Biology II Chapter 28

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Biology II Chapter 28
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Biology Protists Campbell
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Chapter 28 of Campbell's Biology Textbook - Protists
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  1. What is a protist?
    An informal term applied to any eukaryote that is not a plant, animal or fungus. Most protists are unicellular, though some are colonial or multicellular.
  2. (T/F) Some protists are more closely related to plants, fungi, or animals than they are to other protists. As a result, the kingdom Protista has been abandoned.
  3. (T/F) Most biologists still use the term protist, but only as a convenient way to refer to eukaryotes that are neither plants, animals, nor fungi.
    True.
  4. (T/F) Protists, along with plants, animals and fungi are classified as eukaryotes in the domain Eukarya.
    True.

    Unlike the cells of prokaryotes, eukaryotic cells have a nucleus and other membeane-bounded organelles, such as mitochondria and the Golgi apparatus.
  5. (T/F) The organisms in most eukaryotic lineages are protists, and most protists are unicellular. The large, multicellular organisms that we know best (plants, animals and fungi) are the tips of just a few branches on the great tree of life.
    True.
  6. (T/F) Protists exhibit more structural and functional diversity than any other group of eukaryotes.
    True.

    This is despite the fact that most protists are unicellular. Single celled protists are justifiably considered the simplest eukaryotes, but at the cellular level, many protists are very complex.
  7. (T/F) Unicellar protists are lacking many of the essential functions that eukaryotes have.
    False.

    Unicellular protists carry out the same essential functions, but they do so using subcellular organelles, not multicellular organs.
  8. (T/F) Unicellular protists carry out the same essential functions as the larger eukaryotes such as plants, animals and fungi, but they do so using subcellular organelles, not multicellular organs.
    True.
  9. (T/F) Certain protists rely on organelles not found in most other eukaryotic cells, such as contractile vacuoles that pump excess water from the protistan cell.
    True.
  10. What are mixotrophs? What type of organisms tend to exhibit this?
    An organism that is capable of both photosynthesis and heterotrophy.

    Some protists exhibit this characteristic.
  11. What is a nucleomorph?
    Chlorarachniophytes likely evolved when a heterotrophic eukaryote engulfed a green alga, which still carried out photosynthesis with its plastids and contains a tiny vestigial nucleus of its own.

    Consistent with the hypothesis that chlorarachinophytes evolved from a eukaryote that engulfed another eukaryote, their plastids are surrounded by four membranes. The two inner membranes originated as the inner and outer membranes of the ancient cyanobacterium. The third membrane is derived from the engulfed alga's plasma membrane, and the outermost membrane is derived from the heterotyophic eukaryote's food vacuole. In other protists, plastids acquired by secondary endosymbiosis are surrounded by three membranes, indicating that one of the original four membranes was lost during the course of evolution.
  12. What is secondary endosymbiosis?
    A process in eukaryotic evolution in which a heterotrophic eukaryotic cell engulfed a photosynthetic eukaryotic cell, which survived in a symbiotic relationship inside the heterotrophic cell.
  13. What are amitochondriate protists? What is important about these?
    A group lacking conventional mitochondria and having fewer membrane bounded organelles than other protists.

    Many of the "amitochondriate protists" do infact have mitochondria - though reduced onces.
  14. (T/F) All of the five supergroups of eukaryotes derive from the same common ancestor.
    False.

    Because the root of the eukaryotic tree is not known, all five supergroups are shown as diverging simultaneously from a common ancestor - something that is not correct but it is unknown which organisms were first diverge from the others.
  15. Studies of plastid-beating eukaryotes suggest that all plastids evolved from a gram-negative cyanobacterium that was engulfed by an ancestral heterotrophic eukaryote (primary endosymbiosis). That ancestor then diversified into ____ algae and ____ algae, some of which were engulfed by other eukaryotes (________ endosymbiosis).
    • Red, Green, secondary endosymbiosis
  16. Cite at least four examples of structural and functional diversity among protists.
    Protists include unicellular, colonial, and multicellular organisms, photoautotrophs, heterotrophs, and mixotrophs; and species that reproduce asexually, sexually, or both ways.
  17. Summarize the role of endosymbiosis in eukaryotic evolution.
    Strong evidence shows that eukaryotes acquired mitochondria after an early eukaryote first engulfed and then formed an endosymbiotic association with an alpha proteobacterium. Similarly, chloroplasts in red and green algae appear to have descended from a photosynthetic cyanobacterium that was engulfed by an ancient heterotrophic eukaryote. Secondary endosymbiosis also played an important role: Various protist lineages acquired plastids by engulfing unicellular red or green algae.
  18. What is a plastid?
    One of a family of closely related organelle that includes chloroplasts, chromosplasts, and amyloplasts (leucoplasts). Plastids are found in photosynthetic organisms.
  19. What are the five "supergroups" for the eukaryote domain? What are the supergroups that animals, plants and fungi are classified in?
    • Excavata
    • Chromalveolata
    • Rhizaria
    • Archaeplastid
    • Unikonta

