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Protists. Survey of Chapter 25. What is a Protist ?. Eukaryotic organisms that do not fit into any other category are usually called protists Most protists are microscopic, but some are multicellular (like algae)
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Protists Survey of Chapter 25
What is a Protist? • Eukaryotic organisms that do not fit into any other category are usually called protists • Most protists are microscopic, but some are multicellular (like algae) • We determine that an organism is a protist using EXCLUSION: it cannot be classified as a fungus, plant or animal • Protists are a very diverse group and it’s thought that they were the first eukaryotes
Classification • Protists are classified by what they resemble • Animal-like protists: • heterotrophic, move around environment • Funguslikeprotists: • slime molds and water molds • Plantlike protists: • can do photosynthesis
Characteristics • There are only a few general characteristics of protists • But most are characterized by body plan, how they obtain food, and motility • Unicellular or multicellular • Nutrition: can be autotrophic or heterotrophic • Motility: some move with cilia, flagella or pseudopodia
Reproduction • Most protists reproduce asexually using binary fission • Sometimes protists reproduce by multiple fission where one cell division produces more than two offspring • Protists that reproduce sexually via conjugation: • two cells join and exchange genetic material
Animal-Like Protists • These protists are divided into several Phyla: • Protozoa • Ciliophora • Sarcomastigophora • Apicomplexa • All of these protists are heterotrophic • They move around their environments and “capture” prey
Phylum Protozoa • Protozoa are single-celled protists that can move without cilia or flagella • There are more than 40,000 species of Protozoa • Most protozoa can form pseudopodia: large, rounded cytoplasmic extensions that function for movement and feeding • This movement is called ameoboid movement
Phylum Ciliophora • All ciliophora have cilia for movement • Cilia: short, hair-like projections that stick out of the cell membrane • This group includes the genus Paramecium, which are found in ponds and slow-moving streams • Ciliophora reproduces asexually and usually have two nucleii
PhylumsSarcomastigophora • All members of this phylum have one or more flagella • Flagella – long, whiplike structures that are made of microtubules and used for movement • Flagella help to move the protist rapidly through water • Many of these members are free-living in lakes and ponds • Some of these are parasites: Trypanosoma
Phylum Apicomplexa • Includes 4000 species whose adult forms cannot move • ALL apicomplexa are animal parasites: • Toxoplasma gondii • Plasmodium spp. • Cryptosporidium spp. • All apicomplexa have complex life cycle; most require two or more hosts to complete their life cycle
Plantlike and FunguslikeProtists • Plantlike protists includes algae and diatoms • These protists are autotrophic and have chloroplasts • Funguslikeprotists include slime molds and water molds • Like fungi, these protists have a stationary, spore bearing reproductive stage
Algae Phyla • Chlorophyta (green) – • More than 17,000 species, have chlorophyll/chloroplasts • Most are aquatic, can be unicellular or multicellular • Phaeophyta (brown) – • Mostly marine, includes seaweed and kelp • Rhodophyta (red)– • Contains chlorophyll a only, can live at deeper depths than other algea • Chrysophyta (golden) – • Most live in fresh water, have two flagella, have carotenoids
Diatoms and Dinoflagellates • Bacillariophyta (diatoms) – • 100,000 species are included in this phylum • All are unicellular, with cell walls • They are different shapes and are abundance in freshwater environments • Produce oxygen through photosynthesis • Dinoflagellata (dinoflagellates) – • These are small, usually unicelluarprotists with two flagella • They are photosynthetic, but a few species are heterotrophic • Some species of dinoflagellates use bioluminescence
Slime Molds • Includes about 700 species of plasmodial slime molds • Many slime molds have two nuclei that are not separated by a cell wall • Plasmodium reproduce when water is scarce, forming haploid spores by meiosis • In favorable conditions, two spores come together to form new plasmodium
Water Molds • Includes some protists that are parasitic (live in fish), also includes aquatic protists • Can reproduce sexually or asexually through zoospores • There is a possible link between one of the water mold phyla and fungi due to the amount of similarities
Protist and Human Interactions • Protists are typically microscopic, but they do play a very important role in the environment • Photosynthetic protists produce oxygen, some protists are essential parts of aquatic food chains, some protists play a role in the carbon cycle (respiration), and some protists have important symbiotic relationships • Protist populations can be influenced by temperature and nutrient availability – increase of both can cause algal blooms
Research • Protists have helped scientists understand fundamental cellular processes like movement • There have been many experiments aboutchemotaxis involving protists and their movement toward specific nutrients • This can help improve the treatment for some cancers and other diseases
Industry • Seaweed is used a food in Japan, Great Britain and some other Asian diets • We also use protist byproducts like alginate (used in cosmetics, various drugs, etc) • Carrageenan (red algae) is used in gelatin capsules and some types of cheese • Diatomaceous earth (from diatoms) is used in detergents, paint removers and some toothpastes
Human Diseases • Malaria – • Caused by Plasmodiumspp, trasmitted by mosquitos, enters blood stream and bursts red blood cells as well as liver cells • Giardiasis – • Caused by Giardia lamblia, caused severe diarrhea and intestinal cramps, transmitted through contaminated drinking water • Toxoplasma – • Caused by Toxoplasma gondii, transmitted through kitty litter, can be dangerous for developing fetuses and newborn babies
