Protists
Protists, formerly of the group Protista, are single-celled (mostly)
eukaryotes exhibiting more diversity than any other single group of
organisms. The origins of these specialized organisms is in the
endosymbionts that helped the single celled organisms evolve. (ex:
cyanobacteria and red/green algae) Secondary endosymbiosis further
specializes the the organisms. (ex: Green algae and euglenids)
• Nutritional diversity
• Autotrophic (plant-like, photosynthetic) -algae
• Heterotrophic (animal-like, ingestive) -protozoans
• Mixotrophic (autotrophic & heterotrophic, fungus-like, absorptive)
• Habitats
• Most are aquatic
• Reproductive lifestyles
• Asexual
• Sexual
• Syngamy
• Main Clades (groups)
Diplomonads
• 2 equal sized nuclei
• multiple flagella
• Giardia intestinalis- pathogen causing severe diarrhea
Parabasalids
• Include the Trichomonads
• Trichomonas vaginalis - pathogenic organism causing changes in pH
and infection in the reproductive tract of females
• can live in the urethras of males and be transmitted sexually
• may have become pathogenic with horizontal transfer of genes through
endosymbiosis
Euglenozoans
• Characterized by specialized flagella containing crystalline rods
(unknown function) and disk-shaped mitochondrial cristae
• Kinetoplastids
• single large mitochondria containing a stack of DNA called a kinetoplast
• consumes prokaryotes in almost any aquatic environment
• Trypanosoma - African sleeping sickness
• able to change surface proteins to evade immune systems
Euglinoids
• 1 or 2 flagella that extend from a pocket
• large glucose polymer (paramylon) that is used for storage
• are mixotrophic engulfing via endocystosis when light is unavailable
for photosynthesis
Alveolates
• Contain small membrane bound sacs (alveoli) within their plasma
membranes.
• Dinoflagellates
•
•
•
•
•
Live in fresh or salt water
Major component of phytoplankton
Primarily unicellular but some are colonial
2flagella located in perpendicular groves (causes a spinning motion)
Causes red tide - toxic to fish and invertebrates.
• Toxic to humans consuming mollusks caught during a red tide.
• Some exhibit bioluminescence - half moon bay
• Mutualistic symbiont of coral reefs providing photosynthetic products to the coral
reefs
Apicomplexans
• Parasites of animals
• Sporozoite stage lives in the animal
• Apex has a complex of organelles used in the penetration of host tissues
• Many have sexual and asexual stages and require a vector for
insertion into the host
• Anopheles(mosquito) transmits the Plasmodium parasite to humans causing
malaria
• Malaria has been hard to treat as the sporozoite lives inside the human cell
and is able to change its surface proteins to evade the host's defenses
Ciliates
• Use cilia for locomotion and to locate prey
• Can surround body or be clumped
• Paramecium
• Genes are packaged into smaller units - located in the macronucleus which
controls the functions of the protist
• Can have many macro & micro nuclei
• Reproduce asexually via binary fission
• Genetic variation via conjugation
• May use the process to remove transposons from their genome
Oomycetes
• molds and mildews
• similar to fungi
•
•
•
•
walls contain cellulose (not chitin)
multi-nucleate hyphae (filaments)
diploid stage predominates life cycle (haploid predominates fungi)
have flagella (which most fungi lack)
• cause of blights and rusts that affect many crops
Diatomes
• unicellular algae
• 2 parts resembling the parts of a shoe box
• Cell wall made of hydrated cilica
• Makes them extremely strong
• Most reproduce asexually
• Major component of phytoplankton
• Store food as either starch (laminarin) or oils
• Used as filter medium (diatomacious earth)
Golden Algae
• Chrysophytes- named for color
• Yellow and brown carotenoids
• majority are photosynthetic with some being mixotrophic
• Component of phytoplankton
• Most are unicellular with some being colonial
• May form cysts for survival in water supply is depleted (like
endospores)
• phaeophytes - dusky brown
• Largest of the algae - may grow to 60m long
• All multicellular
• Mostly marine - seaweeds
•
•
•
•
•
Brown Algae
parts
thallus- body (no true roots)
holdfast- root-like appendage that attaches to rocks
stipe- supports the blades
blades- leaf-like surface
• maybe equipped with floats to keep near the surface
• exhibitsalternation of generations much like plants
Cercozoans & Radiolarians - threadlike
pseudopodia
• Foraminiferans
•
•
•
•
•
porous hard shells made of calcium carbonate
thin pseudopodia extend through the pores for locomotion (swimming)
obtain nutrition through photosynthesis via symbiotic algae
single-celled
component of plankton
Radiolarians
• shells made of silica
• pseudopodia radiate from the center and are reinforced with
microtubules
• called axopodia
• used for phagocytosis
Amoebozoans - lobed shaped pseudopodia
• Gymnamoebas
• heterotrophic inhabitants of all aquatic environments
• consume prey via phagocytosis
• some are decomposers
• Entamoebas
• parasites of all classes of vertebrates
• E. histolytica - causes dysentery (watery diarrhea) in humans
Slime Molds
• Plasmodial slime molds
• cells divide by mitosis without cytokinesis
• results in a mass of multinucleated cytoplasm that is not separated by a membrane
• can grow to a diameter of many centimeters
• usually yellow or red in color
• distributes oxygen and nutrients via cytoplasmic streaming within the super
cell
• heterotrophic vis phagocytosis
• develops fruiting bodies when water of food dries up (like a mushroom)
• produces flagellated spores used in sexual reproduction (syngamy)
Cellular slime mold
• single celled when food is good
• aggregate into a super cell when food is scarce
• cells are still separated by a membrane
• Fruiting bodies are haploid and used in asexual reproduction
• no flagellated stage
Red & Green Algae
• closest relatives to plants. Share a common symbiont cyanobacteria.
• Red Algae
• The amount of red pigment (phycoerythrin) is directly related to the depth
that the organism grows
• at great depths the organism appears dark red (almost black) as the red pigment masks
the green chlorophyll
• absorbs primarily blue light at this depth
• at shallow depths the organism appears greenish as chlorophyll is more abundant
• multicellular
• largest of the species are classified as seaweeds
• live primarily in warm marine environments
Green Algae
• named for their grass green chlorophyll
• most closely related to plants as their structure and function are closely
related
• most live in fresh water
• unicellular or multicellular
• flagellated or nonflagellated
• some are plankton
• some are symbionts living in other organisms
• some are colonial with the largest multicellular varieties being classified as
seaweeds