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