{"id":1337,"date":"2017-01-18T22:54:54","date_gmt":"2017-01-18T22:54:54","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/wm-biology2\/?post_type=chapter&p=1337"},"modified":"2017-07-05T16:55:57","modified_gmt":"2017-07-05T16:55:57","slug":"characteristics-of-protists","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-wmopen-biology2\/chapter\/characteristics-of-protists\/","title":{"raw":"Characteristics of Protists","rendered":"Characteristics of Protists"},"content":{"raw":"

Identify the common characteristics of protists<\/h2>\r\nThere are over 100,000 described living species of protists, and it is unclear how many undescribed species may exist. Since many protists live as commensals or parasites in other organisms and these relationships are often species-specific, there is a huge potential for protist diversity that matches the diversity of hosts. As the catchall term for eukaryotic organisms that are not animal, plant, or fungi, it is not surprising that very few characteristics are common to all protists.\r\n
\r\n

Learning Objectives<\/h3>\r\n
    \r\n \t
  • Describe the cell structure of protists<\/li>\r\n \t
  • Describe the motility of protists<\/li>\r\n \t
  • Describe the metabolic diversity of protists<\/li>\r\n \t
  • Describe the life cycle and habitat diversity of protists<\/li>\r\n<\/ul>\r\n<\/div>\r\n

    Cell Structure<\/h2>\r\nThe cells of protists are among the most elaborate of all cells. Most protists are microscopic and unicellular, but some true multicellular forms exist. A few protists live as colonies that behave in some ways as a group of free-living cells and in other ways as a multicellular organism. Still other protists are composed of enormous, multinucleate, single cells that look like amorphous blobs of slime, or in other cases, like ferns. In fact, many protist cells are multinucleated; in some species, the nuclei are different sizes and have distinct roles in protist cell function.\r\n\r\nSingle protist cells range in size from less than a micrometer to three meters in length to hectares (a single hectare is nearly 2.5 acres in size). Protist cells may be enveloped by animal-like cell membranes or plant-like cell walls. Others are encased in glassy silica-based shells or wound with pellicles of interlocking protein strips. The pellicle functions like a flexible coat of armor, preventing the protist from being torn or pierced without compromising its range of motion.\r\n

    Motility<\/h2>\r\nThe majority of protists are motile, but different types of protists have evolved varied modes of movement (Figure\u00a01). Some protists have one or more flagella, which they rotate or whip: these are typically euglena<\/strong>. Others are covered in rows or tufts of tiny cilia that they coordinately beat to swim\u2014typically paramecium<\/strong>. Still others form cytoplasmic extensions called pseudopodia anywhere on the cell, anchor the pseudopodia to a substrate, and pull themselves forward in an \"oozing\" movement: these are typically amoeba<\/b>.\r\n
    <\/figure>\r\n[caption id=\"attachment_1342\" align=\"aligncenter\" width=\"800\"]\"Part Figure\u00a01. Protists use various methods for transportation. (a)\u00a0Paramecium<\/em> waves hair-like appendages called cilia to propel itself. (b)\u00a0Amoeba<\/em> uses lobe-like pseudopodia to anchor itself to a solid surface and pull itself forward. (c)\u00a0Euglena<\/em> uses a whip-like tail called a flagellum to propel itself.[\/caption]\r\n\r\nSome protists can move toward or away from a stimulus, a movement referred to as taxis. Movement toward light, termed phototaxis, is accomplished by coupling their locomotion strategy with a light-sensing organ.\r\n
    \r\n

    Practice Questions<\/h3>\r\nProtists that have a pellicle are surrounded by ______________.\r\n
      \r\n \t
    1. silica dioxide<\/li>\r\n \t
    2. calcium carbonate<\/li>\r\n \t
    3. carbohydrates<\/li>\r\n \t
    4. proteins<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"368573\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"368573\"]Answer d. Protists that have a pellicle are surrounded by proteins<\/strong>.\r\n\r\n[\/hidden-answer]\r\n\r\nWhich of these locomotor organs would likely be the shortest?\r\n
        \r\n \t
      1. a flagellum<\/li>\r\n \t
      2. a cilium<\/li>\r\n \t
      3. an extended pseudopod<\/li>\r\n \t
      4. a pellicle<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"166771\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"166771\"]Answer b. A\u00a0cilium<\/strong> would likely be the shortest locomotor organs.[\/hidden-answer]\r\n\r\n<\/div>\r\n

