Lecture_Presentation_28_protists(2) (1).pptx

Chapter 28 Protists Lecture Presentations by Nicole Tunbridge and © 2021 Pearson Education, Inc. Kathleen Fitzpatrick Figure 28.1b © 2021...

Chapter 28 Protists Lecture Presentations by Nicole Tunbridge and © 2021 Pearson Education, Inc. Kathleen Fitzpatrick Figure 28.1b © 2021 Pearson Education, Inc. CONCEPT 28.1: Most eukaryotes are single- celled organisms Protist is an informal term used to refer to all eukaryotes that are not plants, animals, or fungi This group is no longer considered a kingdom because some protists are more closely related to plants, fungi, or animals than other protists © 2021 Pearson Education, Inc. Figure 28.1a  The cells of protists and other eukaryotes have a nucleus and other membrane-enclosed organelles Organelles isolate functions within eukaryotic cells, making them more complex than prokaryotic cells The well-developed cytoskeleton of the eukaryotic cell allows it to have asymmetric shape and to change shape over time Protists make up much of the diversity of eukaryotes – The organisms in most eukaryotic lineages are protists – Most protists are unicellular organisms © 2021 Pearson Education, Inc. Structural and Functional Diversity in Protists Protists exhibit more structural and functional diversity than any other group of eukaryotes Though most are unicellular, there are some colonial and multicellular protist species Unicellular protists are the most complex of all cells because each cell must carry out all functions of life Some unicellular protists have organelles not found in most other eukaryotic cells – For example, some dinoflagellate protists have an eye-like organelle called an ocelloid © 2021 Pearson Education, Inc. Figure 28.2 © 2021 Pearson Education, Inc.  Protists are the most nutritionally diverse of all eukaryotes – Some are photoautotrophs containing chloroplasts – Some are heterotrophs that absorb organic molecules or ingest larger food particles – Some are mixotrophs that combine photosynthesis and heterotrophic nutrition Some protists only reproduce asexually; others have both asexual and sexual phases in their life cycle All three basic types of sexual life cycles (animal, plant, and fungal) are represented among protists © 2021 Pearson Education, Inc. Endosymbiosis in Eukaryotic Evolution There is abundant evidence that much of protistan diversity has its origins in endosymbiosis Endosymbiosis is a relationship between two species in which one organism lives inside the cell or cells of the other organism (the host) © 2021 Pearson Education, Inc.  Mitochondria and plastids are derived from bacteria that were engulfed by ancestors of early eukaryotes Evidence suggests that mitochondria evolved before plastids and arose from an alpha proteobacterium Molecular analysis indicates that mitochondria and plastids each evolved only once in the history of life The ancestral host was a relatively complex cell with eukaryotic features, such as a cytoskeleton The host cell lineage is uncertain, but lokiarchaeotes, the archaean sister group to the eukaryotes, is a candidate taxon © 2021 Pearson Education, Inc. Plastid Evolution: A Closer Look The evolution of mitochondria gave rise to the eukaryotes Plastids arose later when a heterotrophic eukaryote engulfed a photosynthetic cyanobacterium Two lineages of photosynthetic protists, red and green algae, evolved from the plastid-bearing ancestor Figure 28.3 © 2021 Pearson Education, Inc. Four Supergroups of Eukaryotes Our understanding of the evolutionary relationships among protist groups continues to change rapidly One current hypothesis divides all eukaryotes (including protists) into four supergroups Figure 28.5 © 2021 Pearson Education, Inc. Figure 28.5 Exploring protistan diversity 1. Excavata This supergroup includes three clades: parabasalids, diplomonads, and euglenozoans – For example, Giardia intestinalis is a diplomonad parasite that causes intestinal infections in mammals Figure 28.5 © 2021 Pearson Education, Inc.  2. SAR This supergroup includes three large clades: Stramenopila, Alveolata, and Rhizaria – For example, diatoms are important photosynthetic stramenopiles – For example, many rhizarians are amoebas with threadlike pseudopodia, such as Globigerina Figure 28.5 © 2021 Pearson Education, Inc.  3. Archaeplastida This supergroup includes red and green algae, and plants Red and green algae include unicellular, colonial, and multicellular species – For example, Volvox is a multicellular green algae Video: Volvox https://www.youtube.com/watch ?v=bK5GK4BwMmE Figure 28.5 © 2021 Pearson Education, Inc.  4. Unikonta This supergroup includes amoebas with lobe- or tube-shaped pseudopodia, animals, fungi, and non- amoeba protists closely related to animals or fungi – For example, Amoeba proteus is a tubulinid amoeba Video: Amoeba Pseudopodium https://www.youtube.com/watch ?v=mv6Ehv06mXY Figure 28.5 © 2021 Pearson Education, Inc.  