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Protista







  

Protist Page

Welcome to the wonderful world of protista! We're glad you stopped by, feel free to look around. We've added all new, totally origional material to the site, and we think its the best we've done so far. Plus, there is a brand new feature! We found a protist who wants to publish his live journal on our website, and he's a fascinated Euglena, named Eugine. Please check it out!

Click here to read the journal of a protist, hear his innermost thoughts, and read as his journey to discover his true identitiy unfolds!

The kingdom Protista is a might bit confusing to the laymen. We will try and do our best to make this kingdom easy to understand. Protists can best be understood by thinking about them as the Kingdom of simple eukaryotes (eukaryotes have nuclei). Protists have membrane-bound organelles and a defined nucleus. Many scientifically inclined people get the need to organize this kingdom a bit more than just saying "They all have a nucleus. Thats it - thats what they are!". These are very smart scientifically inclined people, and they worked very hard to split them into three general parts. These parts are algae, protists and slime molds. (Funny though, how in the kindgom protista, there is a division of protist. But whatever, we'll go with it.)

*Algae* are plant-like photoautotrophs (lets break that word down, photo meaning they derive energy from light, auto meaning self, and troph meaning food. All that in mind, photoautotroph must mean that they derive energy from light by themselves. Which is exactly correct.) and have cell walls. Algae are difficult to define (much like all protists), and several different classification systems exist (See, scientifically inclined people all think differently. They like to confuse Bio 2 AP students.) On this website, and like most scientifically inclined people in general, we will treat all eukaryotic photoautotrophic microorganisms as algae. This includes five groups: green algae, red algae, brown and yellow-brown algae, dinoflagellates, and euglenoids. Algae are extremely important as producers in the world's oceans and lakes. You may even find algae in your local fish pond.

*Protozoa* are animal-like. Protozoa lack cell walls and are eukaryotic (we went over this, remember? check above and make sure you know what this means!) heterotrophic (hetero - outside sources, trophic - food. Lets break it down like last time, this means they get food from outside sources) microorganisms. They include ciliates, kinetoplastids, and sarcodina. Many protozoa live as parasites within other animals.


*Slime molds* are unusual microorganisms that resemble protozoa (the classification described above)at some phases of their life cycles and fungi at other phases. The two groups of slime molds, cellular and acellular, are not closely related. Slime molds live in damp soils and decaying plant material.


We also are going to include a preassembled list of some vocabulary words that scientifically inclined people associated with protista, and thier definitions, to make your reading easier:

Alternation of generations - A reproductive strategy that involves a succession of haploid and diploid phases.


Ameboid motion - Type of motion in which cytoplas can flow beneath the cell membrane into new branches called pseudopods, helped by filaments of a structural protein called actin, causing the cell to move in a given direction.


Cilia - Short hair-like projections found on eukaryotic cells that can help the cell move or can sweep food particles toward the mouth.


Chlorophyll - The pigment found in green plants and algae that allows them to undergo photosynthesis


Chloroplasts - The organelles in which photosynthesis takes place in green plants and algae.


Endosymbiotic theory - This theory states that eukaryote organelles may have evolved when large eukaryotic organisms engulfed but did not digest smaller organisms and a symbiotic relationship arose.


Isogamus - An organism that has only one type of gamete rather than separate male and female gametes.


Macronucleus - In ciliates, the large nucleus that holds many copies of the cells genetic material. It is responsible for the growth and metabolism of the cell.


Micronucleus - In ciliates, the smaller nucleus responsible for the transmission of genetic material during sexual reproduction.


Oral groove - In ciliates, the membrane structure that functions in food uptake.


Pinocytosis - Method of food uptake in which a liquid or small food particle is sucked into an invagination in the cell membrane, which then folds in on itself and pinches off from the cell membrane to become a small vacuole.


Phagocytosis - Method of food uptake in which a flexible portion of the cell membrane surrounds a food particle and engulfs it, bringing it into the cell in a vacuole. Phagocytosis is used to ingest other unicellular organisms or large particles.


Photosynthesis - The process in which some organisms can use the energy of light to transform inorganic materials into usable organic materials.


Plankton - Small free-floating organisms in fresh- and saltwater that are a major marine food source.


Plasmodium - The diploid vegatative phase of acellular slime molds


Pseudoplasmodium - The haploid slug-like phase of cellular slime molds that gives rise to the fruiting body.


