Protists

Protists Eukaryotic organisms that cannot be classified as fungi, plants, or animals Many important characteristics evolved in protists Membrane-bound organelles Allow cells to perform a variety of functions Complex cilia and flagella Found in organs of other organisms (lungs) Sexual reproduction with gametes Allows greater genetic diversity Multicellularity Allows cells to be able to specialize

Protists Reproduction Protists can reproduce in two ways: Asexual reproduction Results in offspring genetically identical to parent Sexual reproduction Results in offspring genetically different from parents

Asexual Reproduction Binary Fission—occurs when a unicellular organism reproduces by splitting in half after copying its DNA Similar to mitosis in multicellular organisms Budding—occurs when part of the parent organism pinches off to form a new organism New organism is smaller than parent organism Can occur in unicellular & multicellular organisms Fragmentation—similar to budding; occurs only in multicellular organisms, and happens by accident

Sexual Reproduction Occurs as a response to environmental stress Unicellular organisms (called zygospores) reproduce through meiosis and release haploid cells that mature Multicellular organisms have an alternation of generations Diploid, spore-producing phase called sporophyte generation Produce haploid spores by meiosis

Sexual Reproduction, cont. Haploid, gamete-producing phase called gametophyte generation Produces gametes through mitosis Two gametes fuse to form a diploid zygote which is the first stage of the new sporophyte generation

Classifying Protists Organisms classified as protists likely to change as scientists learn more about how they are related to each other and members of other kingdoms Molecular studies provide lots of information about relationships Characteristics shared with plants, animals, and fungi provide evolutionary information New classification system for protists being developed

Groups of Protists Grouped by the way they obtain nutrition Divided into three groups: Plant-like (photosynthetic) Animal-like (heterotrophic) Fungus-like (absorb nutrients from the environment & reproduce by releasing spores)

Animal-Like Protists Called protozoa which means first animal All are unicellular, most can move, and most reproduce asexually by binary fission Four groups: Amoeboid Protists Ciliates Flagellates Sporozoans

Amoeboid Protists Move using pseudopodia which are also used to surround and engulf food Live in fresh water, salt water, and soil Can be parasitic Some form tests Outer shells made from protein, calcium carbonate, silica, or mineral particles

Ciliates Have a tough, flexible covering and short, hair-like structures called cilia Move and hunt food by beating cilia Live in fresh water and salt water Reproduce sexually through conjugation

Flagellates Have whip-like structures called flagella Can have cilia or form pseudopodia Many free-living, but can be parasitic (Leishmania)

Sporozoans Do not move Parasitic and cause disease Reproduce asexually and sexually Form spore-like cells

Plant-Like Protists Include organisms commonly called phytoplankton and algae Vary in types of pigments used for photosynthesis and types of molecules used to store energy Six groups: Diatoms Euglenoids Dinoflagellates Red Algae Brown Algae Green Algae

Diatoms Unicellular protists with double shells Shells made of silica or calcium carbonate Diploid and reproduce asexually Get smaller each generation At a certain size, they go through sexual reproduction to produce full-size offspring

Euglenoids Freshwater protists with one or two flagella Most photosynthetic; some photosynthetic and heterotrophic; some others completely heterotrophic Some have eyespots Light-sensitive organs that help them move toward light

Dinoflagellates Unicellular protists that typically have two flagella Most photosynthetic, but some are heterotrophic Most have protective cellulose coats that become encrusted with silica This gives the unusual shapes Flagella beat in two grooves One around organism like a belt; one perpendicular Causes the organism to spin like a top

Red Algae Multicellular, found in warm ocean waters Absorb blue light, allows them to grow at greater depths Some have calcium carbonate in their cell walls Play important role in the formation of coral reefs

Brown Algae Multicellular, found in cool ocean waters Kelp with root-like structure (holdfast), stem-like structure (stripe), and leaf-like structures (blades) Only algae that form more than one tissue type

Green Algae Closest to plants and are believed to have given rise to the first true plants Do not have complex tissue layers This is why they are not classified as plants now May be classified as plants in the future

Fungus-Like Protists Once classified as fungi, but molecular information proved that to be false Broken into two groups: Slime Molds Water Molds & Downy Mildews

Slime Molds Exist as single-celled amoebas under normal conditions Form colonies and release spores in harsh conditions Help researchers understand how cells interact and how cytoplasm moves within cells

Water Molds & Slimy Mildew Form multicellular filaments that resemble fungi Many decompose dead organism Others are parasitic Water mold responsible for the Great Potato Famine of 1846 Downy mildew responsible for the poor grape harvest in the French wine country in 1879 (almost wiped out the industry)

Protists & Disease Parasitic protists cause many diseases, sometimes death, in humans Giardiasis Amebic Dysentery Toxoplasmosis Trichomoniasis Cryptosporidiosis Chagas Disease Malaria

Giardiasis Causes severe diarrhea & intestinal cramps Contracted by drinking contaminated water Lasts 2-6 weeks; rarely fatal

Amebic Dysentery Caused by parasite Entamoeba histolytica Amebiasis—mild form, lasts a couple weeks Amebic dysentery—sever form; causes pain, bloody diarrhea, & fever In rare cases, amoebas travel to liver, lungs, or brain & can be fatal Transferred in contaminated water & raw fruits/vegetables washed in contaminated water

Toxoplasmosis Causes flu-like symptoms Spread by cats & by eating undercooked meat Healthy adults usually not affected Can cause nerve, brain, or eye damage in rare cases Babies of pregnant women more susceptible Can cause nerve, brain, or eye damage in fetus Wash hands & cook meat thoroughly

Trichomoniasis Most common STD; caused by Trichomonas vaginalis Infects about 7.4 million people each year Causes discolored urine, itching, and sometimes vaginal secretions Not fatal; can be treated with medicine

Cryptosporidiosis Causes severe cramps & diarrhea Lasts about two weeks Spread by contaminated water/objects & uncooked food People with weak immune systems can suffer longer

Chagas Disease Also called American trypanosomiasis Occurs in South & Central America Early stage has few or no symptoms Chronic stage can cause heart disease, abnormal heartbeat, heart failure, heart attack, & enlargement of the esophagus & large intestines

Malaria Caused by sporozoans of the genus Plasmodium Infects the liver and red blood cells Can cause rupture of the spleen, kidney failure, coma, brain damage, & death if left untreated

Protists & the Environment Plant-like protists produce oxygen & take up carbon dioxide during photosynthesis Others help decompose dead organisms which helps to recycle nutrients Photosynthetic protists form the base level of almost all aquatic food chains Protists produce algal blooms that can be harmful to humans & other organisms About 15% of species on Earth are symbiotic protists

Protists & Industry Used in food production Ice cream, salad dressings, gelatin Used for industrial & consumer products Agar, paint, fire-fighting foam, toothpaste, makeup Used in scientific research Used to study ribosomes, cell aging, & cell cycle control Used to study cell movement & signaling Help researchers understand how white blood cells fight disease