        Metabolism<\/h2>\r\nProtists exhibit many forms of nutrition and may be aerobic or anaerobic. Protists that store energy by photosynthesis\u00a0belong to a group of photoautotrophs and are characterized by the presence of chloroplasts. Other protists are heterotrophic and consume organic materials (such as other organisms) to obtain nutrition. Amoebas and some other heterotrophic protist species ingest particles by a process called phagocytosis, in which the cell membrane engulfs a food particle and brings it inward, pinching off an intracellular membranous sac, or vesicle, called a food vacuole (Figure\u00a02). The vesicle containing the ingested particle, the phagosome, then fuses with a lysosome containing hydrolytic enzymes to produce a phagolysosome<\/b>, and the food particle is broken down into small molecules that can diffuse into the cytoplasm and be used in cellular metabolism. Undigested remains ultimately are expelled from the cell via exocytosis.\r\n\r\n[caption id=\"attachment_1341\" align=\"aligncenter\" width=\"544\"]\"In Figure\u00a02. The stages of phagocytosis include the engulfment of a food particle, the digestion of the particle using hydrolytic enzymes contained within a lysosome, and the expulsion of undigested materials from the cell.[\/caption]\r\n\r\nSubtypes of heterotrophs, called saprobes, absorb nutrients from dead organisms or their organic wastes. Some protists, like, euglena, can function as mixotrophs<\/b>, obtaining nutrition by photoautotrophic or heterotrophic routes, depending on whether sunlight or organic nutrients are available.\r\n

        Life Cycles<\/h2>\r\nProtists reproduce by a variety of mechanisms. Most undergo some form of asexual reproduction, such as binary fission, to produce two daughter cells. In protists, binary fission can be divided into transverse or longitudinal, depending on the axis of orientation; sometimes Paramecium<\/em> exhibits this method. Some protists such as the true slime molds exhibit multiple fission and simultaneously divide into many daughter cells. Others produce tiny buds that go on to divide and grow to the size of the parental protist. Sexual reproduction, involving meiosis and fertilization, is common among protists, and many protist species can switch from asexual to sexual reproduction when necessary. Sexual reproduction is often associated with periods when nutrients are depleted or environmental changes occur. Sexual reproduction may allow the protist to recombine genes and produce new variations of progeny that may be better suited to surviving in the new environment. However, sexual reproduction is often associated with resistant cysts that are a protective, resting stage. Depending on their habitat, the cysts may be particularly resistant to temperature extremes, desiccation, or low pH. This strategy also allows certain protists to \u201cwait out\u201d stressors until their environment becomes more favorable for survival or until they are carried (such as by wind, water, or transport on a larger organism) to a different environment, because cysts exhibit virtually no cellular metabolism.\r\n\r\nProtist life cycles range from simple to extremely elaborate. Certain parasitic protists have complicated life cycles and must infect different host species at different developmental stages to complete their life cycle. Some protists are unicellular in the haploid form and multicellular in the diploid form, a strategy employed by animals. Other protists have multicellular stages in both haploid and diploid forms, a strategy called alternation of generations that is also used by plants.\r\n

        Habitats<\/h2>\r\nNearly all protists exist in some type of aquatic environment, including freshwater and marine environments, damp soil, and even snow. Several protist species are parasites that infect animals or plants. A few protist species live on dead organisms or their wastes, and contribute to their decay.\r\n
        \r\n

        Practice Questions<\/h3>\r\nExplain in your own words why sexual reproduction can be useful if a protist\u2019s environment changes.\r\n\r\n[practice-area rows=\"2\"][\/practice-area]\r\n[reveal-answer q=\"347707\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"347707\"]The ability to perform sexual reproduction allows protists to recombine their genes and produce new variations of progeny that may be better suited to the new environment. In contrast, asexual reproduction generates progeny that are clones of the parent.\r\n\r\n[\/hidden-answer]\r\n\r\nGiardia lamblia<\/em> is a cyst-forming protist parasite that causes diarrhea if ingested. Given this information, against what type(s) of environments might G. lamblia<\/em> cysts be particularly resistant?\r\n\r\n[practice-area rows=\"2\"][\/practice-area]\r\n[reveal-answer q=\"155458\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"155458\"]As an intestinal parasite, Giardia<\/em> cysts would be exposed to low pH in the stomach acids of its host. To survive this environment and reach the intestine, the cysts would have to be resistant to acidic conditions.[\/hidden-answer]\r\n\r\n<\/div>\r\n