Pseudopods - Temporary cytoplasmic protrusions of ameboid cells that function in movement and food uptake by phagocytosis.


Stigma - The light sensative region in euglenoids that allows them to move toward light sources.


Thallus - The leaf-like bodies of algae.


Vacuole - A membrane bound portion of the cell usually used for holding materials such as food and waste.

Characteristics

Protists are the most nutritionally diverse of all eukaryotes. Most use mitochondria for cellular respiration. Yet, few do not have mitochondria and either live in anaerobic environments or contain mutualistic respiring bacteria. Some protists are photoautotrophs with chloroplasts, some are heterotrophs that absorb or ingest food, some are mixotrophs which use photosynthesis and heterotrophic nutrition. All algae have clorophyll a, the pigment found in plants, but they differ in the fact that they have accessory pigments that trap wavelenghts of light to which chlorophyll a is not sensitive to.

Protists move by use of flagella or cilia during some part of their lives. Eukaryotic flagella and cilia extend from the cytoplasm. Microtubules covered by a plasma membrane cover them. Flagella and cilia are similar in function, but cilia are shorter and larger in number.

The reproductive and life cycles of protists vary greatly. They may reproduce sexually or asexually, sometimes both during certain stages of life. Mitosis occurs in most protists, but there are variations that differ from other eukaryotes. Some go through the process of syngamy, which is the shuffling of genes between two individual cells that reproduce asexually afterwards. During the life of several protists, resistant cells called cysts that survive harsh conditions are formed.

Protists live in wet environments and often anywhere there is water. Some may live in damp soil as well, or leaf litter and moist terrestrial habitats. Many stay at the bottom of bodies of water and attach to rocks and other things that may creep through the sand or silt. Protists also make up plankton, which are groupings of organisms that easily drift along the water's surface.

Some protists are involved in symbiotic relationships, living in body fluids, tissues or cells of hosts. These relationships may be mutualistic or parasitic, and anywhere in between.


Nutrition for Protista

Nutrition for protista is a bit complicated, but what else is new? Different classifications derive food differently. The classification Protozoans means that all organisms classified with protists ingest their food, and thus they live primarily in aquatic habitats, such as ponds, drops of water in soil, or the digestive tracts of animals. The second group, the slime molds feed on bacteria for food, and when when sufficient bacteria is present, cellular slime molds are single amoeboid cells; however, when food becomes scarce, they aggregate into sluglike colonies, which become large reproductive structures. Plasmodial slime molds also exist as single cells when nutrients are plentiful, but each cell can grow into a large, branching plasmodium, with many nuclei and a continuous nucleus. This differentiates into reproductive structures when food is short. The third and fourth groups of protists, the algae, contain chloroplasts and photosynthesize like plants.

Reproduction (i'd do a cliche sex joke here, but its just not coming to me.)

This is the sex part of our presentation, and since sex is something our class often gets very excited about (that and falic symbols) we will try and go into some depth about protist sex. Protists can reproduce mitotically, and some are capable of meiosis for sexual reproduction. Mitosis is normal cell division, it includes the replication of DNA, and then normal cell division. Meiosis is the replication of sex cells, therefore designed to create gametes. They are haploid cells. Protists reproduce both ways, depending on the need.


***********The MOST EXCITING THING WE HAVE EVER DONE EVER having to do with meiosis and mitosis is on the website http://www.colorado.edu/epob/academics/web_resources/cell_division/ YOU MUST TO GO TO THAT SITE! GO! GO! GO! Its beautifully animated, and so excitingly interactive. LOVE IT! *****************


 

Examples and Pictures of the Kingdom are located on the picture page located on the left hand side of your screen! These are some links to copy into your browser's address box, and check out!

PROTIST WEBSITES! (oh so much fun!)

http://biog-101-104.bio.cornell.edu/BioG101_104/tutorials/protista.html

Go here to see protists in action!

The who am i? protist page - a definite winner, check it out.

http://www.knossos.org/knossids2001/protistgame.html

protist HANGMAN - almost good enough to go in the game section. (but not quite...)

http://www.knossos.org/knossids2001/hangman.html



 

Divisions of Protista

Phylogeny is a classification system resembling a family tree. Systematists have been working on the Kingdom Protista for a number of years, and are still debating the proper way to divide the kingdoms to this day. Some systematizes consider Kingdom Protista and the five-kingdom system outdated. Earlier, we introduced the popular eight-kingdom system that recognizes three protist kingdoms (Archaezoa, Protista, and Chromista). However, Kingdom Protista, in both the five-kingdom and the eight-kingdom systems are polyphyletic, meaning members come from two or more ancestral forms not common to all members. Therefore, being polyphyletic, Protista classifications go against phylogeny.