The root of the eukaryotic tree is not known Some major new groups of protists have been recently discovered, but their relationship to the supergroups is unresolved – For example, haptophytes, cryptophytes, and hemimastigophores are unresolved groups Figure 28.6 A haptophyte and a cryptophyte © 2021 Pearson Education, Inc. CONCEPT 28.2: Excavates include protists with modified mitochondria and protists with unique flagella 1. Excavata is characterized by its cytoskeleton Some members have an “excavated” feeding groove on one side of the body The excavates include three monophyletic groups: the diplomonads, parabasalids, and euglenozoans © 2021 Pearson Education, Inc. 1.1 & 1.2 Diplomonads and Parabasalids Diplomonads and parabasalids lack plastids and have reduced mitochondria Most live in anaerobic environments Diplomonads have reduced mitochondria, called mitosomes, that lack electron transport chains Energy is derived from anaerobic pathways They have two equal-sized nuclei and multiple flagella Many are parasites, such as Giardia intestinalis © 2021 Pearson Education, Inc.  Parabasalids have reduced mitochondria, called hydrogenosomes, that generate some energy anaerobically Hydrogen gas is released as a by-product of anaerobic metabolism The best known parabasalid is Trichomonas vaginalis, a sexually transmitted parasite It travels along the human reproductive and urinary tracts and feeds on the vaginal lining in females T. vaginalis infects about 140 million people per year worldwide Figure 28.7 The parabasalid parasite Trichomonas vaginalis © 2021 Pearson Education, Inc. 1.3 Euglenozoans Euglenozoa is a diverse clade including predatory heterotrophs, photosynthetic autotrophs, mixotrophs, and parasites The main feature distinguishing the clade is a spiral or crystalline rod inside each flagella This clade includes the kinetoplastids and euglenids Figure 28.8 Euglenozoan flagellum © 2021 Pearson Education, Inc. 1.3 (1) Kinetoplastids Kinetoplastids have a single mitochondrion containing an organized mass of DNA called a kinetoplast Free-living species are consumers of prokaryotes in freshwater, marine, and moist terrestrial ecosystems Some species parasitize animals, plants, and other protists – For example, members of the genus Trypanosoma infect humans, causing sleeping sickness in about 10,000 people per year – Trypanosomes also cause Chagas’ disease which can lead to congestive heart failure © 2021 Pearson Education, Inc.  Trypanosomes have a single cell-surface protein that changes from one generation to the next The host is prevented from developing immunity by this “bait-and-switch” defense Figure 28.9 Trypanosoma, the kinetoplastid that © 2021 Pearson Education, Inc. causes sleeping sickness 1.3 (2) Euglenids Euglenids have one or two flagella that emerge from a pocket at one end of the cell Some species are mixotrophs that switch between autotrophic and heterotrophic modes, depending on the environmental conditions Figure 28.10 Euglena, a euglenid commonly found in pond water Video: Euglena https://www.youtube.c om/watch?v=jl0TzaW UQWk © 2021 Pearson Education, Inc. CONCEPT 28.3: SAR is a highly diverse group of protists defined by DNA similarities 2. SAR is a monophyletic supergroup named for the first letters of its three major clades: stramenopiles, alveolates, and rhizarians © 2021 Pearson Education, Inc. Figure 28.UN02 In-text figure, the SAR clade 2. 1 Stramenopiles Stramenopiles include some of the most important photosynthetic organisms on Earth Most have a “hairy” flagellum paired with a “smooth” flagellum Diatoms, oomycetes, and brown algae are three important groups of stramenopiles Figure 28.11 Stramenopile flagella © 2021 Pearson Education, Inc. 2.1 (1) Diatoms Diatoms are unicellular algae with a unique two- part, glass-like wall of silicon dioxide The wall withstands pressure up to 1.4 million kg/m2, protecting diatoms from the crushing jaws of predators Video: Various Diatoms https://www.youtube.com/watch ?v=vzRkHkssdME Figure 28.12 The diatom Triceratium morlandii © 2021 Pearson Education, Inc.  