Bio 103
Winter Quarter
Lake Tahoe Community College
Instructor: Sue Kloss
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Protists - Ch. 28
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Intro - Protists have long been identified as nucleated unicellular organisms and their direct descendants. However, bio
prospecting has identified many more species, and the Kingdom Protista has been abandoned as more molecular
evidence has come to light. Some organisms that were formerly classified as protists have been found to be more close
related to organisms in other kingdoms. The term protist is still used by many biology books and biologists to refer to euks
that are not plants, animals or fungi.
I. Protists are an extremely diverse assortment of eukaryotes – they have a nucleus and membranous organelles.
A. Most are unicellular, but as cells, are amazingly complex and diverse, even in size. (fig. 28.1)
1. They have to do in one cell what other organisms have specialized cells and tissues to accomplish.
a. they carry out all metabolic processes with subcellular organelles, not multicellular organs
2. Most nutritionally diverse of all euks
a. heterotrophs- absorb or ingest organic molecules or particles
b. photoautotrophs - contain chloroplasts
c. mixotrophs - combine photosynthesis and heterotrophic nutrition
3. All of these have arisen independently in many protist lineages
4. Ecologically, we can divide protists up into 3 groups- Algae are photosynthetic (Plant like),
Protozoans are ingestive (animal like), and fungus like protists, which absorb their nutrition
5. Most protists are aquatic, and live anywhere there is water including leaf litter and puddles
a. many live in benthic environments
1. attach to rocks
2. creep thru sand and silt
b. also important constituents of plankton, form basis of marine food webs
6. Protists are diverse in reproduction- some reproduce asexually, some sexually
B. Endosymbiosis in eukaryotic evolution
1. Endosymbiosis- process where one organisms engulfs another without digesting it, and the internal
cell becomes an endosymbiont and ultimately organelles in the host cell,
a. eg. ancestral euks engulfed proteobacteria with mitochondria
b. cyanobacteria engulfed by heterotrophic euk -become plastids, including chloroplasts
2. secondary endosymbiosis - algae were engulfed by chlorarachniophytes and euglenids (Fig. 28.2)
C. One current hypothesis breaks eukaryotic diversity into 5 “supergroups”
1. Excavata – “excavated” groove along the body
2. Chromalveolata – membranous sac under plasma membrane; includes brown algae such as kelp
3. Rhizaria – contains most species of amoebas that have thread-like pseudopodia
4. Archaeplastida – red and green algae, along with land plants
5. Unikonta – amoebas with lobe or tube-shaped pseudopodia
II. Excavata include protists with modified mtiochondria and protists with unique flagella. Many also have a groove on one
side of the body.
A. Protists in this group include diplomonads and parabasalids, which lack plastids, mitochondria have no DNA,
etc, or enzymes for CAC; most are anaerobes
B. Diplomonads
1. have 2 equal sized nuclei and multiple flagella
a. microtubules in cytoplasm covered by plasma membrane
b. proks have protein flagellin attached to cell surface
2. lack functional electron transport chains – so don’t use O2
3. Giardia is a diplomonad - causes diarrhea and cramps, cysts endure in water - boiling will kill them
C. Parabasalids
1. include protists called trichomonads, including Trichomonas vaginalis (fig. 28.4)
a. moves along mucus membrane w/ flagella and undulations of membrane
b. if normal acidity of vagina is disrupted, it can outcompete normal inhabitants and infect lining
c. can be sexually transmitted - feed on epithelial cells of vagina or male’s urethra (may be
asymptomatic)
D. Eugelnozoans clade contains hetero and autotrops, as well as parasites. Most have flagella with a unique
internal structure - crystalline rods with unknown function (fig. 28.5)
1. Kinetoplastids have a single large mitochondrion that contains organized mass of DNA called a
kinetoplast
a. some are freeliving consumers of proks
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b. others are parasites of plants, animals, protists
1. Trypanosoma causes sleeping sickness spread by Tsetse fly (fig. 28.6)
2. Trypansomes also cause Chagas’ disease which causes heart failure
a. evade immune system detection by switching surface proteins ea. generation
b. host can’t develop immunity
c. .33 of genome is devoted to these proteins
2. Euglenids - have a pocket at one end from which 2 flagella emerge; many are mixotrophic (Fig 28.7)
a. paramylon- a glucose polymer that functions as storage molecule is found in euglenids
b. euglenids are autotrophic, but when sunlight is unavailable, become heterotrophs absorbing or
engulfing food
IV. Chromalveolates – large and very diverse clade – most controversial of those proposed here.
1. Alveolates - membrane bound sacs beneath the plasma membrane; function unknown, perhaps osmoregulation, or
stabilization of cell surface.
