Protists
Useful Reading
Campbell, Biology 6th Ed - Chapter 28, pgs 545-574
Campbell, Biology 7th Ed - Chapter 28, pgs 549-572
Protists are a very large, diverse group of organisms, including the plant-like protists (algae), fungi-like protists, and the animal-like protists (protozoans). They are all eukaryotic, and most are unicellular. Traditional taxonomy of protists (Kingdom Protista) did not accurately represent evolutionary relationships, so the classification of this group is unsettled. Modern taxonomy has rearranged the group formerly known as Kingdom Protista, separating the different types of organisms into their own candidate Kingdoms.
Protists vary in how they obtain energy (autotrophic or heterotrophic) and in their locomotion.
Locomotion
Movement is achieved by several different methods in the protists.
Cilia - Microscopic hair like projections extending from the surface of a cell or unicellular organism. Capable of rhythmical motion, they act in unison to bring about the movement of the cell or of the surrounding medium
Paramecium
Flagella - A long, threadlike appendage, especially a whip like extension of certain cells or unicellular organisms, found singly or in pairs.
Euglena
Pseudopodia - A temporary projection of the cytoplasm of certain cells, such as phagocytes, or of certain unicellular organisms, especially amoebas.
Amoeba
Energy obtainment
Protists are classified by how they acquire energy. Often a single method is specific to a single protist. There are four grouping of how energy is obtained.
Photosynthetic autotroph
Chemosynthetic autotroph
Heterotroph by ingestion
Heterotroph by absorption
Photosynthetic autotrophs make their own food using energy from light to power complex chemical reactions to make glucose. Chemosynthetic autotrophs do the same thing using energy obtained from the breakdown of chemicals.
Heterotrophs require food as they cannot make their own. Heterotrophs by ingestion eat by consuming food; taking it into their bodies to be digested by enzymes. Nutrients are then released from within the body. Heterotrophs by absorption eat by secreting digestive enzymes outside of their bodies, then absorbing the nutrients into their bodies.
Diversity according to proposed Candidate Kingdoms
Candidate Kingdom Archaezoa
Lack mitochondria, made up of several hundred species, most
are parasitic
Trichonomads, Diplomonads and Microsporidians
-Order Trichomonadida
Parasitic
Example Trichomonas: note the anterior flagella
-Order Diplomonadida
Flagellates
Example Giardia
Candidate Kingdom Euglenozoa
All have anterior chamber from which 2 flagella emerge
Euglenophyta and Zoomastigophora
-Phylum Euglenophyta
(Photosynthetic Flagellates)
Photosynthetic
Flexible pellicle for wall
Motility by flagella
~ 800 species
Example Euglena : flagella, pigment spot (or stigma),
positive phototaxis
- Phylum Zoomastigophora
(Non-Photosynthetic Flagellates)
Non-photosynthetic
Motility by flagella
Thousands of species
Single Mitochondrion
Concentration of
extra-nuclear DNA
Commonly called
kinetoplastids
Variety of ecological associations: free-living, parasitic,
mutualistic
Example Trypanosoma
: human parasite that causes African sleeping sickness, transmitted by
tsetse flies
Example Trichonympha : symbiont in termite gut, digests cellulose
Candidate Kingdom Alveolata
All members of this group have small indentations in
their cell membranes, called alveoli, beneath the material covering the outer
surface
Pyrrophyta, Ciliphora and Apicomplexa
-Phylum Pyrrhophyta /
Dinoflagellata
Most forms with
cellulose "armored" plates (theca)
Most marine (brown algae); large component of phytoplankton
Two flagella in grooves
Photosynthetic
Reproduction mostly fission
Some symbionts
~ 1,000 species
Example Ceratium
Dinoflagellates :
Source of red tides, can produce toxins, cause paralytic shellfish poisoning,
cause many tropical fish poisonings
- Phylum Ciliophora
(Ciliates)
Locomotion by cilia
Multilayered pellicle
Heterotrophic, many feeding modes
Two types of nuclei: macronucleus and micronuclei
~ 8,000 species
Reproduce sexually
Examples Paramecium