But don't worry! Here, we will break down Protista into five candidate kingdoms, because each deserves kingdom status, but has not quite made it, due to the debate that has ensued for so long. So let's pretend that we are dealing with a classification system where plants, animals and fungi are separated into their own kingdoms. We are missing the Protista section on the phylogenic chart. The five candidate kingdoms are:

Archaezoa,

Euglenozoa,

Alveolata,

Stramenopila,

and Rhodophyta.

Members of the candidate kingdom Archaezoa lack mitochondria and may represent early eukaryotic (organisms with a nucleus) lineages. Both the eight-kingdom system and the candidate kingdom plan place protists lacking mitochondria (an organelle in eukaryotic cells that hosts cellular respiration, also known as the power house of the cell) together in the kingdom Archaezoa, whose name comes from the Greek word “arkhaios," meaning “ancient." Archaezoa have three subgroups: diplomonads, trichomonads, and microsporidans. Diplomonads have flagella (reviewed earlier in the vocabulary section), two separate nuclei, no mitochondria, no plastids (organelles that are closely related to plant organelles, including chloroplasts), and a simple cytoskeleton. An example of a diplomonad is a parasite called Giardia lamblia, which infects human intestines. Archaezoa is the most controversial of all the kingdoms, because evolutionary relationships between the three sub groups have not yet been agreed on by scientists.

Candidate kingdom Euglenozoa includes both autotrophic and heterotrophic flagellates, which are protists with flagella. The two subgroups under Euglenozoa are euglenoids and kinetoplastids. The flagella of euglenoids come out of a pocket or chamber on their outside. They also have storage molecules called paramylum (a glucose polymer). Euglenoids are mostly autotrophic, but may also be heterotrophic (they absorb organic molecules from surroundings, or ingest prey). Kinetoplastids have a big mitochondrion that houses extranuclear DNA (not enclosed in the nucleus). They are involved in symbiotic relationships and may be harmful to hosts. An example of a kinetoplastid is a species of Trypanosoma, which causes African sleeping sickness.

Candidate kingdom Alveolata includes a group of photosynthetic flagellates called dinoflagellates, a group of parasites, and a group of ciliates (like flagellates, but these organisms move using cilia). Characteristics of Alveolates are that they have alveoli, which are small membrane-bound cavities under their surfaces. It is unknown if alveoli have specific functions, but they may help regulate the cell surface and the cell's water. The three sub groups of Alveolata are dinoflagellates, apicomplexans, and ciliates. Dinoflagellates float near the water's surface and provide foundation for many marine and freshwater food chains. They are made of phytoplankton. If you ever see red tides, you will know that it is a result of dinoflagellates, because they have a reddish tint. Although pretty, this type of tide may be very dangerous to fish, invertebrates and humans. Most dinoflagellates are unicellular and have characteristic shapes, with flagella that cause them to spin. Dinoflagellates divide during asexual repoduction and have an unusual nucleus. Dinoflagellates are very diverse; some live with animals such as jellyfish that build coral reefs, some serve as the main food source for communities of reefs, some are parasitic and feed off of marine animals, if they do not have chloroplasts and are unable to photosynthesize. They may be heterotrophic or may be temporarily autotrophic. Apicomplexans are parasitic and feed off of animals, sometimes causing serious disease when they become sporozoites (infections microscopic cells). One end of the sporozoite is made up of complicated organelles designed to penetrate the hosts cells. These organisms are sexual or asexual, and require at least two hosts to complete life cycles. An example of an apicomplexan is a plasmodium, the parasite that causes malaria (a disease spread by mosquitoes). Ciliates are characterized by cilia, which help them to move and eat. Cilia may be compared to flagella in the way they both work, but cilia are shorter. Ciliates usually live in fresh water. The cytoskeletons makeup and the makeup of the cell's outer layers of cytoplasm provide information that tells the cilia how to organize themselves. Ciliates differ greatly; some are covered with rows of cilia, while some have clusters of cilia. Some scurry on “legs" made of cilia, and some have cilia that functions as locomotor membranelles. Ciliates are the most complex of all cells. They have two types of nuclei; a large macronucleus and several small micronuclei, each with specific functions relating to genes and everyday functions of a cell.

