Protists

  The kingdom Protista (which means “the very first” in Greek) contains over 200,000 diverse species .
 * Introduction **

 Any eukaryote that is not a member of the kingdoms Plantae, Animalia, or Fungi is a protist.  Most protists are unicellular, but a few consist of hundreds or thousands of cells.  The first eukaryotes on Earth 1.5 billion years ago were protists.  The first protists may have evolved from a symbiosis of several cells. Mitochondria and chloroplasts may have evolved from aerobic and photosynthetic prokaryotes that began living inside larger cells.  Many biologists want to split protists into several kingdoms. Recent DNA evidence revealed that different groups of protists evolved independently from archaebacteria.  Protists can be classified according to how they consume nutrients. Heterotrophic protists are labeled animallike, photosynthetic protists are plantlike, and those that use external digestion are called funguslike protists.  Heterotrophic, animallike protists are called Protozoans.  Protozoans are divided into four phyla by their means of movement. Zooflagellates swim with flagella, sarcodines move by expanding their cytoplasm, ciliates move using cilia, and sporozoans are not capable of movement.
 * Protozoans **

// Zooflagellates //  Zooflagellates, of the phylum Zoomastigina, use long whiplike flagella to move through aquatic environments.

 They absorb food through their cell membranes. Some consume organic wastes out of water, and others live inside host organisms which supply them with food.  Most zooflagellates reproduce by binary fission, but some produce gametes and have a sexual lifecycle. // Sarcodines //  Sarcodines, of the phylum Sarcodina, use temporary projections of cytoplasm called pseudopods for feeding and locomotion.

 Amoebas, a sarcodine, have thick pseudopods which they fill with cytoplasm to move. They surround food particals and take them in through endocytosis, creating a food vacuole. They reproduce by binary fission.

<span style="font-size: 12pt; font-family: Wingdings; mso-list: Ignore; msofareastfontfamily: Wingdings; msobidifontfamily: Wingdings; msolist: Ignore;"> Foraminiferans, another sarcodine, live in warm regions of the ocean. When they die their calcium carbonate shells form chalky deposits on the ocean floor. <span style="font-size: 12pt; font-family: Wingdings; mso-list: Ignore; msofareastfontfamily: Wingdings; msobidifontfamily: Wingdings; msolist: Ignore;"> Heliozoans (meaning “sun animal”) produce silica shells which look like the sun’s rays. // Ciliates // <span style="font-size: 12pt; font-family: Wingdings; mso-list: Ignore; msofareastfontfamily: Wingdings; msobidifontfamily: Wingdings; msolist: Ignore;"> Ciliates, of the phylum Ciliophora, use short hairlike projections similar to flagella called cilia for locomotion. They live in both fresh and salt water mostly independent of other organisms.

<span style="font-size: 12pt; font-family: Wingdings; mso-list: Ignore; msofareastfontfamily: Wingdings; msobidifontfamily: Wingdings; msolist: Ignore;"> Ciliates feed by using their cilia to sweep foor particles into an indentation called the gullet which creates food vacuoles. These food vacuoles then fuse with lysosomes which break the nutrients down. The food vacuole then fuses to a part of the membrane called the anal pore to release waste. <span style="font-size: 12pt; font-family: Wingdings; mso-list: Ignore; msofareastfontfamily: Wingdings; msobidifontfamily: Wingdings; msolist: Ignore;"> Ciliates normally reproduce by means of binary fission, but when under stress they can share genes through a process called conjugation. Two organisms connect and their micronuclei divide into four by meiosis. Then three of the resulting micronuclei are destroyed and the fourth is divided into two my mitosis. They then exchange one of their identical micronuclei. At the end of conjugation both individuals are genetically different than they originally were. // Sporozoans // <span style="font-size: 12pt; font-family: Wingdings; mso-list: Ignore; msofareastfontfamily: Wingdings; msobidifontfamily: Wingdings; msolist: Ignore;"> They reproduce by means of sporozoites which penetrate host cell and live with in them as a parasite.

// Disease // <span style="font-size: 12pt; font-family: Wingdings; mso-list: Ignore; msofareastfontfamily: Wingdings; msobidifontfamily: Wingdings; msolist: Ignore;"> Malaria is caused by the sporozoan //Plasmodium// which is carried by the female //Anopheles// mosquito. It kills 2 million people a year and infects hundreds of times more.

<span style="font-size: 12pt; font-family: Wingdings; mso-list: Ignore; msofareastfontfamily: Wingdings; msobidifontfamily: Wingdings; msolist: Ignore;"> When an infected mosquito bites someone, its saliva carries sporozoites into the blood which then infect liver and blood cells. When infected blood cells burst they release toxins into the body causing symptoms. <span style="font-size: 12pt; font-family: Wingdings; mso-list: Ignore; msofareastfontfamily: Wingdings; msobidifontfamily: Wingdings; msolist: Ignore;"> Chloroquinine is effective against malaria but some strains of //Plasmodium// are resistant to it. Controlling the mosquitoes is most effective. <span style="font-size: 12pt; font-family: Wingdings; mso-list: Ignore; msofareastfontfamily: Wingdings; msobidifontfamily: Wingdings; msolist: Ignore;"> // Trypanosoma // is another infectious protist. Spread by tsetse flies, it causes fevers and rashes as well as nerve damage which can lead to a fatal coma. <span style="font-size: 12pt; font-family: Wingdings; mso-list: Ignore; msofareastfontfamily: Wingdings; msobidifontfamily: Wingdings; msolist: Ignore;"> // Entamoeba // living in contaminated water cause amoebic dysentery by attacking the intestine wall and causing bleeding and severe diarrhea. <span style="font-size: 12pt; font-family: Wingdings; mso-list: Ignore; msofareastfontfamily: Wingdings; msobidifontfamily: Wingdings; msolist: Ignore;"> // Giardia // is another pathogen that can be found in streams. It creates microscopic cysts which cause diarrhea and digestive problems. // Ecology // <span style="font-size: 12pt; font-family: Wingdings; mso-list: Ignore; msofareastfontfamily: Wingdings; msobidifontfamily: Wingdings; msolist: Ignore; msobidifontstyle: italic;"> Protozoans play an important role in ecology. They interact symbiotically with other organisms, decompose organic matter, and are food for larger animals. <span style="font-size: 12pt; font-family: 'Times New Roman'; mso-fareast-font-family: 'Times New Roman'; mso-font-kerning: 14.0pt; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA;"><span style="font-size: 12pt; font-family: Wingdings; mso-list: Ignore; msofareastfontfamily: Wingdings; msobidifontfamily: Wingdings; msolist: Ignore; msobidifontstyle: italic;"> An example of symbiosis, //Trichonympha// is a zooflagellate which breaks down cellulose inside a termites body allowing it to eat wood.