Including about 100,000 species, diatoms compose much of the phytoplankton in the ocean and lakes Diatoms are so abundant and widespread that their photosynthetic activity affects global CO2 levels After a diatom bloom, many dead individuals fall to the ocean floor, where decomposition is slow The breakdown and release of carbon stored in the diatoms on the ocean floor can take centuries Promoting diatom blooms by fertilizing the ocean with essential nutrients is a proposed approach to reduce atmospheric CO2 levels © 2021 Pearson Education, Inc. 2.1 (2) Brown Algae Brown algae are the largest and most complex multicellular algae Carotenoids in the plastids produce the brown color Most are marine, including many species commonly called “seaweeds” Brown algae are important commodities for humans – For example, some species, such as Laminaria are eaten – Algin, a gel-forming substance found in the cell wall, is used as a thickener in many processed foods © 2021 Pearson Education, Inc. Figure 28.13 Brown algal seaweeds have plantlike structures: the rootlike holdfast, which anchors the alga, and a stemlike stipe, which supports the leaflike blades Some have gas-filled, bubble- shaped floats to keep photosynthetic structures near the water surface Brown algae lack the true tissues and organs found in plants © 2021 Pearson Education, Inc. Alternation of Generations A variety of life cycles have evolved among the multicellular algae Some have alternation of generations, in which both haploid and diploid stages are multicellular The diploid generation is called a sporophyte because it produces spores Haploid spores develop into multicellular haploid gametophytes that produce haploid gametes Fertilization of gametes results in a diploid zygote, which develops into a new sporophyte © 2021 Pearson Education, Inc. Figure 28.14 © 2021 Pearson Education, Inc. 2.1 (3) Oomycetes (Water Molds and Their Relatives) Oomycetes include water molds, white rusts, and downy mildews They were misidentified as fungi due to their multinucleate filaments that resemble fungal hyphae One key difference is that oomycetes cell walls are composed of cellulose, rather than chitin Based on molecular analysis, oomycetes and fungi are not closely related © 2021 Pearson Education, Inc.  Oomycetes are related to plastid-bearing groups, but do not have plastids or perform photosynthesis They acquire nutrients through parasitism or decomposition – For example, Phytophthora infestans is a parasite that causes potato late blight, a disease that kills potato crops Figure 28.15 Oomycetes © 2021 Pearson Education, Inc. 2.2 Alveolates Alveolates have membrane-enclosed sacs (alveoli) just under the plasma membrane Three clades included in the alveolates are the dinoflagellates, the apicomlexans, and the ciliates Figure 28.16 Alveoli © 2021 Pearson Education, Inc. 2.2 (1) Dinoflagellates Dinoflagellates are abundant components of marine and freshwater phytoplankton They have two flagella housed in the grooves of armor-like cellulose plates that surround the cell Beating of the spiral flagella causes dinoflagellates to spin as they move through the water Video: Dinoflagellate Figure 28.17 Dinoflagellates https://www.youtube.com/watch?v =6iM63hIUiuU © 2021 Pearson Education, Inc.  Dinoflagellate blooms cause “red tides” where the water appears brownish red or pink due to the carotenoids present in their plastids Red tides are toxic and can cause massive kills of invertebrates and fishes Ocean warming caused by climate change is facilitating more frequent red tides Figure 28.17 Dinoflagellates © 2021 Pearson Education, Inc. 2.2 (2) Apicomplexans Nearly all apicomplexans are parasites of animals They spread through the host as infectious cells called sporozoites The apex (cell end) contains a complex of organelles specialized for penetrating host cells and tissues Most life cycles include both sexual and asexual stages, and require two or more different hosts – For example, Plasmodium, the parasite causing malaria, lives in both mosquitoes and humans © 2021 Pearson Education, Inc. Figure 28.18 © 2021 Pearson Education, Inc.  Plasmodium evades the host immune system by living inside cells and continually changing its surface proteins Approximately 220 million people in the tropics are infected and 450,000 die each year from malaria The first licensed malarial vaccine was recently approved and routine use began in Africa in 2019 The vaccine, which targets a protein on the surface of sporozoites, provides only partial protection Research into other potential vaccine targets is ongoing © 2021 Pearson Education, Inc. 2.2 (3) Ciliates Ciliates are named for their use of cilia to move around and feed on bacteria or other protists The cilia may completely cover the cell surface or be clustered in a few rows or tufts Figure 28.19 Structure and function in the ciliate Paramecium caudatum Video: Paramecium Cilia https://www.youtube.com/watch?v=RyQfvxH425Q © 2021 Pearson Education, Inc.  