Candidate kingdom Stramenopila is very diverse. It includes several types of photosynthetic autotrophs (also known as algae), and groups of heterotrophs. What does the term stramenopila mean? It refers to tiny hairlike mechanisms coming out of the flagella that each of the organisms in this candidate kingdom have. Some stramenopila are heterotrophic, while the photosynthetic stramenopila have chloroplasts containing two membranes outside the chloroplast envelope, a small amount of cytoplasm, and a vestigal (it is not used for anything) nucleus. There are four sub groups within kingdom Stramenopila, being Diatoms, Golden algae, Brown algae and water molds. Diatoms are yellow or brown, and have unique walls made of hydrated silica in an organic matrix. Think of a wall made of glass. Each has two overlapping parts (think shoe box and lid), and they are able to glide due to interactions in the cytoplasm between actin and filaments. Diatoms reproduce asexually for most of the year by mitosis (cell division). Sexual reproduction is uncommon in that it requires the formation of eggs and sperm. Diatoms are plentiful in freshwater and marine plankton. Golden algae are gold in color because of a mixing of yellow and brown pigmints. Their cells usually have flagella near one end of the cell. They live in freshwater and marine plankton. Some absorb dissolved organic compounds or ingest food particles or bacteria. Most are unicellular. Water molds are also known as oomycotes, or white rusts and downy mildews. All are heterotrophic stramenopiles, and all do not have chloroplasts. Some are unicellular, and others are made of hyphae (filaments that look like a cluster of branches). Water molds have cell walls made of cellulose (they are different than fungi in that way, because the cell walls of fungi are made of chitin). Oomycota means “egg fungi," referring to sexual reproduction. Large egg cells are fertilized by small sperm nuclei. Most water molds are decomposers that grow on dead algae and animals, mostly in fresh water. Some may be parasitic, for example, water molds that grow on the skin and gills of fish, but only feed on injured tissue. On land, these organisms live off of plants. They are dispersed in spores (windblown) or flagellated zoospores. Brown algae is the largest and most complex algae. They are all multicellular and mostly marine. They are most common along temperate coasts, where the water is of a cool temperature. Seaweed is often brown algae. Red algae and green algae include seaweed as well.

Red algae of the kingdom Rhodophyta lack flagella. Red algae are not ancient; flagella was lost during evolution. Red algae are reddish in color because of pigmentation. Not all rhodophytes are red; species adapt to water depths differ in color. Some rhodophytes may be black in deeper water. Some do not have pigments at all, and live by being parasitic and feeding off of other organisms. Red algae are most common in coastal waters warm in temperature. Most are multicellular, and some share seaweeds with brown algae, although the red algae is not as large as the brown algae. The life cycles of red algae are very diverse. They lack flagella, and gametes rely on watter currents to join.

Green algae are green in color. As evidenced by molecular systematics, green algae and plants are very closely related. Some systematists even would like to see green algae classified as plants. There have been over 7000 species of green algae identified. Most live in fresh water, but may be marine as well. Some are unicellular and live as plankton or in wet soil or snow. Some live in symbiotic relationships with other eukaryotes. An example is a chlorophyte, that lives symbiotically with fungi in mutualistic collectives called lichens. Most green algae have sexual and asexual reproductive stages, but nearly all reproduce sexually with biflagellated gametes with cup-shaped chloroplasts. Some, however, conjugate (transfer DNA directly from one cell to another), such as the spirogyra.



 

Its what everyone's been waiting for.... GAME TIME

Now, you all are thinking, this is the space on the page where Katie would normally would put a game... what game could she possibly find to relate to protists? Well, never fear my friends, creativity is here! Pac-man is my game of choice. Scientists, when looking at protists usually arent sure how to deal with them. They think to themselves "How will I catagorize this? What exactly is this? I really dont know!" that is also exactly what a layman would think when looking at pac-man. Is he uni-cellular? Is he multi-cellular? Does he photosynthesize? We dont really know. All we know is that he runs from monsters and eats dots... That doesnt really tell us much. So, my dear friends, play pac-man, and wonder, what KIND of creature is he? Until we know, we will say, "ahh, it doesnt matter, he's a protist!"

Now, I present to you: PAC-MAN THE PROTIST-