    Land plants are within the Archaeplastida supergroup.

    Fungi and Animals are within the Unikonta supergroup.
  20. What are included in the supergroup Excavata?
    Excavates include parasites such as Giardia, as well as many predatory and photosynthetic species.

    • Some members of this supergroup have an excavated groove on one side of the cell body. Two major clades (the parabasalids and diplomanads) have modified mitochondria; others (the euglenozoans) have flagella that differ in structure from those of other organisms.
  21. What are included in the supergroup Chromalveolata?
    CChromalveolates include some of the most important photosynthetic organisms on Earth. This group includes the brown algae that form underwater kelp "forests" as well as important pathogens such Plasmodium, which causes malaria, and Phytophthora, which caused the devastating potato famine in 19th century Ireland.

    • This group may originated by an ancient secondary endosymbiosis event.
  22. What are included in the supergroup Rhizaria?
    This group consists of species of amoebas, most of which have pseudopodia that are threadlike in shape.

    • Pseudopodia are extensions that can bulge from any portion of the cell; they are used in movement an in the capture of prey.
  23. What are included in the supergroup Archaeplastida?
    This group of eukaryotes includes red algae and green algae, along with land plants. Red algae and green algae include unicellular species, colonial species (such as the green alga Volvox), and multicellular species. Many of the large algae known informally as "seaweeds" are multicellular red or green algae. Protists in Archaeplastida include key photosynthetic species that form the base of the food web in some aquatic communities.

  24. (T/F) Green algae, red algae, brown algae, and golden algae are all included in the same supergroup.
    False.

    Green and red algae are included in the supergroup Archaeplastida.

    Golden and brown algae are included in the supergroup Chromalveolata.
  25. (T/F) Land plants are included in the Archaeplastida supergroup with green and red algae.
    True.
  26. (T/F) Fungi and animals are in the same supergroup with Unikonta.
    True.
  27. What are included in the supergroup Unikonta?
    This group of eukaryotes includes amoebas that have lobe- or tube-shapped pseudopodia, as well as animals, fungi, and protists that are closely related to animals or fungi.

    According to one current hypothesis, this unikonts may have been the first groups of eukaryotes to diverge from other eukaryotes; however, hypothesis has yet to be widely accepted.

  28. (T/F) Excavates include protists with modified mitochondria and protists with unique flagella.
    True.
  29. (T/F) Most diplomonads and parabasalids of the supergroup Excavata are found in anaerobic environments.

    (T/F) These two groups also lack plastids and have modified mitochondria (until recently, they were thought to lack mitochondria altogether).
    True.

    True.
  30. Diplomonads have modified mitochondria called _________ whereas Parabasalids have reduced mitochondria called ____________.
    mitosomes, hydrogensomes.

    Diplomanads lack functional electron transport chains and hence cannot use oxygen to help extract energy from carbohydrates and other organic molecules. Instead, diplomanads have to get the energy they need from anaerobic biochemical pathways.

    Parabasalids generate some energy anaerobically, releasing hydrogen gas as a by-product.
  31. What are within the supergroup Excavates, group Euglenozoans?
    Kinetoplastids and Euglenids. Euglenozoans differ from Diplomonads and Parabasalids in that they have a crystalline rod of unknown function inside the flagella.
  32. What are kinetoplastids?
    Protists that have a single, large mitochondrion that contains an organized mass of DNA called a kinetoplast.

