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

• Funguslike protists:– 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

http://www.youtube.com/watch?v=7pR7TNzJ_pA

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

http://www.youtube.com/watch?v=a4aZE5FQ284

Phylums Sarcomastigophora

• 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 Funguslike Protists

• Plantlike protists includes algae and diatoms• These protists are autotrophic and have

chloroplasts• Funguslike protists 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 unicelluar protists 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 about chemotaxis involving protists and their movement toward specific nutrients

• This can help improve the treatment for some cancers and other diseases

http://www.youtube.com/watch?v=8AghW4zzbhU

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 Plasmodium spp, 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

http://www.youtube.com/watch?v=-zsdYOgTbOk