A. Dinoflagellates - abundant in marine and freshwater phytoplankton (fig 28.8 and 9)
1. many are photosynthetic , but about half of know speices are heterotrophic
2. some are colonial, most unicellular
3. characteristic shaped cellulose “armor”.
4. 2 flagella in grooves of this armor make them spin as they move thru water
a. red tide caused by dinoflagellates - toxins can kill invertebrates, fish and even humans
b. some are spectacularly bioluminescent
c. important food source in reef communities
B. Apicomplexans - all are parasites - apical complex has structure for penetrating host cells (fig. 28.10)
1. all have nonphotosynthetic plastid used for making fatty acids or other vital functions
2. most have intricate life cycles requiring 2 hosts for completion
a. malaria - human and mosquito (fig. 28.10) - Anopheles mosquito
b. continually changes surface proteins, like Trypanosomes
c. both mosquitoes and parasite have become resistant
d. 300 million humans are infected, 2 million die each year
C. Ciliates - use cilia to move and feed - contain micro and macronuclei
1. Paramecium is a common ciliate (Fig. 28.11 details many functions and structures)
2. Stramenopiles have “hairy” and smooth flagella
A. stramenopiles have flagella that has numerous, fine hairlike extensions; also have non-hairy flagellum (28.12)
B. Oomycetes (Water molds and their relatives, white rusts and downy mildews)
1. thought to be fungi bc of high ratio of filaments (convergent evolution), but now are classified as
protists – (fig. 28.17)
a. walls made of cellulose, not chitin (fungal material)
b. have flagella (almost no fungi have flagella)
c. diploid condition predominates (diminished in fungi)
2. acquire nutrients as decomposers or parasites (Fig. 28.14)
a. water molds grow as cottony masses on dead algae and animals
b. white rusts and downy mildews generally live on land as parasites of plants
c. Phytophthora 1. potato blight in Ireland in 1800s, still kills 15% of US potato crop
2. sudden oak death here in CA
B. Diatoms - unique glasslike wall of silica (Fig. 28.13)
1. fit like shoe box and lid
2. effective against crushing jaws of predators - same as legs of a table supporting an elephant
3. reproduce asexually by mitosis
a. each new daughter cell receives half parental cell wall and generates new half to fit it
b. sexual repro uncommon
4. considered a type of algae, very important food web components
5. some store food as oil
6. become part of ocean sediments, uplifted are diatomaceous earth - prized for filtering capacity
C. Golden Algae (Fig. 28.14)
1. chrysophytes - Gr. chrysos = golden - yellow and brown carotenoids
a. cells biflagellated on one end
b. many are freshwater and marine plankton
c. unicellular, or occasionally colonial
2. all are photosynthetic, some are mixotrophic
3. can form cysts if cell density is too high that persist for decades
D. Brown Algae - largest and most complex algae
1. phaeophytes - Gr. phaios = brown
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a. most are marine and multicellular
b. common along temperate coasts. where water is cool
c. brown due to carotenoids in plastids
2. along with red and green algae, make up many of what we call seaweeds
a. seaweeds have most complex multicellular structure of all algae, even having specialized
tissues and organs
b. evidence indicates that they evolved independently of plants
3. thallus = seaweed body that is plantlike -(Fig. 28.16)
a. lacks true leaves, stems and roots
1. rootlike holdfast
2. stemlike stipe
3. leaflike blades - most surface for Ps, may contain floats to keep blade near surface
4. kelps are brown algae, blades may be 60 m long
5. intertidal zone is a rough place- buffeting of waves, salt, air, varying water levels, sun
a. adaptations include:
1. cell walls have cellulose and gel-like polysaccharides to cushion thallus from waves
and drying
6. Human uses of seaweeds
a. food - kombu, sushi (Fig. 28.20)
b. gel forming substances used to thicken puddings, icecream etc.
