• Even a low-power microscope can reveal a great variety of organisms in a drop of pond water
• These amazing organisms belong to the diverse kingdoms of mostly singlecelled eukaryotes informally known as protists
• Advances in eukaryotic systematics have caused the classification of protists to change significantly

• now part of the Domain Eukaryota
– eukaryotes = true nucleus
– evolution of a nucleus for the genetic information
– evolution of membrane-bound organelles
• diverse group of single and colonial forms informally known as The Protists
• but Kingdom Protista really doesn’t exist anymore – too polyphyletic
• probably arose from more than one prokaryotic group
• 7 to 45 phyla recognized depending on zoologist

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• mixotrophs = combine photosynthesis and heterotrophic nutrition
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–
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• amoeba
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• old classification scheme – 5 kingdoms
• new classification scheme – 3 domains
• Phylogenetic classification of eukaryotes now produces five
Clades:
• 1. Excavata (Kingdom)
– trypanosomes, euglena
• 2. Chromalveolata (Kingdom)
– dinoflagellates, diatoms, ciliates, brown algae
• 3. Rhizaria (Kingdom)
• 4. Archaeplastida (unranked kingdom)
– red algae, green algae and land plants
• 5. Unikonta (unranked kingdom)
– slime molds, amoebas, fungi and animals

Clade: Excavata
Eukaryotic Phylogenetic Tree
Chromalveolata Rhizaria Unikonta Archaeplastida
Alveolata Stramenopila Amoebozoa (Opisthokonta) (Viridiplantae)
Ancestral eukaryote

– considered photosynthetic protists similar to algae
– like algae – the photosynthetic protists have chlorophylls found in chloroplasts
– BUT some can be parasitic to humans

– parasites of animals, plants and other protists
• Trypanosoma gambienese – sleeping sickness (neurological disease) &
Chagas’ disease (congestive heart failure) in humans

Life cycle
-cycles between the tse tse fly and the human
-different forms of the trypanosome depending on what host (fly vs. human) and where it is in the host
1.
fly injects the trypanosome
2.
multiplication in the human host – e.g. in the blood
3.
bit by fly and transfer back to fly
4.
multiplication in the fly’s gut and then in the salivary gland

– unicellular protist
– most are autotrophic & photosynthetic
– main characteristic two flagella that emerge from a “ pocket ” structure – long (locomotion) and short
– contain a large, contractile vacuole that gets rid of excess water that constantly flows into the protist
– eyespot (stigma) - near the flagella
• filters light
– light detector (photoreceptor) – detects the filtered light and results in movement toward the light direction
– Chloroplasts for photosynthesis – containing chlorophylls https://www.youtube.com/watch?v=f
I7nEWUjk3A

•
•
– “dinos” = whirling
– surrounded by a cell wall encrusted with silica - act as “ armor ”
– most are photosynthetic
– two flagellae – located in perpendicular grooves
• one flagella propels the dinoflagellate forward and causes it to spin
• the other flagella acts as the rudder
LE 28-10
Flagella

– capable of proliferating explosively – “ blooms ”
• “ red tide ” (carotenoid pigments found in the plastids)
• dinoflagellates produce a toxin that kills off invertebrates
– some can be bioluminescent – ATP driven reaction that creates a glow at night
• scares off predators

• use of cilia to move and feed
– cilia may completely cover the protist or may cluster in a few rows or tufts
• distinguished by the presence of two types of nuclei: macronucleus (large) and micronucleus (small)
– may have one or more of each type
– macronucleus – controls the everyday function of the cell
– micronucleus – exchanged during reproduction
Paramecium , like other freshwater protists, constantly takes in water by osmosis from the hypotonic environment. Bladderlike contractile vacuoles accumulate excess water from radial canals and periodically expel it through the plasma membrane.
50 µm
FEEDING, WASTE REMOVAL, AND WATER BALANCE
Thousands of cilia cover the surface of Paramecium .
Contractile vacuole
Micronucleus
Macronucleus
Paramecium feeds mainly on bacteria.
Rows of cilia along a funnel-shaped oral groove move food into the cell mouth, where the food is engulfed into food vacuoles by phagocytosis.
Oral groove
Cell mouth
Food vacuoles combine with lysosomes. As the food is digested, the vacuoles follow a looping path through the cell.
The undigested contents of food vacuoles are released when the vacuoles fuse with a specialized region of the plasma membrane that functions as an anal pore.