        Check Your Understanding<\/strong><\/h2>\r\nAnswer the question(s) below to see how well you understand the topics covered in the previous section. This short quiz does\u00a0not<\/strong>\u00a0count toward your grade in the class, and you can retake it an unlimited number of times.\r\n\r\nUse this quiz to check your understanding and decide whether to (1) study the previous section further or (2) move on to the next section.\r\n\r\nhttps:\/\/assessments.lumenlearning.com\/assessments\/4941","rendered":"

        Identify the common characteristics of protists<\/h2>\n

        There are over 100,000 described living species of protists, and it is unclear how many undescribed species may exist. Since many protists live as commensals or parasites in other organisms and these relationships are often species-specific, there is a huge potential for protist diversity that matches the diversity of hosts. As the catchall term for eukaryotic organisms that are not animal, plant, or fungi, it is not surprising that very few characteristics are common to all protists.<\/p>\n

        \n

        Learning Objectives<\/h3>\n
          \n
        • Describe the cell structure of protists<\/li>\n
        • Describe the motility of protists<\/li>\n
        • Describe the metabolic diversity of protists<\/li>\n
        • Describe the life cycle and habitat diversity of protists<\/li>\n<\/ul>\n<\/div>\n

          Cell Structure<\/h2>\n

          The cells of protists are among the most elaborate of all cells. Most protists are microscopic and unicellular, but some true multicellular forms exist. A few protists live as colonies that behave in some ways as a group of free-living cells and in other ways as a multicellular organism. Still other protists are composed of enormous, multinucleate, single cells that look like amorphous blobs of slime, or in other cases, like ferns. In fact, many protist cells are multinucleated; in some species, the nuclei are different sizes and have distinct roles in protist cell function.<\/p>\n

          Single protist cells range in size from less than a micrometer to three meters in length to hectares (a single hectare is nearly 2.5 acres in size). Protist cells may be enveloped by animal-like cell membranes or plant-like cell walls. Others are encased in glassy silica-based shells or wound with pellicles of interlocking protein strips. The pellicle functions like a flexible coat of armor, preventing the protist from being torn or pierced without compromising its range of motion.<\/p>\n

          Motility<\/h2>\n

          The majority of protists are motile, but different types of protists have evolved varied modes of movement (Figure\u00a01). Some protists have one or more flagella, which they rotate or whip: these are typically euglena<\/strong>. Others are covered in rows or tufts of tiny cilia that they coordinately beat to swim\u2014typically paramecium<\/strong>. Still others form cytoplasmic extensions called pseudopodia anywhere on the cell, anchor the pseudopodia to a substrate, and pull themselves forward in an “oozing” movement: these are typically amoeba<\/b>.<\/p>\n

          <\/figure>\n
          \"Part<\/p>\n

          Figure\u00a01. Protists use various methods for transportation. (a)\u00a0Paramecium<\/em> waves hair-like appendages called cilia to propel itself. (b)\u00a0Amoeba<\/em> uses lobe-like pseudopodia to anchor itself to a solid surface and pull itself forward. (c)\u00a0Euglena<\/em> uses a whip-like tail called a flagellum to propel itself.<\/p>\n<\/div>\n

          Some protists can move toward or away from a stimulus, a movement referred to as taxis. Movement toward light, termed phototaxis, is accomplished by coupling their locomotion strategy with a light-sensing organ.<\/p>\n

          \n

          Practice Questions<\/h3>\n

          Protists that have a pellicle are surrounded by ______________.<\/p>\n

            \n
          1. silica dioxide<\/li>\n
          2. calcium carbonate<\/li>\n
          3. carbohydrates<\/li>\n
          4. proteins<\/li>\n<\/ol>\n
            Show Answer<\/span><\/p>\n
            Answer d. Protists that have a pellicle are surrounded by proteins<\/strong>.<\/p>\n<\/div>\n<\/div>\n