    They are within the supergroup Excavata and group euglenozoans. These organisms have a spiral or crystalline rod of unknown function within their flagella.

    These protists include spcies that feed on prokaryotes in freshwater, marine and moise terrestrial ecosystems, as well as species that parasitize animals, plants and other protists. Such as Trypanosoma which causes sleeping sickness in humans.
  33. What are euglenids?
    Protists that has a pocket at one end of the cell from which one or two flagella emerge. Many species of the euglenid Euglena are mixotrophs: in sunlight they are autotrophic, but when sunlight is unavailable, they can become heterotrophic, absorbing organic nutrients from their environment.

    Many other euglenids engulf prey by phagocytosis.
  34. Why do some biologists describe the mitochondria of diplomonads and parabasalids as "highly reduced"?
    Their mitochondria do not have an electron transport chain and so cannot function in aerobic respiration.

    This is very important.
  35. (T/F) Chromalveolates may have originiated by secondary endosymbiosis.
    True.
  36. What are Chromalveolata?
    A very large and diverse supergroup of extremely diverse protists and has recently been proposed based on two lines of evidence.

    1) Some (though not all) DNA sequence data suggest that the chromaveolates form a monophyletic group.

    2) Some data support the hypothesis that the chromalveolates originated more than a billion years ago, when a common ancestor of the group engulfed a signle-celled, photosynthetic red alga. Because red alae are thought to have originated by primary endosymbiosis, such an origin for the chromalveolates is ferred to as secondary endosymbiosis.
  37. What are the two best current hypothesis on the clades within Chromalveolates?
    The alveolates and the stramenopiles.
  38. What are the alveolatees?
    A group of protists within the supergroup Chromalveolates (the other group is stramenopiles) whose monophyly is well supported by molecular systematics (forming a clade). Structurally, species in this group have membrane-bound sacs (alveoli) just under the plasma membrane. The function of the alveoli is unknown but it is hypothesized that they may help stablize the cell surface or regulate the cell's water and ion content.

    The alveolates include three subgroups: a group of flagellates (the dinoflagellates), a group of parasites (the apicomplexans) and a group of protists that move using cilia (the ciliates).
  39. What are dinoflagellatees?
    Protists within the supergroup Chromalveolates and the group alveolates.

    These are characterized by cells that are reinforced by cellulose plates. Two flagella located in perpendicular grooves in this "armor" make dinoflagellates sprin as they move through the water. Dinoflagellates are abundant components of both marine and freshwater plankton, communities of microorganisms that live near the water's surface.

    • These dinoflagellates include some of the most important photosynthetic species. However, many photosynthetic dinoflagellates are mixotrophic, and roughly half of the dinoflagellates are purely hterotrophic.
    • Dinoflagellate blooms - episodes of explosive population growth- sometimes cause a phenomenon called "red tide" in coastal waters.
  40. (T/F) The coastal phenomenon called "red tide" in coastal waters are produced by red algae.
    False.

    Dinoflagellate blooms may have originated from secondary endosymbiosis of red alga. Red alga are believed to have originated from primary endosymbiosis.

    Dinoflagellate blooms are episodes of explosive population growth that appear brownish red or pink because of the presence of carotenoids, the most common pigments in dinoflagellate plastids.

    Toxins produced by certain dinoflagellates have caused massive kills of invertebrates and fishes. Humans who eat molluscs that have accumulated the toxins are affected as well, sometimes fatally.
  41. What are apicomplexans?
    Protists within the supergroup Chromalveolates and the group alveolates.

    Nearly all apicomplexans are parasites of animals and some cause serious human diseases. The parasites spread through their host as tiny infectious cells called sporozoites.

    Apicomplexans are so named because one end (the apex) of the sporozoite cell contains a complex of organelles specialized for penetrating host cells and tissues.

    Although apicomplexans are not photosynthetic, recent data has shown that they retain a modified plastid (apicoplast), most likely of red algal origin.

    Most apicomplexans have intricate life cycles with both sexual and asexual stages.
  42. (T/F) Apicomplexans, such as Plasmodium, the parasite that causes malaria lives in both humans and mosquitoes. This parasite reproduces both sexually and asexually.
    True.

