General Biology of Protists

General Biology of Protists

Slime molds obtain nutrition by

Plasmodial and cellular slime molds belonging to Amoebozoa acquire nutrients not through osmotrophic absorption like fungi secreting extracellular enzymes, but via phagocytic ingestion resembling amoebae. Multinucleate plasmodium migrates along substrates streaming cytoplasm rhythmically engulfing bacterial cells, yeast spores, and detritus forming food vacuoles where lysosomal enzymes digest prey intracellularly. Lack of cell wall in trophic stage facilitates engulfment. Presence of fruiting bodies superficially resembles fungal sporangia, yet feeding mode relies on endocytosis and actin based engulfment, aligning slime molds nutritionally with protozoa rather than absorptive fungal kingdom.

Ref: Stephenson Myxomycetes phagocytosis ingestion; Campbell Biology Chapter 28 Slime molds ingestion endocytosis not absorption osmotrophy

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General Biology of Protists

Foraminiferans have shells made of

Foraminifera, amoeboid members of Rhizaria supergroup, construct elaborate tests or shells primarily composed of calcium carbonate secreted as calcite or aragonite, sometimes agglutinating foreign particles with organic cement, ranging from single chamber to multichambered spiral morphology. Reticulopodia extend through apertures for prey capture and locomotion. Tests accumulate as pelagic oozes forming chalk deposits, significant in marine carbon sequestration. Fossil assemblages enable paleoceanographic reconstruction and biostratigraphic dating due to abundance. Chemistry differs from siliceous skeletons of radiolaria and diatoms, reflecting distinct biomineralization pathways using calcium ATPases and carbonic anhydrase.

Ref: Hemleben et al., Foraminifera shells calcium carbonate; OpenStax Biology Foraminiferans calcite tests paleontology carbon cycle

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General Biology of Protists

Ciliates possess

Ciliate protists within phylum Ciliophora exhibit distinctive nuclear dimorphism possessing two types of nuclei within single cell: large polyploid somatic macronucleus containing highly amplified fragmented chromosomes actively transcribing genes regulating vegetative growth, metabolism, and asexual fission, and small diploid germline micronucleus transcriptionally inert during vegetative stage but undergoing meiosis during sexual conjugation. Post-conjugation new macronucleus differentiates from micronucleus through extensive programmed genome rearrangement including chromosome fragmentation and elimination. This dual organization underpins phenotypic plasticity and genetic exchange in Paramecium, Tetrahymena, and Stentor.

Ref: Tortora Microbiology Ciliophora nuclear dimorphism; Campbell Biology 12th ed., Chapter 28 Ciliates macro- micronuclei dimorphism conjugation

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General Biology of Protists

Plasmodium completes sexual reproduction in

Plasmodium species causing malaria exhibit heteroxenous life cycle requiring vertebrate intermediate host and invertebrate definitive host. Asexual schizogony occurs in human liver and erythrocytes causing disease manifestations. Sexual phase begins with gametocyte formation ingested during blood meal by female Anopheles mosquito; within midgut gametes fuse forming diploid zygote developing into motile ookinete penetrating epithelium forming oocyst undergoing sporogony producing haploid sporozoites migrating to salivary glands for reinfection. Fertilization and meiosis completion occurs in mosquito, establishing it as definitive host where sexual reproduction culminates.

Ref: CDC Malaria sexual reproduction Anopheles mosquito; Tortora life cycle Plasmodium definitive host female Anopheles sporogony

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General Biology of Protists

Apicomplexans are characterized by

Phylum Apicomplexa comprises obligate intracellular parasitic alveolates defined by anterior apical complex ultrastructure visible in electron microscopy consisting of conoid, paired rhoptries secreting adhesins, micronemes for recognition, and dense granules modifying parasitophorous vacuole. Complex mediates sequential attachment, reorientation, formation of moving junction, and active invasion of host cells without triggering endocytosis. Includes genera Plasmodium, Toxoplasma, Cryptosporidium, and Eimeria. Presence of remnant plastid apicoplast derived from secondary endosymbiosis and alveoli sacs distinguishes apicomplexans from other protists, providing therapeutic targets for antiparasitic drugs.

Ref: Levine Apicomplexa apical complex rhoptries micronemes; Campbell Biology 11th ed., Chapter 28 Apicomplexans invasion organelles conoid

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General Biology of Protists

Dinoflagellates often cause

Dinoflagellates, flagellate alveolates bearing two dimorphic flagella within transverse and longitudinal grooves, can proliferate exponentially forming harmful algal blooms termed red tides due to peridinin carotenoid and high cell densities imparting reddish brown discoloration to seawater. Nutrient enrichment, stratification, and temperature favor blooms, some species produce potent neurotoxins saxitoxin, brevetoxin causing paralytic shellfish poisoning, neurotoxic shellfish poisoning, and massive fish kills detrimental to fisheries. Bioluminescent blooms also occur. Mechanism differs from green tides caused by Ulva and golden tides by Sargassum reflecting dinoflagellate ecology.

