Protists (Not Final Material) Flashcards
Archaeplastida
A significant photosynthetic supergroup of eukaryotes including red algae, green algae, and plants
Red Algae
distinguished by their reddish coloration attributed to the photosynthetic accessory pigment phycoerythrin, are predominantly multicellular marine
seaweeds.
Green Algae
Derive their name from the green chlorophyll pigments present in their chloroplasts (chlor = green).
Green algae, which excludes plants, encompasses a paraphyletic assemblage including chlorophytes and charophytes.
- Charophytes are the sister taxon of plants
- Green algae include unicellular, colonial, and multicellular forms (seaweeds)
- The life cycles of green algae are often complex, involving both sexual and asexual reproductive stages
Green algae exhibit diverse habitat preferences, with many species inhabiting freshwater, while others thrive in marine habitats, damp soil, or snow.
- Some green algae form symbiotic relationships with other organisms, such as fungi, to create lichens
Unikonta
Supergroup Unikonta includes heterotrophic protists closely related to fungi and animals.
- It comprises two main clades:
- Amoebozoans
- Opisthokonts, which include animals, fungi, and various protist groups
Most unikonta protists either possess a single emergent flagellum or are amoebae devoid of flagella.
Amoebozoans
Amoebozoans are a diverse array of amoeba
Characterized by:
- lobe or tube shaped pseudopodia distinct from the threadlike pseudopodia in other groups
- Their flexible body shape facilitates movement through the extension of blunt lobes (pseudopodia), and they feed via phagocytosis, engulfing particles for nutrition.
Primarily unicellular
- certain amoebozoans form multicellular structures through the aggregation of amoeba-like cells.
Includes:
- Slime moulds
- Tubulimids
- Entamoebas
Amoebozoan Slime Moulds
Although amoebozoan slime moulds were initially misclassified as fungi, molecular systematics repositioned them within the amoebozoa.
- The resemblance between slime moulds and fungi is a result of convergent evolution.
- Two main lineages exist within slime moulds: plasmodial slime moulds and cellular slime moulds
What are the three major types of Amoebozoans
- Slime Moulds
- Tubulinids
- Entamoebas
Plasmodium (the structure, not the genus)
plasmodium - a large mass encased in a single membrane containing numerous diploid nuclei.
- Formin in plasmodial slime moulds
Plasmodial slime moulds
Type of amoebozoan slime mould
Plasmodial slime moulds, often brightly pigmented, form a large mass called a plasmodium, encased in a single membrane containing numerous diploid nuclei.
- The plasmodium is a multinucleate mass (“supercell”).
- Extending pseudopodia through decaying material, they engulf food via phagocytosis.
Cellular Slime Moulds
A type of Amoebozoan slime mould
Cellular slime moulds form multicellular aggregates, maintaining cellular separation through membranes
- Cellular slime moulds spend most of their lives feeding as individual unicellular amoebas but can aggregate to form a fruiting body.
Tubulinids
Subgroup of Amoebozoan
Tubulinids, another diverse subgroup of amoebozoans, exhibit lobe- or tube-shaped pseudopodia and are commonly found in soil, freshwater, and marine environments.
- Predominantly bacterivorous, they actively seek and consume bacteria and other protists
Entamoebas
Subgroup of Amoebozoan
Entamoebas are pseudopodia-forming, intestinal parasites causing diseases like amebic dysentery, a significant global health concern.
- Amebic dysentery, caused by Entamoeba histolytica, spreads through fecal contamination of food and water, affecting millions worldwide.
Rhizarians
Rhizarians are a diverse group of primarily unicellular protists defined by genetic similarities rather than shared morphological traits.
- Lack overall characteristics
- Most rhizarians are amoebas
- Amoebas within the rhizarian clade are distinguished by their threadlike pseudopodia
- Heterotrophs
- Many rhizarians engage in endosymbiotic associations with unicellular marine algae, enabling them to adopt mixotrophic lifestyles.
Alveolates
Subgroup of the SAR Clade
Members of clade Alveolata are distinguished by the presence of membrane-bound sacs known as alveoli
- Alveoli create a continuous, flattened layer beneath the plasma membrane, providing structural support and often forming a flexible ‘skin’.
- Alveolates include dinoflagellates, apicomplexans, and ciliates.
What are the major types of Alveolates?
Alveolates include dinoflagellates, apicomplexans, and ciliates
Dinoflagellates
Dinoflagellates, characterized by two flagella, possess alveoli that support overlapping cellulose plates
- comprises aquatic organisms exhibiting various modes of nutrition, including photoautotrophy, chemoheterotrophy, and mixotrophy.
Habitat:
Dinoflagellates are prolific in both marine and freshwater ecosystems and are frequently responsible for toxic ‘red tides’ during blooms.
Ciliates
Ciliates, a diverse group of alveolates, utilize cilia for locomotion and feeding, e.g. Paramecium.
- Ciliates are heterotrophic: many freeliving ciliate species feed on bacteria and smaller protists through phagocytosis (phagos = eat, cyto = cell).