  43. (T/F) The search for malarial vaccines has been hampered by the fact that plasmodium lives mainly inside cells, hidden from the host's immune system. Also, like trypanosomes, Plasmodium continually changes its surface proteins.
    True.
  44. What are ciliates?
    Protists within the supergroup Chromalveolates and the group alveolates.

    Ciliates are large, varied group of protists named for their use of cilia to move and feed. The cilia may completely cover the cell surface or may be clustered in a few rows or tufts. In certain species, rows of tightly packed cilia function collectively in locomotion. Other ciliates scurry about on leg-like structures constructed from many cilia bonded together.

    A distinctive feature of ciliates is the presence of two types of nuclei: tiny micronuclei and large macronuclei. A cell has one or more nuclei of each type.

    Genetic variation results from conjugation, a sexual process in which two indivudals exchange haploid micronuclei. Ciliates generally reproduce asexually by binary fission, during which the existing macronucleus disintegrates and a new one is formed from the cell's micronuclei. Each macronucleus typically contains multiple copies of the ciliate's genome.

    Genes in the macronucleus control the everyday functions of the cell, such as feeding, waste removal and maintaing water balance.

  45. (T/F) Ciliates reproduce both sexually and asexually.
    False.

    Genetic variation results from conjugation, a sexual process in which two indivudals exchange haploid micronuclei. Ciliates generally reproduce asexually by binary fission, during which the existing macronucleus disintegrates and a new one is formed from the cell's micronuclei. Each macronucleus typically contains multiple copies of the ciliate's genome.

  46. What are stramenpoiles?
    A group of protists within the supergroup Chromalveolates (the other group is Alveolates). The stramenopiles are a group of marine algae that include some of the most important photosynthetic organisms on the planent, as well clades of heterotrophs.

    Their name (stramen - straw; pilos - hair) refers to their characeristic flagellum, which has numerous fine, hairlike projections. In most stramenopiles, this "hairy" flagellum is paired with a shorter "smooth" (nonhairy) flagellum.

    The group consists of diatoms, golden algae, brown algae, and oomycetes.
  47. What are diatoms?
    Protists within the supergroup Chromalveolates and the group stramenopiles.

    • Diatoms are unicellular algae that have unique glass-like wall made of hydrated silica (silicon dioxide) embedded in an organic matrix. The wall consists of two parts that overlap like a shoe box and its lid. The walls provide effective protection from the crushing jaws of predators.
    • Much of the diatom's strength comes from the delicate lacework of holes and grooves in their walls; if the wallers were smooth, it would take 60% less force to crush them.

    Diatoms reproduce asexually by mitosis; with each daughter cell receives half of the parental cell wall and generates a new half that fits inside it. Some species form cysts as resistant stages. Sexual reproduction occurs but is not common in diatoms.
  48. (T/F) Diatoms reproduce both sexually and asexually.
    False.

    Diatoms reproduce asexually by mitosis; with each daughter cell receives half of the parental cell wall and generates a new half that fits inside it. Some species form cysts as resistant stages. Sexual reproduction occurs but is not common in diatoms.
  49. (T/F) Diatom populations may increase rapidly (bloom) when ample nutrients are available. These blooms cause "red tide" in coastal waters.
    False.

    The first sentence is true but the second sentence is false. Diatom blooms are benefitial in reducing global warming as their bodies incorporate carbon into their bodies from carbon dioxide in the air during photosynthesis. The bodies sink to the ocean floor and are less likely to be broken down by bacteria and other decomposers than those that are eaten.
  50. What are golden algae?
    Protists within the supergroup Chromalveolates and the group stramenopiles.

    Golden algae are typically biflagellated, with both flagella attached near one end of the cell. The characteristic color results from yellow and brown carotenoids.

    Many golden algae are components of freshwater and marine plankton. While all golden algae are photosynthetic, some species are mixotrophic. These mixotrophs can absorb dissolved organic compounds or ingest food particles, including living cells (eukaryotes and prokaryotes) by phagocytosis.

    Most species are unicellular, but some are colonial.
  51. What are brown algae?
    Protists within the supergroup Chromalveolates and the group stramenopiles.

    Brown algae are the most complex and largest algae. All are multicellular and most are marine.