            Which of these locomotor organs would likely be the shortest?<\/p>\n

              \n
            1. a flagellum<\/li>\n
            2. a cilium<\/li>\n
            3. an extended pseudopod<\/li>\n
            4. a pellicle<\/li>\n<\/ol>\n
              Show Answer<\/span><\/p>\n
              Answer b. A\u00a0cilium<\/strong> would likely be the shortest locomotor organs.<\/div>\n<\/div>\n<\/div>\n

              Metabolism<\/h2>\n

              Protists exhibit many forms of nutrition and may be aerobic or anaerobic. Protists that store energy by photosynthesis\u00a0belong to a group of photoautotrophs and are characterized by the presence of chloroplasts. Other protists are heterotrophic and consume organic materials (such as other organisms) to obtain nutrition. Amoebas and some other heterotrophic protist species ingest particles by a process called phagocytosis, in which the cell membrane engulfs a food particle and brings it inward, pinching off an intracellular membranous sac, or vesicle, called a food vacuole (Figure\u00a02). The vesicle containing the ingested particle, the phagosome, then fuses with a lysosome containing hydrolytic enzymes to produce a phagolysosome<\/b>, and the food particle is broken down into small molecules that can diffuse into the cytoplasm and be used in cellular metabolism. Undigested remains ultimately are expelled from the cell via exocytosis.<\/p>\n

              \"In<\/p>\n

              Figure\u00a02. The stages of phagocytosis include the engulfment of a food particle, the digestion of the particle using hydrolytic enzymes contained within a lysosome, and the expulsion of undigested materials from the cell.<\/p>\n<\/div>\n

              Subtypes of heterotrophs, called saprobes, absorb nutrients from dead organisms or their organic wastes. Some protists, like, euglena, can function as mixotrophs<\/b>, obtaining nutrition by photoautotrophic or heterotrophic routes, depending on whether sunlight or organic nutrients are available.<\/p>\n

              Life Cycles<\/h2>\n

              Protists reproduce by a variety of mechanisms. Most undergo some form of asexual reproduction, such as binary fission, to produce two daughter cells. In protists, binary fission can be divided into transverse or longitudinal, depending on the axis of orientation; sometimes Paramecium<\/em> exhibits this method. Some protists such as the true slime molds exhibit multiple fission and simultaneously divide into many daughter cells. Others produce tiny buds that go on to divide and grow to the size of the parental protist. Sexual reproduction, involving meiosis and fertilization, is common among protists, and many protist species can switch from asexual to sexual reproduction when necessary. Sexual reproduction is often associated with periods when nutrients are depleted or environmental changes occur. Sexual reproduction may allow the protist to recombine genes and produce new variations of progeny that may be better suited to surviving in the new environment. However, sexual reproduction is often associated with resistant cysts that are a protective, resting stage. Depending on their habitat, the cysts may be particularly resistant to temperature extremes, desiccation, or low pH. This strategy also allows certain protists to \u201cwait out\u201d stressors until their environment becomes more favorable for survival or until they are carried (such as by wind, water, or transport on a larger organism) to a different environment, because cysts exhibit virtually no cellular metabolism.<\/p>\n

              Protist life cycles range from simple to extremely elaborate. Certain parasitic protists have complicated life cycles and must infect different host species at different developmental stages to complete their life cycle. Some protists are unicellular in the haploid form and multicellular in the diploid form, a strategy employed by animals. Other protists have multicellular stages in both haploid and diploid forms, a strategy called alternation of generations that is also used by plants.<\/p>\n

              Habitats<\/h2>\n

              Nearly all protists exist in some type of aquatic environment, including freshwater and marine environments, damp soil, and even snow. Several protist species are parasites that infect animals or plants. A few protist species live on dead organisms or their wastes, and contribute to their decay.<\/p>\n

              \n

              Practice Questions<\/h3>\n

              Explain in your own words why sexual reproduction can be useful if a protist\u2019s environment changes.<\/p>\n