7. Alternation of generations
a. alternate multicellular forms of haploid and diploid cells
VI. Rhizarians have threadlike pseudopodia - turns out amoebas are found in many distantly related taxa and many are
now in this group. This group has threadlike pseudopodia
A. Forams -named for porous shells, called tests
1. tests gen’ly multichambered, organic material hardened with calcium carbonate (calcareous)
2. pseudopods extend thru pores function in swimming, test formation, feeding
a. many forams have symbiotic relationships w/ algae in tests and derive sugar from them
3. forams are both marine and freshwater
a. most live in sand or sediments or attach to rocks or algae, though some abundant in plankton
b. single celled, but may grow to diameter of several cm
4. excellent in fossil record along with calcareous remains of other organisms
a. components of marine sediments and uplifted land formations
b. excellent for correlating the ages of sedimentary rocks indifferent parts of the world
B. Radiolarians - mostly marine protists - tests fused into one delicate piece made of silica (fig. 28.18)
1. pseudopods called axopodia extend from central body,
a. reinforced by microtubules covered by cytoplasm
b. can phagocytize smaller organisms that attach to axopodia
2. when radiolarians die, tests settle into sediments as ooze hundreds of m thick in some places
VII. Archaeplastida - red Algae and Green algae are the closest relatives of land plants - more than a billion yrs ago, a
heterotrophic protist acquired a cyanobacteria symbiont - descendants evolved into red and green algae. 475 mya, green
algae gave rise to land plants
A. Red algae - pigment called phycoerythrin 1. masks green chlorophyll - in shallow water have less, so may appear green or black
a. the most abundant land algae in warm coastal waters
b. pigments allow them to absorb blue and green light which penetrate farther into the water
2. most are multicellular, largest are called seaweeds (Fig. 28.19)
a. thallus may be filamentous and lacy
3. alternation of generations is common
a. no flagellated stages, so depend on flow of water to bring gametes together
B. Green algae - structure is plantlike, and they have grass green chloroplasts, 2 grps - chlorophytes and
charophyceans.
1. Chlorophytes may be uni or multicellular; plankton or symbionts (some are lichens, for example)
a. found in high elevation glaciers and snowfields (Fig. 28.20) - watermelon snow
1. UV blocking compounds in cytoplasm
b. larger size and greater complexity due to: (Fig. 28.21)
1. colonialism (Volvox)
2. nuclear division w/ no cytokinesis to form larger organism
3. multi cellular forms with cell division and differentiation - seaweeds, such as Ulva
2. charophyceans will be discussed with plants
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VIII. Unikonts – includes protists as well as animals and fungi. Amoebozoans have lobe shaped pseudopodia - rather
than threadlike, as are the rhizarians
1. One major clade is the Amoebozoans
A. Gymnamoebas - unicellular, found in soil as well as marine and freshwater
1. heterotrophs that actively seek and consume bacteria, small protists or detritus (fig. 28.24)
B. Entamoebas - internal parasites infecting all classes of vertebrates as well as some invertebrates
1. Humans host 6 spp., but only one known to be pathogenic - causes amoebic dysentery,
a. 3rd leading cause of death from parasites
C. Slime Molds - once thought to be fungi because of fruiting bodies that aid in spore dispersal (convergence)
1. plasmodial slime molds - many brightly pigmented (Fig. 28.24), yellow or orange
a. form a plasmodium many cm in size (different from Plasmodium which causes malaria)
1. one huge cell with many nuclei, undivided by membranes - mitosis w/ no cytokinesis
2. plasmodium extends thru moist soil or rotting plant matter, extending pseudopodia and
engulfing food particles
3. if habitat dries up, plasmodium dries up and produces fruiting bodies for reproduction
4. predominant condition is diploid
2. Cellular slime molds
a. feeding stage are solitary cells that function individually
b. when food depleted, aggregate into mass that functions as a unit (Fig. 28.25)
1. resembles plasmodium, but cells retain membranes
2. no flagellated stages and mostly haploid, unlike plasmodial slime molds
2. Another major clade includes Opisthokonts – includes animals, fungi and several groups of protists.
IX. Ecologically speaking, protists are critically important
Ch. 28 Objectives
1. Explain why the kingdom Protista is no longer considered a legitimate taxonomic group.
2. Describe the different nutritional strategies of protists.
3. Describe the three ecological categories of protists. Explain why the terms protozoa and algae are not useful as
taxonomic categories.
4. Describe the evidence that supports the theory that mitochondria and plastids evolved by serial endosymbiosis. Explain
which living organisms are likely relatives of the prokaryotes that gave rise to mitochondria and plastids.
5. Explain the role of secondary endosymbiosis in the evolution of photosynthetic protists
6. Explain how trypanosomes avoid detection by the human immune system.
7. Explain why Plasmodium continues to pose a great risk to human health despite modern medical advances.
8. List three differences between oomycetes and fungi.
9. Describe the ecology, and impact on humans of the following stramenopiles:
a. downy mildew
b. diatoms
c. kelp
10. Describe how amoeboid protists move and feed.
11. Explain why foraminiferans and gymnamoebas are not considered to be closely related, although both are amoebas.
12. Compare the ecology of plasmodial and cellular slime molds.
13. Describe three mechanisms by which large size and complexity have evolved in chlorophytes.
14. Make a table that includes the 5 protistan supergroups proposed for Eukarya. Include several important members of
each group along with key ID characteristics, and why they are important.
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