    Brown algae include species have specialized tissues and organs that resemble those in plants. But morphological and DNA evidence indicates that the similarities evolved independently in the algal and plant lineages, and thus are analogous, not homologous.

    A brown algae that is plantlike is known as thallus ( thalli, thallous - sprout). Unlike the body of a plant, a typical thallus consists of a rootlike holdfast, which anchors the alga, and a stemlike stipe, which supports the leaflike blades.

    Brown algae reproduce by alternation of generations - the alternation of multicellular haploid and diploid forms.
  52. (T/F) Brown algae and land plants belong to the same supergroup of Chromalveolata, which explains their similarities.
    False.

    Brown algae belong to the supergroup of Chromalveolata whereas land plants belong to the supergroup of Archaeplastida.

    Brown algae include species have specialized tissues and organs that resemble those in plants. But morphological and DNA evidence indicates that the similarities evolved independently in the algal and plant lineages, and thus are analogous, not homologous.
  53. What is alternation of generations?
    A complex life cycle that includes the alternation of multicellular haploid and diploid forms.
  54. (T/F) The complex life cycle of the brown alga Laminaria provides an example of alternation of generations. The two generations are heteromorphic, meaning that the sporophytes and gametophytes are structurally different.
    The diploid individuals is called the sporophyte because it produces spores. The spores are haploid and move by means of flagella; the flagellated spore are called zoospores. The zoospores develop into haploid male and female gametophytes, which produce gametes. The union of two gametes (fertilization or syngamy) results in a diploid zygote, which matures and gives rise to a new sporophyte.

  55. In alternation of generations, what does it mean if the two generations are heteromorphic or isomorphic?
    In the two generations, for heteromorphic, the sporophytes and gametophytes are structurally different.

    For ismorphic generations, the sporophytes and gametophytes look similar to each other but they differ in chromosome number.
  56. What are oomycetes?
    Protists within the supergroup Chromalveolates and the group stramenopiles.

    Oomycetes include the water molds, the white rusts and the downy mildews. Based on morphology, they were previously classified as fungi but they are not related to fungi and is most likely due to convergent evolution. In both oomycetes and fungi, the high surface-to-volume ratio of filamentous structures enhances the uptake of nutrients from the environment.

    One of the differences includes that oomycetes typically have cell walls made of cellulose, whereas the walls of fungi consist mainly of another polysaccharide, chitin.

    Although oomycetes descended from plastid-beating ancestors, they no longer have plastids and do not perform photosynthesis. Instead, they typically acquire nutrients as decomposers or parasites.

    Most water molds are decomposers. White rusts and downy mildews generally live on land as plant parasites.

  57. Summarize the evidence for and against the hypothesis that the species currently classified as chromoalveolates are members of a single clade.
    Some DNA data indicates that Chromalveolata is a monophyletic group, but other DNA data fail to support this result. In support of monophyly, for many species in the group, the structure of their plastids and the sequence of their plastid DNA suggest that the group originated by a secondary endosymbiosis event (in which a red algae was engulfed). However, other species in the group lack plastids entirely, making the secondary endosymbiosis hypothesis difficult to test.
  58. Which of the three life cycles exhibit alternation of generations? How does it differ from the other two?
    Algae and plants with alternation of generations have a multicellular haploid stage and a multicellular diploid staage.

    In the other two life cycles, either the haploid stage or the diploid stage is unicellular.
  59. (T/F) Rhizarians are a diverse group of protists defined by DNA similarities.
    True.
  60. What is Rhizaria?
    The supergroup Rhizaria that includes the groups chlorarachniophytes, foraminiferans and radiolarians.

    Many species in Rhizaria are among organisms referred to as amoebas. Amoebas were formerly defined as protists that move and feeb by means of pseudopodia, extensions that may bulge from almost anywhere on the cell surface.

    An amoeba moves by extending a psudopodium and anchoring the tip. Amoebas are not only confined within the supergroup Rhizaria and are dispersed across many distantly related eukaryotic taxa. Most that belong to the clade Rhizaria are distinguished morphologically from other amoebas by having threadlike pseudopodia.
  61. What are foraminiferans?
    Protists within the supergroup Rhizarians. These are also known as forams - named for their porous shells, called tests.

