What is a Protist?

How are Protists related to other eukaryotes?

Does everyone agree how to classify protists?

• No, at present, biologists do not agree how to classify protists • The amount of diversity among the protists, is much greater than within or between the other three eukaryotic kingdoms

The Protist Dilemma

• Protists are grouped together solely because they are not fungi, plants or animals • Furthermore, many protists are more closely related to members of other eukaryotic kingdoms than they are to other protists.

Current Protist classification

• It has been proposed that the protista kingdom be divided into six groups or clades • Today, while we still use the term Protist, this is not a single kingdom, but a collection of organisms in six clades

What is a Protist?

• • A protist is a eukaryote (has a nucleus) A protist is any eukaryote that is not a plant, animal or fungus

Evolution of Protista Endosymbiont Hypothesis

Are all protists unicellular?

• No, although most are unicellular, some protists are colonial, and some like the giant kelp are multicellular.

Unicellular Colonial Multicellular

How do Protists Move?

• • • Some move with flagella Long whip-like projections One to two per cell Examples – – Trypanosoma Euglena

Trypanosoma

 Two flagella  No cell wall  Chloroplasts

Euglena

How do Protists move?

 Some move with cilia  Cilia can be used for feeding and movement  Cilia are short and used like oars on a boat  Example  Paramecium

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Ciliates - Paramecium

Lysosomes Trichocysts Oral groove Gullet Anal pore Contractile vacuole Micronucleus Macronucleus Food vacuoles Cilia

Some do not move

 Those that do not move produce spores and live as parasites  Plasmodium causes malaria 

Cryptosporidium

spreads through contaminated drinking water and caused intestinal disease

Excavates:

feeding groove, flagella • • Diplomonads – Giardia is an intestinal parasite that causes cramping and diarrhea Discicristates – Euglena is free living and can use its chloroplast for photosynthesis or can live as a heterotroph – Trypansoma causes African sleeping sickness; carried by tsetse flies

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Euglena

Flagella Gullet Eyespot Chloroplast Carbohydrate storage bodies Pellicle Nucleus Contractile vacuole

Chromalveolates:

very diverse group; most are photosynthetic • • • • • • Phaeophytes = multicellular brown algae Chrysophytes = unicellular golden algae Diatoms = unicellular algae with intricate silicon dioxide (silica) shells Ciliates = paramecium are not photosynthetic Dinoflagellates = half are photosynthetic, half are heterotrophs; some are luminescent Apicomplexans = parasitic Plasmodium

Brown algae

• • • • • Phaeophytes Photosynthetic Chlorophylls a and c Brown accessory pigment fucoxanthin Multicellular Giant kelp, Fucus

Photosynthetic protists

• Chrysophytes  “Golden plants”  Gold-colored chloroplasts  Cell walls contain pectin instead of cellulose  Store food as oil rather than starch  Can form thread like colonies

Photosynthetic protists

Diatoms  Glass like cell walls  Cell walls contain silicon (Si)  Cell walls like petri dish

Photosynthetic protists Dinoflagellates  Luminescent  “Fire plants”  Half photosynthetic  Half heterotrophs  Two flagella

• •

Plasmodium

Mosquito borne parasites like the species that causes malaria

Apicomplexan

Cercozoa, Foraminiferan, Radiolarian

• • Have pseudopods Many produce protective shells Heliozoan Foraminiferans

Rhodophytes

• • • • • • Red Algae Chlorophyll a Red accessory pigment – phycobilin Absorbs blue light Grows very deep Multicellular Nori

Ecology of photosynthetic protists

• • Base of the food chain Half of the photosynthesis on earth is carried out by phytoplankton

Ecology of photosynthetic protists

• Algal blooms  Caused by too much pollution or nutrients  Deplete water of oxygen  Kill fish and invertebrates  Dinoflagellates cause “red tides”  Red tides produce toxins which can be taken in by shellfish. Eating these shellfish can cause illness, paralysis and death

Green algae

• • • • • • • Phylum Chlorophyta Same chlorophyll and cell wall composition as green plants Chlorophyll a and b Store food as starch Found in fresh and salt water and on land Unicellular, colonial and multicellular Now classified with plants

Unicellular green algae •

Chlamydomonas

 Lives in ponds, ditches and wet soil  Egg shaped  Two flagella  Large, cup-shaped chloroplast

Colonial green algae • •

Spirogyra

 Filamentous  Forms threadlike colonies  Spiral chloroplasts

Volvox

 Hollow spheres  500 – 50,000 identical cells  Some cell specialization

Human uses of algae

• Oxygen • Food (nori; thickening agent (carrageenan) in ice cream, egg nog, chocolate, salad dressing) • Industry (plastics, waxes, paints, lubricants) • Science labs (agar)

• • • • • Alternation of generation – alternating between diploid and haploid organisms Diploid – having two copies of each chromosome Haploid – having one copy of each chromosome Gametophyte – haploid gamete producing organism Sporophyte – diploid spore producing organism

Heterotrophic protists

• Amoebozoa = Amoebas use pseudopods for movement and feeding • Ciliates = Paramecia use cilia to move food to gullet; food vacuoles and lysosomes digest the food; waste is released through the anal pore • Slime Molds and Water Molds absorb food through their cell walls from dead or decaying matter; decomposers

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Section 20-2 An Amoeba

Contractile vacuole Nucleus Food vacuole Pseudopods

Slime molds

Slime molds

• • • •

Water molds

Cells are multinucleate Cell walls of cellulose White fuzz on dead fish in water Plant parasites on land

Cause potato blight responsible for potato famine

Reproduction in water molds • • • • Can produce sexually and asexually Motile (swimming) spores Antheridium produces sperm Oogonium produces eggs

Mutualistic relationships

• Zooxanthellae – live inside coral and provide food through photosynthesis •

Trychonympha –

live in the gut of termites and digest cellulose