Ciliates have two types of nuclei: tiny micronuclei and large macronuclei Each cell has one or more copies of each type Macronuclei have multiple copies of the genome Micronuclei may be diploid or haploid, depending on the life stage Conjugation produces genetic variation without reproduction through the exchange of micronuclei Asexual reproduction occurs by binary fission During binary fission, the macronucleus dissolves and a new one is formed from micronuclei © 2021 Pearson Education, Inc. Figure 28.19 © 2021 Pearson Education, Inc. 2.3 Rhizarians Many species of rhizarians are amoebas Amoebas are protists that move and feed using pseudopodia, extensions of the cell surface Rhizarian amoebas differ from amoebas in other clades by having threadlike pseudopodia Three clades included in the rhizarians are radiolarians, forams, and cercozoans © 2021 Pearson Education, Inc. 2.3 (1) Radiolarians Radiolarians have delicate, symmetrical internal skeletons typically made of silica Pseudopodia reinforced by microtubules radiate from the central body Prey are engulfed by cytoplasm in the pseudopodia and carried into the cell by cytoplasmic streaming Most radiolarians are marine organisms Figure 28.20 A radiolarian © 2021 Pearson Education, Inc. 2.3 (2) Forams Foraminiferans, or forams, are named for their porous calcium carbonate shells, called tests Pseudopodia that extend through pores in the test are used in swimming, test formation, and feeding Some host mutualistic photosynthetic algae within their tests Forams live in the ocean and fresh water, and their fossils make up part of the marine sediments Fossilized tests are used for correlating the age of sedimentary rocks in different parts of the world The magnesium content of fossilized tests is used to estimate the change in ocean temperature over time © 2021 Pearson Education, Inc. Figure 28.21 © 2021 Pearson Education, Inc. 2.3 (3) Cercozoans Cercozoans are amoeboid and flagellated protists that feed using threadlike pseudopodia They are common in marine, fresh water, and soil ecosystems Most cercozoans are heterotrophic parasites or predators Chlorarachniophytes are a small group of mixotrophs At least one species, Paulinella chromatophora, is known to be autotrophic © 2021 Pearson Education, Inc. CONCEPT 28.4: Red algae and green algae are the closest relatives of plants Plastids arose when a heterotrophic protist acquired a cyanobacterial endosymbiont The photosynthetic descendants of this ancient protist evolved into red algae and green algae Plants are descended from the green algae 3. Archaeplastida is the supergroup that includes red algae, green algae, and plants © 2021 Pearson Education, Inc. 3.1 Red Algae An accessory pigment called phycoerythrin masks the green of chlorophyll giving red algae its color Color varies from greenish-red in shallow water to dark red or almost black in deep water Most are multicellular; the largest are seaweeds Reproduction is sexual in red algae and life cycles often include alternation of generations Red algae are common in coastal waters of tropical oceans Some species are consumed by humans, such as Porphyra (“nori”) that is used to wrap sushi © 2021 Pearson Education, Inc. Figure 28.23 © 2021 Pearson Education, Inc. 3.2 Green Algae Green algae are named for their green chloroplasts, which are structurally and chemically similar to those found in plants Green algae form a paraphyletic group that includes the charophytes and the chlorophytes Charophytes include the algae most closely related to plants Most chlorophytes live in fresh water, although there are many marine and some terrestrial species Various unicellular species are free-living while others live symbiotically with other eukaryotes Some live in environments exposed to intense visible and ultraviolet radiation © 2021 Pearson Education, Inc.  Larger size and greater complexity evolved in green algae by three different mechanisms: 1. Formation of colonies from individual cells (Pediastrum) 2. Formation of true multicellular bodies by cell division and differentiation (Volvox and Ulva) 3. Repeated division of nuclei with no cytoplasmic division Figure 28.24 Examples of large chlorophytes (Caulerpa) © 2021 Pearson Education, Inc.  Most chlorophytes have complex life cycles with both sexual and asexual reproductive stages Nearly all species have biflagellated gametes with cup- shaped chloroplasts Alternation of generations has evolved in some chlorophytes, including Ulva © 2021 Pearson Education, Inc. Figure 28.25 The life cycle of Chlamydomonas, a unicellular chlorophyte Animation: Alternation of Generations in a Protist https://www.youtube.com/watch?v=8PHo-4obHj w © 2021 Pearson Education, Inc. CONCEPT 28.5: Unikonts include protists that are closely related to fungi and animals The supergroup 4. Unikonta includes animals, fungi, and some protists The two major clades of unikonts are the amoebozoans (tubulinids and relatives) and the opisthokonts (animals, fungi, and related protists) Figure 28.UN04 In-text figure, Unikonta © 2021 Pearson Education, Inc.  