    Foram tests consist of a single piece of organic material hardened with calcium carbonate. The pseudopodia that extend through the pores function in swimming, test formation and feeding. Many forams also derive nourishment from photosynthesis of symbiotic algae that live within the tests.

    90% of all identified species of forams are known from fossils.
  62. What are radiolarians?
    Protists within the supergroup Rhizarians.

    These protists have delicate, intricately symmetrical internal skeletons that are generally made of silica. The pseudopodia of these protists radiate from the central body and are reinforced by bundles of microtubules. The microtubules are covered by a thin layer of cytoplasm, which engulfs smaller microorganisms that become attached to pseudopodia.
  63. Explain why forams have such a well-preserved fossil record.
    Because foram tests are hardened with calcium carbonate, they form long-lasting fossils in marine sediments and sedimentary rocks.
  64. What if: DNA evidence suggests that a newly discovered amoeba is in the clade Rhizaria - yet it is more morphology is more similar to amoebas in other eukaryotic groups. Suggest an explanation that could account for these conflicting observations.
    Convergent evolution. The different organisms have come to display similar morphological adaptations over time owning to their similar lifestyles.
  65. (T/F) Red algae and green algae are the closest relative of land plants.
    True.

    Humans and fungi are more closely related than humans and plants or fungi and plants.
  66. What are Archaeplastida?
    A monophyletic supergroup that descended from the ancient protist that engulfed a cyanobaterium.

    The group consists of red algae, green algae and land plants.

    More than a billion years ago, a heterotrophic protist acquired a cyanobaterial endosymbiont, and the photosynthetic descendants of this ancient protist evolved into red algae and green algae. The lineage that produced green algae, gave rise to land plants.
  67. What are red algae?
    Prostis within the supergroup Archaeplastida.

    Red algae are the most abundant large algae in the warm coastal waters of tropical oceans. Their accestory pigments allow them to absorb blue and green light, which penetrate relatively far into the water.

    Most red algae are multicellular, although none are as large as the giant brown kelps.

    The thalli of many red algae are filamentous, often branched and interwoven in lacy patterns. The base of the thallus is usually differentiated as a simple holdfast.

    Red algae have especially diverse life cycles, and alternation of generations is common. Unlike other algae, they have no flagellated stages in their life cycle and depend on the water currents to bring gametes together for fertilization.
  68. What are green algae?
    Protists within the supergroup Archaeplastida.

    Green algae have an ultrastructure and pigment composition much like the chloroplasts of land plants.

    Some systematists advocate including green algae in an expanded "plant" kingdom, Viridiplantae. Phylogenetically, this change makes sense, since otherwise the green algae are a paraphyletic group.

    Green algae are divided into two main groups: chlorophytes and charophyceans.

    Larger size and gereater complexity evolved in chlorophytes by three different mechanisms:

    1) The formation of colonies of individual cells, as seen in Volvox and in filamentous forms that contribute to the stringy masses known as pond scum.

    2) The formation of true multicellular bodies by cell division and differentiation, as seen in the seaweed Ulva

    3) The repeated division of nuclei with no cytoplasmic division, as seen in multinucleate filaments of Caulerpa.
  69. Chlorophytes (within the supergroup Archaeplastida and group green algae) range from unicellular to larger organisms. What are the three different mechanisms for the larger complexity of green algae?
    1) The formation of colonies of individual cells, as seen in Volvox and in filamentous forms that contribute to the stringy masses known as pond scum.

    2) The formation of true multicellular bodies by cell division and differentiation, as seen in the seaweed Ulva

    3) The repeated division of nuclei with no cytoplasmic division, as seen in multinucleate filaments of Caulerpa.
  70. (T/F) Most chlorophytes have complex life cycles, with both sexual and asexual reproductive stages.
    True.

    Nearly all species of chlorophytes reproduce sexually by means of biflagellated gametes that have cup-shaped chloroplasts.

    Alternation of generations have evolved in life cycles of chlorophytes, including Ulva, in which the alternate generations are isomorphic.

