ProtistaRachel Lloyd

An image of kelp, the largest known type of protist. Kelp is often found in colonies called “kelp forests”, as shown above. (JS) (21)
An image of kelp, the largest known type of protist. Kelp is often found in colonies called “kelp forests”, as shown above. (JS) (21)


DIAGNOSTIC CHARACTERISTICS OF THE GROUP
Protists tend to be single-celled eukaryotes although some are multicellular organisms such as seaweed. The main characteristic that makes protists different from any of the other eukaryotic kingdoms is that they aren’t true plants, animals, or fungi.
Most protists are able to move. They usually have flagella or cilia at some point in their life time. Both flagella and cilia being used for movement of the cell, but cilia as shorter than flagella and there are more of them. Flagella differ for prokaryotes and eukaryotes. A prokaryote’s flagella are attached to the cell surface, and a eukaryote’s flagella extend from the cytoplasm as bundles of microtubules covered by the plasma membrane.
Protists vary in their ways of obtaining nutrients and energy. Protists can be heteratrophs; autotrophs; or mixotrophs, organisms that use photosynthesis and heterotrophic methods to obtain nutrients and energy. Most use mitochondria for cellular respiration.
Protists can be broken down into three categories: ingestive protists, or protozoa, which are animal-like protists; absorptive protists, which are fungus-like protists; and photosynthetic protists, or algae, which are plant-like protists.
Fungus-like and animal-like protists are hereotrophs. However, fungus-like protists have cell walls and can reproduce by creating spores but, animal-like protists cannot. Animal-like protists are put into groups based on how they live and move. All animal-like protists are unicellular. Unlike fungus-like and animal-like protists, plant-like protists are autotrophic. In addition plant-like protists can be multicellular, unicellular, or live in a colony. (4)(MF)
[The cell walls of Protists are used as additives in food. In red algae the cell wall is made up of agar and carageenan. Agar is used as a gelling agent and thickener. In brown algae, cell wall of algin and cellulose protects them against waves and exposure to air (component ensures uniform freezing and melting of foods). The cell walls in Fungi are composed of cellulose or chitin. (MP) 16]



HABITATS
Protists live where there is water whether that is in an ocean, pond, or lake; or a terrestrial environment with enough moisture. In bodies of water many protists are bottom dwellers. Other protists live near the surface of the water. Another place some protists live is within hosts, specifically in the body fluids of the hosts. Bottom dwellers and other protists that attach themselves to non-floating aquatic surfaces, such as rocks, are known as benthic protists. Protists that float within these bodies of water are known as planktonic protists. (CSR, 5)


MAJOR TYPES
Protists are catergorized into three (unofficial groups) based on how they consume/produce energy. There are animal-like protists that feed by phagocytosis, photosynthetic protists (algae) and fungus-like protists that feed by absorption. (AC)(20)
Diplomonadida
Diplomonads lack mitochondria along with parabasalids. They also have multiple flagella, two nuclei, a relatively simple cytoskeleton for a eukaryote, and no plastids.
Some diplomonads are free-living and live in fresh water. However, most are parasitic in animals. Some can cause disease in humans. For example, Giardia can cause diarrhea. (SI) (8)
Parabasala
Parabasalids lack mitochondria like diplomonads. One example is the protist Trichomonas vaginalis which have flagella and an undulating
membrane.

A distinguishing characteristic of parabasala is a modified golgi apparatus know as a parabasal body, giving them their name. This organelle works closely with the basal body of the cell. (LJ)


Euglenozao
Euglenozao consists of euglenoids and kinetoplastids. Euglenoids have an anterior pocket, chamber in the front, from which one or two flagella emerge. Another characteristic of euglenoids is having paramylon, a glucose polymer that functions as a storage molecule. Kinetoplastids have kinetoplasts, organelles with extranuclear DNA.
Kinetoplastids parasitize most animals, insects, and plants. There are free-living Kinetoplastids who feed on bacteria and live in marine, aquatic and terrestrial environments. Three types of Kinetoplastids cause human disease: African typanosomes (African sleeping sickness), Trypanosoma cruzi (Chagas' disease), and Leishmania species (leishmaniasis). (MC)

Alveolata
Alveolata is made up of dinoflagellates, apicomplexans, and ciliates. Alveolates have aveoli, small membrane-bounded cavities, under the surface of the cell. Dinoflagellates tend to be single-celled organisms and each species has its own unique shape reinforced in some with internal plates of cellulose. They are also known for their spinning movement produced by the two flagella it has. Apicomplexans are parasites of animals; one example of an apicomplexan is Plasmodium, the parasite that causes malaria. At one point in their life cycle they take on the form of small infectious cells called sporozoites. At one end of these cells there is a complex of organelles that are specialized to penetrate host cells and tissues. It is the complex of organelles they are named after. Ciliates are named after their use of cilia to move about and feed. They have a submembrane system of microtubules that coordinate the movement of the thousands of cilia. They also have two different types of nuclei, a large macronucleus and smaller micronuclei.
Alveolata have mitochondria with tubular cristae. Also, some dinoflagellates, such as those in the genus Noctiluca, have the ability to bioluminesce (make their own light). (AK) (15)