The root of the eukaryotic tree is uncertain One controversial hypothesis is that unikonts were the first to diverge from other eukaryote groups Figure 28.26 Inquiry: What is the root of the eukaryotic tree? © 2021 Pearson Education, Inc. Amoebozoans Amoebozoans are amoebas that have lobe- or tube-shaped, rather than threadlike, pseudopodia They include tubulinids, slime molds, and entamoebas © 2021 Pearson Education, Inc. Tubulinids Tubulinids are a diverse group of amoebozoans with lobe- or tube-shaped pseudopodia They are common unicellular protists in soil as well as freshwater and marine environments Most tubulinids are active predators of bacteria and other protists; others feed on detritus © 2021 Pearson Education, Inc. Slime Molds Slime molds, or mycetozoans, were once thought to be fungi due to their spore-producing fruiting bodies This resemblance is a result of convergent evolution Slime molds have diverged into two lineages, plasmodial slime molds and cellular slime molds © 2021 Pearson Education, Inc. Plasmodial Slime Molds Many plasmodial slime molds are brightly colored, often yellow or orange They form a large feeding mass called a plasmodium The plasmodium is a single “supercell” that contains many diploid nuclei undivided by plasma membranes The plasmodium forms a fruiting body for sexual reproduction in unfavorable environmental conditions © 2021 Pearson Education, Inc.  Cellular Slime Molds Cellular slime molds form multicellular aggregates in which cells are separated by plasma membranes The feeding stage consists of solitary cells Solitary cells unite to form a slug-like aggregate for migration when habitat conditions are poor Ultimately, the aggregated cells form a fruiting body Figure 28.28 The life cycle of Dictyostelium, a cellular slime mold © 2021 Pearson Education, Inc.  Cellular Slime Molds Dictyostelium discoideum is a model organism for the studying the evolution of multicellularity Cells in the stalk of the fruiting body die without reproducing; cells at the top survive to reproduce Some cells have a “cheat” mutation, giving them the reproductive advantage of not forming the stalk Why don’t all Dictyostelium cells cheat? Cheating cells lack a specific surface protein recognized by noncheaters Non-cheaters avoid exploitation by preferentially aggregating with other noncheaters Such a recognition system may have been important in the evolution of other multicellular eukaryotes Smart slime mold https://www.youtube.com/watch?v=K8HEDqoTPgk © 2021 Pearson Education, Inc. Entamoebas Members of the genus Entamoeba are parasites of all classes of vertebrates and some invertebrates Humans are host to at least six species, but only E. histolytica is pathogenic E. histolytica causes amoebic dysentery, the third- leading cause of death due to eukaryotic parasites Opisthokonts Opisthokonts are a diverse group including animals, fungi, and several groups of protists © 2021 Pearson Education, Inc. CONCEPT 28.6: Protists play key roles in ecological communities Protists are found in diverse aquatic and moist terrestrial environments Protists play two key roles in their habitats: that of symbiont and that of producer © 2021 Pearson Education, Inc. Symbiotic Protists Some protist symbionts benefit their hosts – Some dinoflagellates live within the polyps and nourish reef-building corals – Some protists inhabit the guts of termites and aid with the digestion of wood Figure 28.29 A symbiotic protist © 2021 Pearson Education, Inc.  Some protist symbionts are parasites – Plasmodium causes malaria in humans – Pfiesteria shumwayae is a dinoflagellate that attaches and feeds on the skin of fish – Phytophthora ramorum causes sudden oak death © 2021 Pearson Education, Inc. Figure 28.30 Sudden oak death Photosynthetic Protists Many protists are producers, organisms that use energy from light (or inorganic compounds) to convert CO2 to organic compounds In aquatic communities, the main producers are photosynthetic protists and prokaryotes All other organisms are consumers that directly or indirectly depend on producers for food Figure 28.31 Protists: key producers in aquatic communities © 2021 Pearson Education, Inc.  Photosynthetic protists are limited by nutrients; populations explode when nutrients are added Population booms can have major ecological consequences, such as the formation of marine “dead zones” Growth and biomass of photosynthetic protists and prokaryotes have declined with increasing sea surface temperature Phytoplankton communities rely on upwelling of cold, nutrient-rich water from the below Warm surface water acts as a barrier to upwelling © 2021 Pearson Education, Inc.  If sea surface temperature continues to warm due to global warming, this could have large effects on – marine ecosystems – fishery yields – the global carbon cycle Figure 28.32 Effects of climate change on marine producers © 2021 Pearson Education, Inc. Figure 28.UN06 © 2021 Pearson Education, Inc.