Biology 112

Includes more than 200,000 species Easier to classify protists by what characteristics they don’t possess It is not a plant, animal, fungi, or prokaryote They are eukaryotic cells that contain a nucleus and membrane-bound organelles They are mainly unicellular but are also multi- cellular

They were the first eukaryotic organisms on Earth Appeared nearly 1.5 billion years ago Probably evolved from a symbiosis of several cells

One possible way is how they obtain their nutrition Heterotrophs are animal-like protists Autotrophs are plant-like protists External digesters (decomposers and parasites) are fungus-like protists A shortcoming of this classification is that it does not reflect their evolutionary history

Classified according to their movement Zooflagellates (Phylum Zoomastigina) Possess flagella, which are whip-like structures used for movement through water May have one to many flagella Absorb food through their cell membranes Reproduce asexually by mitosis and cytokinesis or sexually though meiosis where two organisms fuse together and produce a new organism with a recombination of genetic material

Sarcodines (Phylum Sarcodina) Possess temporary cytoplasmic projections called pseudopods for both movement and feeding Most common example are amoeba Cytoplasm moves into the pseudopods and propels the organism forward Amoeboid movement Encapsulate their food and form a food vacuole digested food is used by the cell and undigested remains in vacuole until it can be eliminated Reproduce by mitosis and cytokinesis

Ciliates (Phylum Ciliaphora) Contain cilia, short hair-like structures similar to flagella used for movement and feeding Found in both salt and fresh water Most are free-living and do not exist in symbiotic relationships Paramecium are the most common ciliates They contain trichocysts below their surface Stiff projections that can be released which will protect the cell Possess two nuclei – macronucleus and micronucleus Macronucleus contains exact copies of genetic information responsible for daily function Micronucleus contains a reserve copy of all the cell’s genes

Sweep food with cilia into a gullet, an indentation on the side of the organism Food gets trapped and absorbed into a food vacuole Waste material gets fused with an anal pore Water moves into the organism through osmosis Excess water moves into contractile vacuoles which is then expelled by the organism

Most reproduce asexually through mitosis and cytokinesis While experiencing an external stress, may reproduce by conjugation Two organisms fuse together and exchange genetic information once they undergo meiosis This is not technically reproduction since no new organisms are produced Only new combination of genetic material occurs It is referred to as a sexual process instead

Sporozoans (Phylum Sporozoa) Do not move on their own and are parasitic Found in many different organisms Many times, they have more than one host They reproduce by sporozoites