  71. Identify two ways in which red algae differ from brown algae.
    Many red algae contain an accessory pigment called phycoerythrin, which gives them a reddish color and allows them to carry out photosythesis in relatively deep coastal water. Also unlike brown algae, red algae have no flagellated stages in their life cycle and must depend on water currents to bring gametes together for fertilization.
  72. Why is it accuate to say that Ulva has true multicellularity but Caulerpa does not?
    Ulva's thallus contains many cells and is differentiated into lifelike blade and roolike holdfast. Caulerpa's thallus is composed of multinucleate filaments without cross-walls, so it is essentially one large cell.

    1) The formation of colonies of individual cells, as seen in Volvox and in filamentous forms that contribute to the stringy masses known as pond scum.

    2) The formation of true multicellular bodies by cell division and differentiation, as seen in the seaweed Ulva

    3) The repeated division of nuclei with no cytoplasmic division, as seen in multinucleate filaments of Caulerpa.
  73. What is Unikonta?
    A recently proposed, extremely diverse supergroup of eukaryotes that includes animals, fungi and some protists.

    There are to major clades of unikonts, the amoebozoans and the opisthokonts (animals, fungi and closely related protist groups).

    The root of the eukaryote phylogenetic tree is unknown but it has been proposed that the unikonts were the first eukaryotes to diverge from eukaryotes. Stechmann and Smith proposed that the supergroup Unikonta did not have DHFR-TS gene fusion while all other supergroups experienced the fusion.
  74. What are amoebozoans?
    A clade within Unikonta that includes many species of amoebas that have lobe- or tube-shaped (rather than thread-like) pseudopodia. Amoebozans include slime molds, gymnamoebas, and entamoebas.
  75. What is a slime mold?
    A group of protists within the supergroup Unikonta and the clade amoebozoan.

    Slime molds, or mycetozoans, were once thought to be fungi because they produce fruiting bodies that aid in spore dispersal. However, the resemblance between slime molds and fungi appears to be an example of evolutionary convergence.

    Slime molds have diverged into two main branches, plasmodial slime molds and cellular slime molds - distinguished in part by their unique life cycles.

    Plasmodial slime molds, the diploid condition is the predominant part of the life cycle, whereas cellular slime molds are haploid organisms. (only the zygote is diploid).
  76. What type of a life cycle does a plasmodial slime mold exhibit? A cellular slime mold? What supergroup are these both categorized in?
    Both are categorized in the Unikonata supergroup under amoebozoan.

    In most plasmodial slime molds, the diploid condition is the predominant part of the life cycle. At one stage of their life cycle, they form a mass called a plasmodium, which is a single mass of cytoplasm that is undivided by plasma membranes and contains many diploid nuclei.



    In cellular slime molds, they are haploid organisms (only the zygote is diploid). Although the mass of cells resembles a plasmodial slime mold, the cells remain separated by their individual plasma membranes.

    They also have fruiting bodies that function in asexual, rather than sexual reporduction.

  77. What are gymnamoebas?
    Protists within the supergroup Unikonta and clade amoebozoans that are unicellular. They exist in soil as well as freshwater and marine environements. Most are heterotrophs that actively seek and consume bacteria and other protists. Some gymnamoebas also feed on detritus (nonliving organic matter).
  78. What are entamoebas?
    Protists within the supergroup Unikonta and clade amoebozoans that are not free-lving (unlike the others), that belong to the genus Entamoeba serving as parasites. They infect all classes of vertebrates as well as some invertebrates.

    Humans are host to at least six species of Entamoeba, but only one, E. histolytica is known to be pathogenic.
  79. What are opisthokonts?
    The clade within Unikonta that includes an extremely diverse group of eukaryotes such as animals, fungi, and several groups of protists.