Stramenopila
These protists are named after the hair-like projections on the flagella. Stramenopila is made up of oomycotes and heterokont algae. Oomycotes are water molds and their relatives. Some are unicellular; others consist of branching filaments which are multi-nucleated. These branching filaments, hyphae, are analogous to hyphae of true fungi.
Heterokont algae
These are mostly
photosynthetic, and have two different types of flagella one with "hair" and one without like the rest of the stramenopile group. This group includes diatoms, golden algae, and brown algae. Bacillariophyta or diatoms have glass like shells that have tiny pore that allow for the exchange of gases and other materials. Chrysophyta or golden algae are named for their color which is produced from accessory pigments. Most are single-cellular and some are mixotrophic. Phaeophyta or brown algae named for its brown color due to accessory pigments are all multicellular and most are marine organisms. They are made up of the largest and most complex algae.


Rhodophyta
Rhodophyta or red algae are known for their reddish color. They are also have no stage in their life cycle with flagella unlike most protists. Most are red algae are multicellular. Also these algae depend on water currents to bring gametes together.

Rhodophyta differ from many other eukaryotes because they have unstacked thylakoids in plastids. They also lack a chloroplast endoplasmic reticulum. (SI) (7)

Rhodophyta are red due to the presence of the pigment phycoerythrin (which reflects red light and absorbs blue light). Becuase blue light penetrates the water to greater depths than lights of greater wave lengths, red algae can photosynthesize and live at greater depths than other algae. In Asia, Rhodophyta is an important source of food, which began in Japan more the 300 years ago. (MLK) (17)

Chlorophyta
Also know as green algae these protists that are in fact more closely related to land plants get their name from the green chloroplasts the contain. Most green algae have both sexual and asexual stages. Chlorophyta can be unicellular, mulitcellular, or even colonial. (SM)(3)
Their colors range from green to orange. Their cell wall is similar to terrestrial plants' because it contains mostly cellulose and pectins. They are more frequently found in freshwater. Some live on snow fields or in glaciers. (SI) (6)
The photosynthetic pigments of Chlorophyta chloroplasts are also very similar to plants. (KL) (11)

(uses pseudopodium)
Rhizopoda
Also known as amoebas these single-celled organisms use pseudopodia to move about and to feed. When it moves it extends a pseudopodium, "rootlike foot"; anchors its tip; and then sends more of its cytoplasm into the pseudopodium.
Actinopoda
Actinopoda consists of heliozoans and radiolarians. They have axopodia, slender pseudopodia, that radiate from them. Heliozoans live in fresh water and their skeletons consist of unfused plates. Radiolarians are mostly marine organisms and their skeletons are fused into one piece.
Foraminifera
Foraminiferans also known as forams are mostly marine protists. Most live in sand or attached to rock and algae, but some are in plankton. They have shells with pores in them so that pseudopodia can extend through them. The pseudopodia are used for swimming, shell formation, and feeding.


Mycetozoa
Also called slime molds these are not true fungi or animals but they are decomposers. Slime molds also use pseudopodia for movement and feeding. Mycetozoa consists of Myxogastrida and Dictostelida.
Myxogastrida
These are the plasmodial slime molds all of which are heterotrophic. The feeding stage of the life cycle is a plasmodium, amoeboid mass. The plasmodium may grow to a diameter of several centimeters but it is still a single cell. Rather than the entire cell dividing only the nucleus divided so this mass has multiple nuclei. When the environment lacks sufficient moisture or food the plasmodium stops growing and changes to the next stage of the life cycle that functions in sexual reproduction.
Dictyostelida
These are the Cellular slime molds. During the feeding stage of their life cycle they are single cells and not part of a group. In the next stage of their life they look like a plasmodial slime mold except they remain an individual and separated by their membranes. These are haploid organisms and they have no stages where they have flagel
la.

