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