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ProtistsClassifying the
Exceptions
What are Protists?• Those organisms that cannot be classified as Monerans, fungi, plants or animals
• Created as a group because of classification problems
• Some share characteristics of more than one other kingdom
• Example: – Euglena has chloroplasts & is an autotroph like plants,
– but has no cell wall and can swim using a flagella, so also like an animal
Characteristics of Protists
• Almost all are unicellular – A few are colonies of identical cells
• Are distinguished from unicellular Monerans because they are eukaryotes – Have a nuclear membrane– Have mitochondria and other organelles
• A diverse group with diverse characteristics– some are plant-like, autotrophs algae– some are animal-like, heterotrophs protozoans
– some are fungus-like, decomposers slime molds
Plant-like Protists
• 10,000 species of plant-like protists
• Divided into 3 phyla– Phylum Euglenophyta– Phylum Pyrrophyta
•dinoflagelates, plankton– Phylum Chrysophyta
•diatoms
Phylum Euglenophyta• Most have chloroplasts - are autotrophs• Have a large nucleus and nucleolus• Have large chloroplasts
– these disappear if the organism is placed in the dark
• No cell wall– on the outer surface of the cell are spiral strips of protein which form a pellicle - give cell shape
• Can move by changing shape• Have 2 flagella: one long, one short• Have an eye spot
– an area of red pigment that is sensitive to light
• A gullet opens into reservoir• Reproduce asexually
Euglenoids
Freshwater Protists• Euglenoids live in fresh water ponds and lakes– The single-celled organism is in a hypotonic solution
– Water diffuses in by osmosis
• No rigid cell wall• These organisms have to have an other means to prevent the cell membrane from bursting
• Contractile vacuole controls water balance– Pumps excess water back out of the cell
The Contractile Vacuole
Phylum Pyrrophyta• Most common are dinoflagellates • Unicellular algae with 2 flagella • Most are marine
– Many plankton (small organisms near the surface of the ocean) are dinoflagelates
• Mitosis is somewhat like prokaryotes– some scientists believe are intermediate form between prokaryotes and eukaryotes
Dinoflagellate Characteristics
• Most have chloroplasts with chlorophyll– red & yellow pigments mask the green
• Most have a cellulose cell wall• Segments fit together like armor• Most have 2 flagella
– One extends back from the middle of the cell - propels the organism
– 2nd wraps around middle in a groove - vibrates causing cell to spin
• Chromosomes are visible in dinoflagellates
• Some produce toxins - red tide!• Many produce light - bioluminescence
A Dinoflagellate
Phylum Chrysophyta• Most are diatoms - live in fresh and salt water
• Most are photosynthetic– Most are gold or brown from pigments other than chlorophyl
• Most don't have flagella• Have cell walls with 2 overlapping halves– composed of pectin - a gelatinous material; also contains silica
• Reproduce a sexually
Diatoms
Multi-cellular Algae• Many algae have multi-cellular bodies
– Body of a multi-cellular algae = thallus• Once classified as plants because they have chlorophyll and perform photosynthesis
• Now usually classified as protists because they have reproductive structures different from plants
• Three phyla:– Chlorophyta = green algae– Rhodophyra = red algae– Phaeophyta = brown algae
Red Algae
Volvox – A Colonial Green Algae
Spirogyra Conjugation
Kelp – A Brown Algae
Protozoans• Animal-like protists
– Are heterotrophs– Can move
• Classified by their means of movement
• Four diverse groups:– Sarcodinians– Zooflagellates– Ciliaphorans– Sporozoans
Sarcodinians• Protozoans that move by extending lobes of cytoplasm– Pseudopods = false feet
• Example: amoeba• Some have hard shells of calcium carbonate or silica– Extend pseudopods through holes in their shells
• Examples: foraminferans & radiolarians
The Amoeba
Radiolarian
Heliozoan
Zooflagellates• Protozoans that move by means of a flagella
• Many are free-living freshwater or marine organisms
• Many live in symbiotic relationships with other organisms– Example: Trichonympha live in the guts of termites and digest cellulose
• Some are parasites that cause disease– Example: Trypanosoma causes African sleeping sickness
Trypanosomes
Trichomona
Ciliaphorans
• Protozoans covered with hair like projections, cilia, used to move
• The largest and most diverse group
• Examples:– Paramecium– Stentor
The Paramecium
Sporozoans
• Have no structures for movement• Live as parasites on other animals
– Spore-forming parasitic protozoans
• Have complex life cycles that include both sexual and asexual phases
• Some cause human diseases– Example: plasmodium causes malarial carried by mosquitos
Fungus-like Protists
• Live in damp, watery places• Decomposers• Extract nutrients from dead organisms
• Three groups:– Plasmodial slime molds– Cellular slime molds– Water molds
Plasmodial Slime Molds
• Have different forms at different stages in their life cycle
• Plasmodium = feeding stage• Forms a fruiting body that produces spores
• Spores unite to form amoeboid zygote the second stage
• Mitosis of the zygote regenerates the plasmodium
Slime Mold
Cellular Slime Molds• Live in fresh water, damp soil, or decomposing plant material
• Also alternate between an amoeboid form and a spore-producing fruiting body
• Amoeboid stage is the feeding stage– Reverse of plasmodial slime molds
• Amoeboid stage can produce a pseudoplasmodium– “Pseudo” because the individual cells are still independent
• Pseudoplasmodium produces fruiting bodies
• Fruiting bodies produce spores
Water Molds• Used to be classified as fungi
– Fungi have cell walls that contain chitin
– Water molds have cell wall of cellulose– Water molds produce spores with flagella
– Fungi produce spores without flagella
• Are decomposers or parasites• Includes water molds, white rusts, downy mildews– Potato blight
Powdery Mildew