Sporozoans
Sporozoans are among the four groups of protozoans, which are unicellular, heterotrophic Eukaryotes. Sporozoans have no physical form of movement. They rely on the fluids of the host, such as the currents of the blood, to move. They live inside red blood cells, where they are protected from antibodies. Members of this group, called Plasmodium vivax, cause malaria. (MT) (3).
Below is a diagram of the process by which sporozoan travel through the human blood stream. (MT)

external image malaria.jpgBASIC ANATOMY
The majority of protists are single celled organisms. All protists are eukaryotic, so they have membrane-enclosed organelles and nuclei. Most protists at some point have flagella.
(YA)(2) Because there is such a variety of organisms in the Protista kingdom, not all have the same anatomical structures that enable them to move. For example, Protists with pseudopods, such as amebas, move by extending their bodies forward and then pulling the rest of their bodies along. The finger-like structures that they project forward are called pseudopods, hence the name. They also use pseudopods to catch food. Protists with cillia, such as the paramecium, move by beating tiny hair-like structures called cilia. The cilia act as tiny oars that allows the protist to move through its watery environment, and also enables it to obtain food. Protists with flagella, such as the Giardia, move around in the bodies of other organisms, by beating their long whiplike structures called flagella. These protists can also have one or more flagella that help them move.
Euglena, a protist with flagellum to move around in water (TM)(10)
Euglena, a protist with flagellum to move around in water (TM)(10)
Protists in freshwater environment often have contractile vacuoles which pump out excess water to prevent the cell from bursting(cytolysis). Some protists have a mouth like structure called a gullet into which food is swept. Some protists like the paramecium have a membrane covering called the pellicle instead of a cell wall. A primitive light sensor is present in euglenids called an eyespot. Protists might have both a macronucleus and a micronucleus. The macronucleus controls most functions and genes except for reproduction, which the micronucleus is in charge of.(ORS 9)


TRANSPORT OF MATERIALS
Transportation of materials mostly occurs on a cellular level. A single-celled protist living in the water can take in or let out materials through their cell membrane and materials move about in the cytoplasm of the cell. Protists with pseudopodia can use them to surround and then take in their food.
Protists take in nutrients through endocytosis. The two types are phagocytosis, which is like cell eating, and pinocytosis, which is similar to cell drinking. In phagocytosis, pseudopods from the cell push through the cell membrane and surround the particle trying to be absorbed. Pinocytosis is the same process but with fluids. (NG)
A third type of endocytosis, called receptor-mediated endocytosis, involves the use of receptor sites on the protist's surface. These recognize specific ligands, and then bind to them. A ligand is a substance that binds specifically to a chemical receptor. Receptor-mediated endocytosis is much more efficient than pinocytosis, because it is specific and allows a protist to obtain large quantities of the macromolecules it needs. (ZXU)(11)(12)


REPRODUCTION
Reproduction varies amongst protists. Almost all protists undergo mitosis, the process of a cell dividing to form two daughter cells with half the normal number of chromosomes. These cells that have only half the normal number of chromosomes are said to be haploid, and a cell with a normal set of chromosomes is diploid. Most protists tend to reproduce asexually, but some others do reproduce sexually.
All three types of sexual life cycles (Chapter 13) are found among protists along with some protists that do not fit any of the three, but most protists exhibit the second type of sexual life cycle. The first type is where meiosis produces haploid gametes, which do not divide again until after fertilization. The diploid zygote then divides by mitosis. The second type is where haploid gametes fuse to form a diploid zygote, and then the zygote goes through meiosis to produce haploid cells. These haploid cells then go through mitosis to develop into a multicellular organism. In order to produce haploid gametes the organism goes through mitosis. The third type has both a diploid multicellular stage and a haploid multicellular stage. First the diploid multicellular organism goes through meiosis to produce haploid cells, or spores. These spores go through mitosis to produce a haploid multicellular organism which makes gametes through mitosis. Fertilization of these gametes results in a diploid zygote which then develops into the diploid multicellular organism.
During the life cycle of many protists they will form cysts, cells that can survive harsh conditions.
Protists undergo alternation of generations during their lifetimes.
This diagram exemplifies the unique reproductive diversity of protists in slime molds, which cycle between sexual and asexual reproduction.
This diagram exemplifies the unique reproductive diversity of protists in slime molds, which cycle between sexual and asexual reproduction.
(CW)(18)


ENVIRONMENTAL ADAPTIONS
One necessary adaption for protists is to be able to regulate the flow of water through the cell membrane as they live in very moist environments. Some protists have cell membranes that are less permeable to water than other organisms membranes. One very helpful organelle for this problem is a contractile vacuole which can spit out excess water.
Some protists, notably algal and parasitic protists, have periods of dormancy during their life cycles. They enter these periods when environmental conditions are unfavorable, such as when temperatures are too high or the food supply is low. (KS)


QUESTIONS
1. Describe the basic anatomy(structure) of protists and its locomotion. (ZS)
2. What is the purpose of the contractile vacuole in protists? (LW)
3. What type of endocytosis do protists use that functions by recognizing specific ligands? What allows the protist to sense these lingands? (SD)
4. How do protists adapt to the environment? (RG)
5. Describe the life cycle of protists. Include all the stages in its development. (DB)

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