• freshwater protist – constantly taking on water
• they contain contractile vacuoles to get rid o the excess water https://www.youtube.com/watch?v=9Ynm5ZO
W59Q

• 100,000 species of unicellular algae
• surrounded by unique glass-like wall made of silica embedded in an organic matrix
• most are photosynthetic
• major component of plankton in fresh and marine environments – source of food
– upon death –sink to the bottom = diatomaceous earth
– active ingredient in detergents, fine abrasive polishes, paint removers, decoloring oils, filtering agents, components of insulation and soundproofing products, reflective paint additive

• brown algae – most complex of the algae
– all are multicellular and all are marine
– have the most complex multicellular anatomy of all algae
– some have specialized tissues like animals and plants
– include the seaweeds
– giant seaweeds in intertidal zones – kelps

• brown algae
– composed of a thallus = algal body that is plant-like
– thallus has a rootlike hold-fast which anchors the seaweed and a stem-like stipe that supports leaflike blades
– BUT there are no true roots, stems and leaves!
– blades – surface for photosynthesis
– blades can come equipped with floats to keep them near the surface
LE 28-18
Brown algae Thallus

• more than a billion years ago – heterotrophic protist ingested a photosynthetic bacteria
• these bacteria evolved into plastids for photosynthesis
• protist became the red and green algae
• 475 million years ago – green algae ancestors evolved into land plants
• red algae, green algae and land plants are now placed into the same clade based on molecular data – Archaeplastida
Plastid
Red algae Bacterium
Heterotrophic eukaryote
Plastid
Green algae

•
– named for the green chloroplasts
– chloroplasts contain chlorophyll pigments that are very similar to plants in structure and function
– 7000 species of green algae
• mostly freshwater
• chlorophylls pigments for photosynthesis
• sugar storage form = starch
• cell walls made of cellulose just like plants
• most are unicellular
• some are also multicellular - colonial, filamentous
(pond scum) and sheet-like forms

• e.g. Chlamydomonas – example of a unicellular algae
– two flagellae of equal length at the anterior end
– a pyrenoid for carbohydrate synthesis
– eyespot or stigma for movement towards light
– two small contractile vacuoles for getting rid of excess water

• not really multicellular
• colony of unicellular algae
– e.g. Volvox
• colony or 500 to 60,000 cells that resemble Chlamydomonas
• individual cells have eyespots – will orient toward the light
• cells at the equator are reproductive - called gonads  gametes for fertilization  zygote
• zygote undergoes mitosis to form a small daughter colony
• the daughter colony remains in the parental colony until it bursts free https://www.youtube.com/watch?v=9pjW1cMfTz8 https://www.youtube.com/watch?v=d8xs8F9gln0 https://www.youtube.com/watch?v=cmSs157KvTg
Volvox, a colonial freshwater chlorophyte. The colony is a hollow ball whose wall is composed of hundreds or thousands of biflagellated cells embedded in a gelatinous matrix. The cells are usually connected by strands of cytoplasm; if isolated, these cells cannot reproduce. The large colonies seen here will eventually release the small “ daughter ” colonies within them.

• recently proposed clade
• supergroup of eukaryotes that includes animals, fungi and some protists
• means “one flagella”
• two major clades:
• A. Amoebozoans: the amoebas & slime molds
• B. Opisthokonts: fungi and animals

• 2. Entamoebas
– parasitic amoebae
– infect all classes of vertebrates and some invertebrates
– humans are host to at least 6 species
– Entamoeba histolytica – amoebic dysentery
• third leading cause of death in the world due to parasites – 100,000 deaths each year
Amoeba movement: https://www.youtube.com/watch?v=o-PjvIRrbbw https://www.youtube.com/watch?v=FcCvhYmjaXE
Amoeba proteus