Ref: Smayda Dinoflagellate blooms red tides cause; Campbell Biology 11th ed., Chapter 28 Dinoflagellates harmful algal blooms peridinin toxins

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General Biology of Protists

Oomycetes differ from fungi because they have

Brown algae Phaeophyceae within stramenopiles display olive-brown hue due to dominance of accessory light harvesting carotenoid fucoxanthin over chlorophyll a, chlorophyll c1 and c2, and beta-carotene pigments. Fucoxanthin bound to fucoxanthin-chlorophyll a/c protein complexes absorbs blue-green light 450 to 540 nanometers abundant at moderate depths, efficiently transferring excitation to chlorophyll a for photosynthesis. Pigment composition masks green chlorophyll, conferring characteristic coloration to kelps, rockweeds, and Sargassum. Unlike phycoerythrin providing red coloration in red algae and phycocyanin blue in cyanobacteria, fucoxanthin pigment defines brown algal ecological niche.

Ref: Alexopoulos Introductory Mycology Oomycetes cellulose wall not chitin; Campbell Biology 11th ed., Chapter 31 Oomycetes differ fungi cellulose glucan

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General Biology of Protists

Brown algae color is due to

Brown algae Phaeophyceae within stramenopiles display olive-brown hue due to dominance of accessory light harvesting carotenoid fucoxanthin over chlorophyll a, chlorophyll c1 and c2, and beta-carotene. Fucoxanthin bound to fucoxanthin-chlorophyll a/c protein complexes absorbs blue-green light 450 to 540 nanometers abundant at moderate depths, efficiently transferring excitation to chlorophyll a for photosynthesis. Pigment composition masks green chlorophyll, conferring characteristic coloration to kelps, rockweeds, and Sargassum. Unlike phycoerythrin providing red coloration in red algae and phycocyanin blue in cyanobacteria, fucoxanthin defines brown algal lineage.

Ref: Lee Phycology 5th ed., Brown algae fucoxanthin; Campbell Biology 12th ed., Chapter 28 Stramenopiles brown algae pigments light harvesting

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General Biology of Protists

Diatom cell wall is made of

Diatoms within stramenopile lineage secrete elaborate box-like cell wall termed frustule composed predominantly of hydrated amorphous silica polymerized as opal SiO2·nH2O, comprising two overlapping halves epitheca and hypotheca with intricate perforations, ribs, and spines visualized in scanning electron microscopy. Silicic acid uptake via SIT transporters and deposition in silica deposition vesicle mediated by silaffins and long-chain polyamines guides patterning. Frustule provides mechanical protection against grazing, contributes to rapid sinking and fossilization forming diatomaceous earth. Chemistry distinguishes diatoms from cellulose, chitin, or carbonate walled organisms.

Ref: Round et al., Diatoms Biology Morphology silica frustule; Campbell Biology 11th ed., Chapter 28 Diatom cell wall silica deposition

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General Biology of Protists

SAR clade includes

SAR acronym denotes monophyletic megaassembly of three major protistan groups confirmed by multigene phylogenomic analyses and shared rare genomic characters: Stramenopiles also called heterokonts possessing tripartite tubular hairs on longer flagellum, Alveolates possessing cortical alveoli beneath plasma membrane, and Rhizaria extending filose pseudopodia for feeding and test formation. Stramenopiles include diatoms, brown algae, oomycetes; Alveolates include ciliates, apicomplexans, dinoflagellates; Rhizaria include foraminifera, radiolaria, cercozoans. Together SAR comprises greater than half of protist diversity, dominating marine plankton and benthic ecosystems ecologically and functionally.

Ref: Burki et al. 2008 SAR clade Stramenopiles Alveolates Rhizarians; Adl et al. 2012 protist classification SAR supergroup monophyletic

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General Biology of Protists

Kinetoplast is associated with

Kinetoplast refers to conspicuous electron-dense structure located within single giant mitochondrion positioned near basal body in kinetoplastid protists, representing massive network of concatenated circular DNA molecules comprising dozens of maxicircles encoding respiratory proteins and thousands of minicircles encoding guide RNAs directing uridine insertion-deletion editing. Replicated synchronously with cell division via tripartite attachment complex linking kDNA to flagellum. Phylogenetically distinctive to Kinetoplastea including Trypanosoma and Leishmania, kinetoplast organization differs from conventional punctate nucleoids, providing diagnostic trait and target for antitrypanosomal drugs interfering with mitochondrial replication.

Ref: Shapiro Englund Annu Rev Microbiol kinetoplast mitochondrial DNA network; Campbell Biology Chapter 28 Kinetoplast kDNA maxicircles minicircles

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General Biology of Protists

Trypanosoma belongs to

Trypanosoma genus encompassing Trypanosoma brucei causing African sleeping sickness and Trypanosoma cruzi causing Chagas disease represents parasitic kinetoplastid flagellates within class Kinetoplastea of Excavata. Cells possess single emergent flagellum originating from flagellar pocket near posterior kinetoplast, attached to cell body via undulating membrane generating propulsive waves. Life cycles involve insect vectors tsetse flies and triatomine bugs with antigenic variation. Unlike euglenoids bearing photoreceptive stigma and chloroplasts in some species, trypanosomes are strictly heterotrophic blood parasites exhibiting unique mitochondrial RNA editing and polycistronic transcription.

Ref: CDC DPDx Trypanosomiasis Trypanosoma kinetoplastid; Jawetz Medical Microbiology Trypanosoma single flagellum undulating membrane

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