Protists : Protists Protists are single celled eukaryotes. A few forms are multi-cellular.
Protists often have a very complicated internal structure: a single cell must do all the functions that we have many different cell types to do.
Protists can be divided into plant-like, fungus-like, and animal-like forms. This division probably has little to do with their evolutionary history. Protist Phylogeny : Protist Phylogeny Protists are very diverse, and probably represent several different evolutionary lineages, more distinct from each other than plants, animals, and fungi are. Animal-like ProtistsProtozoans : Animal-like ProtistsProtozoans The animal-like protists are classified according to how they move: amoeba-like, ciliated, or flagellated.
Amoeba-like protists move by extending pseudopods, part of their cytoplasm, then pulling the rest of the cell along behind. They can surround and engulf their food this way.
Some amoeba-like protists have hard shells. The foraminiferans are covered in calcium carbonate—chalk, which we use on chalk boards. Amoebas in Action : Amoebas in Action Ciliated Protists : Ciliated Protists Cilia are small hairs surrounding the protist’s body. The cilia beat in a synchronized pattern to cause movement.
Paramecium is a typical ciliate. It has a gullet to swallow food, and a contractile vacuole to get rid of excess water.
Genetics: the DNA used for sexual reproduction is stored in the small micronucleus. A copy of this information is used to run the cell: the copy is kept in the much larger macronucleus. Flagellates : Flagellates Flagellates have a small number of long flagella, long whiplike hairs that beats to propel the cell.
Some nasty parasites are flagellates, including Giardia lamblia, which causes diarrhea and which is found in most of the surface waters of the US. Another is Trypanosoma brucei, which causes sleeping sickness in Africa. Also Trichmonas vaginalis, a sexually transmitted disease. Sporozoans : Sporozoans Sporozoans are animal-like protists that have part of their life cycle inside the cells of their hosts.
The most important example is Plasmodium, the parasite that causes malaria. Malaria kills 1-2 million people each year.
Mosquitoes are part of the life cycle. They suck blood from infected humans, ingesting the sporozoans. The sporozoans undergo sexual reproduction in the mosquito’s gut.
When the mosquito bites another person, the sporozoans infect the blood and liver of the host. The parasites multiply asexually inside the red blood cells, destroying them as they leave. Interactions with Organisms : Interactions with Organisms Symbiosis: A close relationship between two organisms where at least one organism benefits.
Ex: The protist that lives in the stomach of a termite helps to digest the wood the termite eats. The protist gets a source of food and the termite digests the wood better.
Mutualism: A type of symbiosis where both partners benefit from living together.
Parasitism: A relationship where one organism benefits from another at the other’s expense.