- While asexual reproduction via binary fission is common among ciliates, genetic diversity arises from conjugation, wherein individuals exchange haploid micronuclei
Ampicomplexans
Subgroup of the Alveolates
Apicomplexans are primarily parasites of animals, including species that pose significant threats to human health.
- These parasites propagate through infectious cells known as sporozoites, featuring an apex specialized for penetrating host cells and tissues.
- Most apicomplexans exhibit complex life cycles involving sexual and asexual stages and multiple host species
Example:
The apicomplexan Plasmodium parasite is responsible for malaria transmission, requiring both mosquitoes and humans to complete its life cycle.
SAR clade
The SAR clade represents a highly diverse monophyletic supergroup of protists, characterized by similarities in DNA sequences.
- Dominates eukaryotic diveresity in acean ecosystems
The SAR clade is named after its three major nested clades:
- Stramenopiles
- Alveolates
- Rhizarians
Believed to have originated through secondary (2°) endosymbiosis
- non-photosynthetic eukaryote eats read alga
Stramenopiles
SAR Clade
The stramenopiles clade includes some of Earth’s most significant photosynthetic organisms
- diatoms
- brown algae
- non-photosynthetic oomycetes.
Diatoms
A subgroup of Stramenopile
Highly diverse unicellular algae that are major components of marine phytoplankton
- Responsible for generating approximately 20-50% of global oxygen production.
- Possess a unique two-part, glass-like cell wall made of silica (hydrated silicon dioxide) and typically reproduce asexually, occasionally engaging in sexual reproduction.
- Important contributors to oceanic carbon sequestration.
Brown Algae
Subgroup of stamenopiles
The largest and most complex algae, are primarily multicellular marine species known as “seaweeds”.
- They dominate temperate and polar oceans, with giant seaweeds called kelps inhabiting deep oceanic regions.
- Although plant-like in appearance, brown algae lack true roots, stems, and leaves, exhibiting broad morphological similarities to plants as examples of analogous structures.
- The cell walls of brown algae consist of the polysaccharides cellulose and alginic acid.
Life cycle of brown algae
The life cycle of most brown algae involves alternation of generations, transitioning between multicellular haploid (1n) and diploid (2n) forms.
- Sporophyte stage: The diploid sporophyte produces haploid flagellated spores known as zoospores, each equipped with paired “hairy” and “smooth” flagella.
- Gametophyte stage: zoospores develop into haploid male and female gametophytes, which in turn produce gametes through mitosis.
- Fertilization and zygote formation: Fertilization occurs when gametes from male and female gametophytes fuse, resulting in the formation of a diploid zygote.
Oomycetes
Subgroup of Stramenopiles
Filamentous, heterotrophic stramenopiles, including water moulds, white rusts, and downy mildews.
- Formerly classified as fungi due to their filamentous morphology, molecular systematics have confirmed their placement within the stramenopiles clade, distinct from fungi
- Cellulose cell walls
Habitat and Ecological Role:
Oomycetes are often found in water or damp environments where they function as decomposers or they can be pathogens of plants, animals, and other organisms
Clade Excavata
Clade Excavata includes protists with mitochondria or distinctive flagella.
- Unicellular
- Exhibit multiple lifestyles
- Free living or Symbiotic
- Predatory or Phosynthetic
- Lack unifying set of cytoskeletal structures
Divided into 3 clades
- Diplamonads
- Parabasalids
- Euglenozoans
Diplomonads and Parabasalids
Clade Excavata
Diplomonads and Parabasalids are unicellular, heterotrophic flagellates with distinct features
Diplomonads lack plastids and typically inhabit anaerobic environments, relying on anaerobic processes for energy.
- Many are parasitic
Parabasalids also lack plastids and have modified mitochondria.
- Commonly found in anaerobic environments
- One causes vaginal infections
Euglenozoans
Euglenozoans are a diverse clade, including various organisms with varied ecological roles
- Euglenozoan clade includes predatory heterotrophs, photoautotrophs, and parasites, demonstrating its diversity in ecological strategies.
- A distinguishing feature of this group is the presence of spiral or crystalline rods of unknown function inside their flagella (Fig 28.7).
Subgroups: Kinetoplastids and Euglenids.
What are the two subgroups of Euglenozoans
Kinetoplastids - have a single mitochondrion containing a large mass of DNA known as a kinetoplast.
- Includes free-living species functioning as heterotrophic consumers in freshwater, marine, and moist terrestrial ecosystems.
- Certain species are parasitic, such as Trypanosoma, which causes sleeping sickness in humans.
Euglenids - characterized by one or two flagella emerging from a pocket at one end of the cell.
- Some species exhibit a mixotrophic lifestyle, functioning as both autotrophs and heterotrophs concurrently.
What are the 4 major subgroups of Eukaryotes?
- Excavata
- SAR
- Archaeplastida (includes plants)
- Unikonta (includes fungi and animals)
