CHAPTER 28 : Protists The Protists represents an unusual mix of organisms. Protists are more diverse than all other eukaryotes and are no longer considered a single kingdom - The organisms found in this are all eukaryotes and most are single-celled for most of their life-cycle however but some are colonial and there may even be multicellular forms. Remember the eukaryotic differences:- Nucleus (with a double membrane)- Organelles- 2 or more chromosomes (DNA + proteins)Since the Protista are eukaryotic cells, they are clearly different from the Bacteria and Archaea.- The differences between the protists and the rest of the eukaryotes are not quite as clear. Protists are nutritionally diverse and can be organized them into general groups based on nutritional methods:- Autotrophic (photosynthetic) - Heterotrophic (decomposers)- Heterotrophic (ingestion - hunters and symbiotic)Mixotrophic (combining photosynthesis and ingestive or absorptive methods)The evolution of protists is the results of endosymbiosis (see fig. 28.2)1- Primary endosymbiosis resulted in plastid-bearing lineages which evolved into red and green algae.- Secondary endosymbiosis resulted in greater diversification.The current state of what was kingdom Protista is five super groups (see fig 28.3).- Excavates- Chromalveolates- Rhizarians- Archaeplastids- UnikontesExcavates- Move via flagella- Have a feeding groove- Heterotrophic and have modified mitochondriaThe two largest clades of the excavates are the diplomonads and the parabasalidsDiplomonads- both free living and symbiotic species- have two nuclei- multiple flagella- Giardia (see fig 28.3) is a member of this group – infection results from drinks untreated water causing diarrhea etc.Parabasalids- Anaerobic- all known species are symbiotic and some are parasitis- Trichomanas vaginalis (see fig 28.4) is a sexually transmitted member of this group – males can often be asymptomatic.Euglenozoans is a diverse clade in the excavate linage.- have distinctive mitochondria - move via flagella- mixed nutritional methods (i.e mixotrophic)- There are two major groups of euglenozoans, the euglenids and the kinetoplastidsEuglenids o Most are freshwatero Have 1-3 flagellao Primarily photosynthetic but can switch to heterotrophic in the2darko Many lack a rigid cell wallo Have a photoreceptor called an eyespoto Named after Euglena (see fig. 28.7)Kinetoplastidso One flagellumo Single largemitochondriono Both free living andsymbiotic specieso Some of the symbioticspecies are parasitic.Including Trypanosoma (see fig 28.6) - causingsleeping sicknessChromalveolates- This is a large diverse clade which is thought to have arisen by a secondary endosymbiosis of red algae.- Chromalveolates contains two major clades the stramenopiles andthe alveolatesStramenopiles- have many different forms some living as multicellular colonies- varied nutritional methods including mixotrophs- There are three major groups of stramenopiles:o Oomycoteso Diatomso Brown Algaeo Golden AlgaeOomycotes are also called water molds cell walls of cellulose cells can form aggregated colonies filamentous bodies heterotrophic decomposers One common water mold with economic importance is downy mildew.Diatoms May be freshwater or marine Photosynthetic Have glass-like “shells” known as tests (see fig. 28.3) with 3perforation to allow for exchange of substances About 5,600 described living species estimates of 100,000 living species and more than 35,000 extinct species (Based on “shell” morphology)Brown Algae Marine Photosynthetic Deep water to tidal “Brown” color caused by accessory pigments Cell wall has added polysaccharides Cells can form large aggregated multicellular colonies Giant kelp forest Many have gas-bladders to keep the plant extending toward the surface.Golden Algae May be freshwater or marine All are photosynthetic but some species are mixotrophs Flagellated usually with 2 flagella Usually unicellular but may form coloniesAlveolates- most live as single cells- mixed nutritional methods including parasitic forms- varied forms of motility There are three major groups of alveolates:o Dinoflagellateso Apicoplexanso CiliatesDinoflagellates Both marine and freshwater species 2 flagella, one at the end and one in an equatorial groove (see fig 28.9) Some are photosynthetic, many are mixotrophic and many are heterotrophic May have a cellulose cell wall Members of this group are responsible for red tides which result in massive fish kills along the Gulf coast. Apicoplexans (a.k.a – Sporozoans) All are hetrotrophic and most are parasites which have a mobile stage called a Sporozoite. This groups includes:o Plasmodium that causes malaria (see fig 28.10)4o Toxoplasma that vectors through cats. Ciliates Most species are solitary freshwater Hetrotrophic Use cilia for movement and feedingo Cilia are short hair-like filaments that are made of protein. These cilia may be a uniform covering of the organism or can be localized in patches. The ciliates are the most complex of the protists with an internal structure that includes an oral groove, an anal pore, a contractile vacuole and two types of nuclei. (See fig. 28.11a) These two different nuclei have different functions: o The macronucleus handles all the day-to-day businesso the micronucleus functions in sexual reproduction or conjugation (see fig 28.11b) Rhizarians- most live as single cells- most are hetrotrophic but some mixotrophic species are present- motility based on very thin pseudopodia - may be reclassified as a clade within the Chromalveolates- The rhizarians includes o Foraminiferans o Radiolarians o Cercozoans o Foraminiferans or forams both marine and freshwater species external multichambered shell known as tests composed of CaCO3 many species characterized based on shell morphology pseudopodia extend through pores in the shellRadiolarians- mainly marine- internal skeleton-like shell composed of silica (glass)- many species characterized based on shell morphology (seefig 28.18).Cercozoans- very common in marine, freshwater and even moist 5terrestrial ecosystems- most are heterotrophic but also some mixotrophic species- Mixotrophic species show unique primary endosymbiosis (how to get mitochondria and chloroplasts) (see fig 28.19)Archaeplastids- are the closest relatives of land plants- often included as
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