Chapter 20 The Diversity of Protists 20 1 What Are Protists Most protists are single celled Protists include any eukaryote that is not a plant animal or fungus Most protists are microscopic in size Some are large aggregations or colonies of single celled individuals others are multicellular organisms Protists use diverse modes of nutrition They may ingest food They may absorb nutrients from their surroundings They may perform photosynthesis Protists that ingest food are typically predators Most use extensions of the cell membrane called pseudopods to surround and engulf prey Pseudopods Fig 20 1 Protists that absorb nutrients directly from the surrounding environment are of two types Free living types in the soil that decompose organic dead matter Parasites that live inside the bodies of a host organism Photosynthetic protists are abundant in oceans lakes and bonds and are collectively known as algae Single celled non photosynthetic protists are collectively known as protozoa Protists use diverse modes of reproduction Most protists reproduce asexually by mitotic cell division Some also reproduce sexually Two individuals contribute genetic material to an offspring that is genetically different from either parent Protists affect humans and other organisms The ecological role of photosynthetic marine protists algae has a positive impact They capture solar energy and make it available to the other organisms in the ecosystem They also release oxygen gas into the water As the source of many human and plant diseases protists can have a negative impact Parasitic protists cause some of humanity s most deadly diseases Protists also cause diseases in crops such as blight that destroys potatoes Some marine protists release toxins that can accumulate to harmful levels in coastal areas such as red tide 20 2 What are the major groups of Protozoans 1 Excavates have a feeding groove and lack mitochondria Groove resembles a hole or a ditch hence the name Includes Giardia which causes gastrointestinal diseases in humans 2 Euglenozoans have distinctive mitochondria Live mostly in freshwater and swim by flagella Includes Euglena which contains a photoreceptor that detects the direction of light and allows the organism to move towards light to perform photosynthesis Euglena A Representative Euglenozoan flagellum eyespot contractile vacuole stored food nucleus nucleolus chloroplasts Fig 20 5 3 Stramenopiles include photosynthetic and non photosynthetic organisms All members of the group have fine hair like projections on their flagella Can be unicellular or multicellular Include water molds the diatoms and brown algae such as kelp Brown Algae a Multicellular Protist Fig 20 9 4 Alveolates include parasites predators and phytoplankton Single celled Can cause red tide that suffocates marine life and produce a toxin that can be lethal to humans and is found in some shellfish Includes Plasmodium which causes malaria A Red Tide Fig 20 11 5 Rhizarians include the foraminiferans and the radiolarians The pseudopods are thin and thread like and may extend through elaborate shells foraminiferans produce chalky shells while radiolarians produce glassy shells made of silica Foraminiferans and Radiolarians Fig 20 15 5 Amoebozoans inhabit aquatic and terrestrial environments they feed and move by pseudopods Can be predatory or parasitic Includes a particular type of amoeba that can cause dysentery An Amoeba Fig 20 16 6 Red algae live primarily in clear tropical oceans Multicellular photosynthetic seaweeds Contain pigment that can range in color from red to black Found in deep clear waters where their red pigments absorb the deeply penetrating blue green light and transfer this light energy to chlorophyll for photosynthesis Contribute to the formation of certain reefs Red Algae Fig 20 19 7 Green algae live mostly in ponds and lakes Photosynthetic protists May be multicellular or unicellular Closely related to plants and some scientists believe that the earliest plants were similar to today s multicellular green algae
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