    Two groups to mention are choanoflagellates which are more closely related to animals than to other protists and nucleariids that are more closely related to fungi than other protists.
  80. Contrast the pseudopodia of ameobozoans and forams.
    Amoebozoans have lobe-shaped pseudopodia, whereas forams have thread-like pseudopodia.
  81. In what sense is "fungus animal" a fitting description of a slime mold? In what sense is it not?
    Slime molds are fungus-like in that they produce fruiting bodies that aid in the dispersal of spores, and they are animal-like in that they are motile and ingest food. However, slime molds are more closely related to gymnamoebas and entamoebas than to fungi or animals.
  82. What two key roles in ecology do protists play?
    Symbiotic and photosynthetic roles that allow for some animals to function or act as important organisms in the biosphere.
  83. What is a "producer"
    An organism that uses energy from light (or inorganic chemicals) to convert carbon dioxide to organic compounds. Producers form the base of ecological food webs.
  84. Justify the claim that photosynthetic protists are amount the most important organisms in the biosphere.
    Because photosynthetic protists lie at the base of aquatic food webs, many aquatic organisms depend on them for food, either directly or indirectly. In addition, a substantial percentage of the oxygen produced in photosynthesis on Earth is made by phtosynthetic protists.
  85. Discuss the range of symbiotic associations that include protists.
    Protists form mutualistic and parasitic symbiotic associations with other organisms. Examples include parabasalids that form a mutualistic symbiosis with termites as well as oomycete Phytophthora ramorum, a symbiotic parasite of oak trees.
  86. What are the eukaryote supergroups?
    Excavates - include protists with modified mitochondria and protists with unique flagella.

    Chromalveolates - may have originated by secondary endosymbiosis

    Rhizarians - a large diverse group of protists defined by DNA similarities

    Archaeplastida - Red algae and green algae are the closest relative of land plants

    Unikonts - include protists that are closely related to fungi and animals.
  87. What are the major clades of Excavates and the key morphological characeristics?
    Diplomonads and parabasalids - modified mitochondria.

    Euglenozoans - spiral or crystalline rode inside flagella
  88. What are the major clades of Chromalveolates and the key morphological characeristics?
    Alveolates - Membrane-bounded sacs (alveoli) beneath plasma membrane

    Stramenopiles - Hairy and smooth flagella
  89. What are the major clades of Rhizarians and the key morphological characeristics?
    Forams - Amoebas with threadlike pseudopodia and a porous shell

    Radiolarians - Amoebas with threadlike pseudopodia radiating from central body
  90. What are the major clades of Archaeplastida and the key morphological characeristics?
    Red algae - Phycoerythrin (accessory pigment)

    Green algae - Plant-type chloroplasts

    Land plants - Tons...
  91. What are the major clades of Unikonts and the key morphological characeristics?
    Amoebozoans - Amoebas with lobe shapped pseudopodia

    Opisthokonts - Tons... (includes fungi and animals.)
  92. Plastids that are surrounded by more than two membranes are evidence of

    a) evolution from mitochondria
    b) fusion of plastids
    c) origin of plastids from archaea
    d) secondary endosymbiosis
    e) budding of the plastids from the nuclear envelope.
    D.
  93. Biologists suspect that endosymbiosis gave rise to mitochondria before plastids partly because

    a) the products of photosynthesis could not be metabolized without mitochondrial enzymes
    b) all eukaryotes have mitochondria (or their remnants) whereas many eukaryotes do not have plastids
    c) mitochondrial DNA is less similar to prokaryotic DNA than is plastid DNA
    d) without mitochondrial CO2 production, photosynthesis could not occur.
    e) mitochondrial proteins are synthesized on cytosolic ribosomes, whereas plastids utilize their own ribosomes.
    B
  94. Which grroup is incorrectly paired with its description?

    a) rhizarians - morphologically diverse group defined by DNA similarities
    b) diatoms - important producers in aquatic communities
    c) red algae - acquired plastids by secondary endosymbiosis
    d) apicomplexans - parasites with intricate life cycles
    e) diplomonads - protists with modified mitochondria
    C
  95. Based on the phylogenetic tree in the figure below, which of the following statements is correct?

    a) The most recent common ancestor is older than that of Chromalveolata
    b) The most recent ancestor of Chromalveolata is older than that of Rhizaria
    c) The most recent common ancestor of red algae and land plants is older than that of nucleariids and fungi.
    d) The most basal (first to diverge) eukaryotic supergroup cannot be determined
    e) Excavata is the most basal eukaryotic supergroup.

    C
  96. Which protists are in the same eukaryotic supergroup as land plants?

    a) green algae
    b) dinoflagellates
    c) red algae
    d) brown algae
    e) both a and c
    E
  97. In life cycles with alternation of generations, multicellular haploid forms alternate with

    a) unicellular haploid forms.
    b) unicellular diploid forms.
    c) multicellular haploid forms
    d) multicellular diploid forms.
    e) multicellular polypoid forms.
    B

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