Protists

Chapter 29

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Protists

Protists are the most diverse of the four eukaryotic kingdoms

-Unicellular, colonial and multicellular groups

The kingdom Protista is paraphyletic

Some protists are surrounded by Extracellular Material deposited outside of the plasma membrane

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Protists-The 15 major protist phyla are grouped into seven major monophyletic groups-However, 60 lineages cannot be placed with confidence

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Protists

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Eukaryotic Origins

Eukaryotic cells differ from prokaryotes by the presence of a cytoskeleton and organelles

Appearance of eukaryotes in microfossils occurred about 1.5 BYA

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Eukaryotic Origins

The nucleus and endoplasmic reticulum arose from infoldings of prokaryotic cell membrane

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Many organelles evolved via

endosymbiosis between an

ancestral eukaryote and a

bacterial cell

Over time, most organellar genes moved into the nucleus

-Therefore, these organelles cannot be grown in pure culture

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Secondary endosymbiosis -Red and green algae engulfed cyanobacteria-Brown algae engulfed red algae

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General Biology of the Protists

Nutrition

-Phototrophs

-Heterotrophs

-Phagotrophs – Particulate food matter

-Osmotrophs – Soluble food matter

-Mixotrophs are both phototrophic and heterotrophic

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General Biology of the Protists

Asexual reproduction

-Typical mode of reproduction

-Some species have an unusual mitosis

-Binary fission = Equal cells

-Budding = Progeny cell smaller

-Schizogony = Multiple fission

Sexual reproduction

-Union of haploid gametes which are produced by meiosis

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Diplomonads and Parabasalids -Are closely related to the early, now extinct

eukaryotic cell

-Flagellated-Lack mitochondria

Diplomonads-Have two nuclei-Giardia intestinalis Parabasalids

-Have undulating membranes

-Trichomonas vaginalis

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EuglenozoaEuglenoids were among the earliest

eukaryotes to possess mitochondria

-1/3rd have chloroplasts-All have a flexible pellicle

-Stigma – Movement towards light

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Euglenozoa

Kinetoplastids-Unique, single mitochondrion with 2 types of DNA maxicircles and minicircles (expressed genes are used in RNA editing and glycolysis)-Trypanosomes cause human diseases

-African sleeping sickness – Tsetse fly-Escapes immune systems because only one

of 1000-2000 variable antigen genes is expressed at a time on the glycoprotein coat

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Alveolata

Alveolata have flattened vesicles called alveoli

-These function like Golgi bodies below the cell membrane

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AlveolataDinoflagellates

-Unicellular with two unequal flagella-Live in aquatic environments

-Most are photosynthetic

-Reproduction is primarily asexual

-About 20 species produce powerful toxins that harm vertebrates...“Blooms” are responsible for red tide--kills marine vertebrates

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Alveolata Apicomplexans (Spore-forming animal parasites) Plasmodium

-An apicomplexan that causes malaria -Organism has a very complex life cycle

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Alveolata

Ciliates Paramecium-Have two types of nuclei-Macronucleus = Divides by mitosis

-Responsible for physiological functions-Micronucleus = Divides by meiosis

-Involved in conjugation-Fusion of two cells of different

mating types

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Paramecium

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-Food vacuoles = Digestion of food

-Contractile vacuoles = Regulation of water

balance

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Stramenopila

Stramenopiles have very fine hairs on their flagella-A few species have lost their hairs during evolution

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Stramenopila

Brown algae

-Kelps

-Grow in relatively shallow waters throughout the world-Life cycle involves alternation of generations

-Sporophyte = Multicellular and diploid

-Gametophyte = Multicellular and haploid

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StramenopilaDiatoms (Phylum Chrysophyta)

-Unicellular organisms

-Have unique double shells made of opaline silica

-Some move using raphes--lined with vibrating fibrils

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Rhodophyta

Rhodophyta, or red algae, range from microscopic to

very large sizes

-Have accessory photosynthetic pigments within

phycobilisomes

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Choanoflagellida

Choanoflagellates are most like the common ancestor of all animals

-Single emergent flagellum, surrounded by funnel-shaped contractile collar

-Use collar to feed on bacteria

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Protists Without a Clade

Amoebas are paraphyletic

-Rhizopoda (True amoebas) -Move by means of cytoplasmic

projections called pseudopods

-Actinopoda (Radiolarians) -Glassy exoskeletons made of

silica-Needlelike pseudopods

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Protists Without a CladeForaminifera are heterotrophic marine protists

-Have pore-studded shells called tests, through which thin podia emerge (for swimming and feeding)

-Have complex life cycles with haploid and diploid generations

-Limestones

are rich in forams

-White cliffs

of Dover

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Slime molds w/o a clade1. Plasmodial slime molds

-Stream along as a plasmodium, a nonwalled, multinucleate mass of cytoplasm

-Ingests bacteria and other organic material

-When food or moisture is scarce, organism forms sporangia, where spores are produced

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2. Cellular slime molds

-Individual organisms behave as separate amoebas

-Move through soil ingesting bacteria

-When food is scarce, organisms aggregate to form a moving slug

-Slug differentiates into a sorocarp with spores that differentiate into amoebas again

Slime molds w/o a clade