisms (have membrane-bound organelles).
Mostly unicellular, but some are colonial or multicellular (e.g., algae).
Nutritionally diverse: Autotrophs (photosynthetic algae), heterotrophs (protozoa), or mixotrophs (e.g., Euglena).
Found in aquatic environments, moist soil, or as parasites/symbionts.
Paraphyletic group: Do not share a single common ancestor, making classification complex.
Explain the endosymbiotic origin of eukaryotes and its relevance to protists.
Primary endosymbiosis: An ancestral archaeon engulfed aerobic bacteria (becoming mitochondria) and photosynthetic cyanobacteria (becoming chloroplasts). These organelles retained their own DNA.
Secondary endosymbiosis: Eukaryotes engulfed other eukaryotes with chloroplasts (e.g., red/green algae), leading to chloroplasts with 3–4 membranes (e.g., Euglena).
Significance: Explains the diversity of plastids and mitochondria in protists.
List the six supergroups of protists and their defining traits.
Excavata: Feeding groove, modified mitochondria (e.g., Giardia).
Chromalveolata: Alveoli (membrane sacs); includes dinoflagellates, ciliates, and diatoms.
Rhizaria: Thin, threadlike pseudopodia (e.g., Foraminiferans).
Archaeplastida: Descendants of primary endosymbiosis (red/green algae, land plants).
Amoebozoa: Lobe-shaped pseudopodia (e.g., Amoeba, slime molds).
Opisthokonta: Includes animals, fungi, and choanoflagellates.
Describe Excavata subgroups with examples.
Euglenozoans:
Euglena: Mixotrophic, uses flagella, has an eyespot.
Trypanosoma: Parasitic; causes African sleeping sickness.
Diplomonads:
Giardia: Lacks mitochondria, causes giardiasis.
Parabasalids:
Trichomonas vaginalis: Parasitic in the human urogenital tract.
What are alveolates? Name subgroups and examples.
Alveolates (supergroup Chromalveolata) have alveoli (membrane sacs beneath the plasma membrane). Subgroups:
Dinoflagellates:
Marine plankton; some bioluminescent (e.g., Noctiluca).
Cause red tides (e.g., Karenia brevis).
Apicomplexans:
Parasites with apical complex for host invasion (e.g., Plasmodium causing malaria).
Ciliates:
Use cilia for movement (e.g., Paramecium).
Compare red algae, green algae, and brown algae.
Trait Red Algae (Rhodophyta) Green Algae (Chlorophyta) Brown Algae (Phaeophyta)
Pigments Phycoerythrin (red) Chlorophyll a/b Fucoxanthin (brown)
Habitat Deep marine waters Freshwater/marine Cold marine (kelp forests)
Structure Multicellular Unicellular or multicellular Multicellular (e.g., kelp)
Example Porphyra (nori) Volvox, Ulva Macrocystis (giant kelp)
What are diatoms? Why are they ecologically important?
Unicellular Chromalveolates with silica cell walls (intricate glass-like patterns).
Ecological roles:
Produce ~20% of Earth’s oxygen via photosynthesis.
Base of aquatic food chains.
Fossilized remains form diatomaceous earth (used in filters, toothpaste).
How do slime molds differ from fungi?
Slime molds (Amoebozoa):
Move via amoeboid motion (plasmodial or cellular forms).
Absorb nutrients via phagocytosis (unlike fungi, which absorb externally).
Example: Physarum (plasmodial), Dictyostelium (cellular).
Fungi: Chitin cell walls, reproduce via spores, and are opisthokonts.
Explain the life cycle of Plasmodium (malaria parasite).
Mosquito phase: Sexual reproduction in Anopheles mosquito gut.
Human phase:
Sporozoites infect liver cells → asexual reproduction (merozoites).
Merozoites infect red blood cells → cause cyclic fevers.
Gametocytes form, ingested by mosquitoes to restart cycle.
What are Rhizaria? Provide examples and their significance.
Protists with threadlike pseudopodia (e.g., Foraminiferans, Radiolarians).
Foraminiferans:
Calcium carbonate shells; fossilize into limestone/chalk (e.g., White Cliffs of Dover).
Radiolarians:
Silica shells; form sedimentary oozes used in paleoclimate studies.
Describe mixotrophy in protists. Give an example.
Mixotrophy: Combining photosynthesis (autotrophy) and heterotrophy (e.g., engulfing prey).
Example: Euglena
Uses chloroplasts for photosynthesis in light.
Engulfs organic matter in darkness.
How do protists contribute to symbiotic relationships?
Coral symbiosis: Zooxanthellae (dinoflagellates) provide corals with sugars via photosynthesis.
Lichen: Algae (protists) + fungi.
Termite gut symbionts: Trichonympha (Excavata) digest cellulose for termites.
What human diseases are caused by protists?
Disease Protist Transmission
Malaria Plasmodium spp. Anopheles mosquito bite
Amoebic dysentery Entamoeba histolytica Contaminated water/food
Toxoplasmosis Toxoplasma gondii Cat feces, undercooked meat
African sleeping sickness Trypanosoma brucei Tsetse fly bite
What is alternation of generations in algae?
Life cycle alternating between haploid gametophyte and diploid sporophyte stages.
Example: Kelp (brown algae)
Sporophyte (large, diploid) produces spores → develop into gametophytes (tiny, haploid).
Gametophytes produce gametes → fuse to form new sporophytes.
Why are foraminiferan fossils important in geology?
Their calcium carbonate shells accumulate as limestone/chalk.
Used to date rock layers (biostratigraphy) and reconstruct past ocean conditions (e.g., temperature, salinity).