(see above in locomotion section), Stentor (left) and Vorticella
(right)
Candidate Kingdom Stramenopila
All have unusual flagella with fine hair like projections
Bacillariophyta, Oomycota, Phaeophyta and Chrysophyta
- Phylum Bacillariophyta (Diatoms)
Photosynthetic
Freshwater and marine; large component of phytoplankton
Cell walls are two valves with silica; overlap at the girdle
Abundant fossils (diatomaceous earth)
~ 11,500
species
Reproduction mostly by fission
-Phylum Oomycota (water molds
and parasitic fungi-like protists)
Vegetative hyphae
Sexual reproductive
structures, oogonium and antheridium
Zygote is called an
oospore
Asexual reproduction by biflagellated zoospores
Cellulose cell walls
Heterotrophic, decomposers and parasites
~ 500 species
Example Saprolegnia
-Phylum Phaeophyta (Brown Algae
or Kelps)
Marine tidal zone to 75 feet deep in temperate waters
Sizes to 10O feet
Color: brown to olive brown
Pigments: Chlorophyll a and fucoxanthin
All multicellular
Many commercial uses
Body Form has a Holdfast, Stipe, Lamina (Blade), and Air bladders
Well defined alternation
of diploid and haploid generations
Sporophyte (diploid
stage) dominant
Reproductive cells flagellated
Vegetative Reproduction by Fragmentation, Propagules, or Zoospores
Examples Laminaria (left) and Nereocystis (right)
Example Sargassum
-Phylum Chrysophyta (Chrysophytes / Golden algae)
Candidate Kingdom Rhodophyta
Commonly called coralline algae because of calcium
carbonate in cellulosic cell walls
None of the life cycle stages have flagellated cells
Rhodophyta
-Phylum Rhodophyta (Red Algae)
97% marine
~ 4,000 species
Size to 3 feet, depths to 300 feet
Colors: red, purple, black
Shapes: Unicells, Branching filaments, Sheetlike
No flagellated cells
Pigments: Phycobiliproteins (Phycocyanin, Phycoerythrin), Chlorophyll
a
Gametophyte forms gametes, gametes fuse to form Sporophyte
Sporophyte may make many types of sporangia and spores
Source of agar
Examples Porphyra (left) and Rotalgen (right)
Candidate Kingdom Mycetozoa (Slime
Molds)
Myxomycota and Acrasiomycota
-Phylum Myxomycota / Myxogastrida (Plasmodial
slime molds)
Naked protoplasm or multinucleate plasmodium stage
Nuclei are generally diploid
Heterotrophic (Phagotrophic)
Produce sporangia for sexual reproduction
-Phylum Acrasiomycota /
Dictyostelida (Cellular slime molds)
Alternate between
amoeboid cells, flagellated cells and plasmodium
Stage (called a slug)
which is multicellular not multinucleate
Nuclei are generally haploid
Produce asexual fruiting bodies
Candidate Kingdom Chlorophyta (We
will study with Non-flowering Plants)
All have bright green choloroplasts
Very close relationship with plants
-Phylum
Chlorophyta (Green Algae)
~ 7000 species
Mostly freshwater
Shapes: Unicellular, Colonial, Filaments, Sheet-like (thallus)
Color: Mostly "grass-green"
Cell walls have cellulose and pectin
Food reserve is starch (stored in pyrenoids)
Pigments: chlorophyll a and b, carotenoids -- like higher plants
Reproduction: Vegetative - Fission, Fragmentation
Reproduction: Sexual - Isogamy, Anisogamy, Oogamy, Conjugation
Sacrodina (Undetermined protist
groups)
Amoebas, Radiolarians and forams
All move by pseudopod formation
-Phylum Rhizopoda
Heterotropic
protozoans
Lack permanent locomotive organelles like cilia or flagellae
Move and catch prey with transient cellular extensions, pseudopods
Example Amoeba
(see above in Locomotion)
-Phylum Actinopoda (Radiolarians [left] and Heliozoans [right])
- Phylum Foraminifera (Forams)
Locomotion by pseudopodia
Heterotrophic; feeding by phagocytosis
Many secrete shells
Examples Radiolaria (Silica) and Foraminifera (CaCO3)
Review Questions
-What protists are the major components of phytoplankton?
-What causes red tides?
-What are commercial uses of algae?
-What cell components are used by protists for locomotion?
-Why do some brown algae have air bladders?
-Which photosynthetic pigments are used by brown algae (Phaeophyta), red algae (Rhodophyta), and diatoms (Bacillariophyta)?
-Which protists are heterotrophic?
-What is positive phototaxis and why does Euglena demonstrate it?