1. Eukaryotic Cell Biology and Eukaryotic Microorganisms
Chapter 20
Eukaryotic Cell Biology and Eukaryotic Microorganisms

2. I. Eukaryotic Cell Structure and Function
20.1 Eukaryotic Cell Structure and the Nucleus
20.2 The Mitochondrion and Hydrogenosome
20.3 The Chloroplast
20.4 Endosymbiosis: Relationships of Mitochondria and Chloroplasts to Bacteria
20.5 Other Organelles and Eukaryotic Cell Structures
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3. 20.1 Eukaryotic Cell Structure and the Nucleus
Eukaryotes
Contain a membrane-enclosed nucleus and other organelles (e.g., mitochondria, Golgi complex, peroxisomes, endoplasmic reticula, microtubules, and microfilaments; Figure 20.1)
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4. Smooth endoplasmic reticulum
Figure 20.1
Smooth endoplasmic reticulum
Microtubules
Rough endoplasmic reticulum
Mitochondrion
Flagellum
Cytoplasmic membrane
Ribosomes
Mitochondrion
Microfilaments
Peroxisome
Lysosome
Figure 20.1 Cutaway schematic of a eukaryotic cell.
Golgi complex
Chloroplast
Nucleus
Nuclear envelope
Nuclear pores
Nucleolus
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5. 20.1 Eukaryotic Cell Structure and the Nucleus
Nucleus: contains the chromosomes (Figure 20.2)
DNA is wound around histones
Visible under light microscope without staining
Enclosed by two membranes
Within the nucleus is the nucleolus
Site of ribosomal RNA synthesis
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6. Nucleus Nuclear pores Vacuole Lipid vacuole Mitochondria Figure 20.2
Figure 20.2 The nucleus.
Mitochondria
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7. 20.2 The Mitochondrion and Hydrogenosome
Both specialize in chemotrophic energy metabolism
Mitochondrion (Figure 20.3)
Respiration and oxidative phosphorylation
Bacterial dimensions (rod or spherical)
Over 1,000 per animal cell
Surrounded by two membranes
Folded internal membrane called cristae
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8. Inner membrane Cristae Matrix Porous outer membrane Figure 20.3
Figure 20.3 Structure of the mitochondrion.
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9. 20.2 The Mitochondrion and the Hydrogenosome
Hydrogenosome (Figure 20.4)
Similar size to mitochondria, however, lack TCA cycle enzymes and cristae
Oxidation of pyruvate to H2, CO2, and acetate
Trichomonas and various ciliated protists have hydrogenosomes
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10. Figure 20.4 Cell membrane Cytoplasm Figure 20.4 The hydrogenosome.
Glycolysis
Figure 20.4 The hydrogenosome.
Hydrogenosome
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11. 20.3 The Chloroplast Chloroplast (Figure 20.5)
Chlorophyll-containing organelle found in phototrophic eukaryotes
Size, shape, and number of chloroplasts varies
Flattened membrane discs are thylakoids (Figure 20.6)
Lumen of the chloroplast is called the stroma
Stroma contains large amounts of RubisCO
RubisCO is key enzyme in Calvin cycle
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12. Figure 20.5
Figure 20.5 Photomicrographs of protist and green alga cells showing chloroplasts.
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13. Thylakoid Chloroplast Figure 20.6 Figure 20.6 The chloroplast.
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14. 20.4 Relation of Mitochondria & Chloroplasts to Bacteria
Chloroplasts and mitochondria suggested as descendants of ancient prokaryotic cells (primary endosymbiosis)
Evidence that supports idea of endosymbiosis
Mitochondria and chloroplasts contain DNA (Figure 20.7)
Eukaryotic nuclei contain genes derived from bacteria
Mitochondria and chloroplasts contain own ribosomes
Antibiotic specificity
Molecular phylogeny
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15. Mitochondria Nucleus Figure 20.7
Figure 20.7 Cells of the ascomycete yeast Saccharomyces cerevisiae.
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16. 20.4 Relation of Mitochondria & Chloroplasts to Bacteria
Secondary endosymbiosis: the process of engulfing a green or red algal cell, retaining its chloroplast, and becoming phototrophic
Euglenids and chlorarachniophytes (green algae)
Alveolates and stramenopiles (red algae)
Molecular evidence of tertiary symbiosis also exists
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17. 20.5 Other Organelles and Eukaryotic Cell Structures
Endoplasmic reticulum (ER)
Two types of ER (smooth and rough)
Rough contains attached ribosomes, smooth does not
Smooth ER participates in the synthesis of lipids
Rough ER is a major producer of glycoproteins
Golgi complex (Figure 20.8): stacks of membrane distinct from, but functioning in concert with, the ER
Modifies products of the ER destined for secretion
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18. Figure 20.8 Figure 20.8 The Golgi complex.
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19. 20.5 Other Organelles and Eukaryotic Cell Structures
Lysosomes
Membrane-enclosed compartments
Contain digestive enzymes used for hydrolysis
Allow for lytic activity to occur within the cell without damaging other cellular components
Peroxisomes
Oxidize various compounds
Examples: alcohols, fatty acids, toxins
Also function in synthesis of bile salts
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20. 20.5 Other Organelles and Eukaryotic Cell Structures
Microfilaments (Figure 20.9)
7 nm in diameter, polymers of actin
Function in maintaining cell shape, motility by pseudopodia, and cell division
Microtubules (Figure 20.10)
25 nm in diameter, composed of - and -tubulin
Function in maintaining cell shape, in motility, in chromosome movement, and in movement of organelles
Intermediate filaments
8–12 nm in diameter, keratin proteins
Function in maintaining cell shape and positioning of organelles in cell
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21. Microfilaments Figure 20.9
Figure 20.9 Microfilaments and eukaryotic cell architecture.
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22. Figure 20.10 Figure 20.10 Tubulin of Tetrahymena thermophila.
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23. 20.5 Other Organelles and Eukaryotic Cell Structures
Flagella and cilia (Figure 20.11)
Organelles of motility allowing cells to move by swimming
Cilia are short flagella
Structurally distinct from prokaryotic flagella
Bundle of nine pairs of microtubules surrounding the axoneme
Require ATP
Propel the cell using a whiplike motion
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24. Figure 20.11
Flagella
Cilia
Figure Motility organelles in eukaryotic cells: Flagella and cilia.
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25. II. Eukaryotic Microbial Diversity
20.6 Phylogeny of the Eukarya
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26. 20.6 Phylogeny of the Eukarya
18S rRNA genes for phylogeny of eukaryotes
Relationship of 18S rRNA genes is much less strong for eukaryotes than 16S rRNA genes are for prokaryotes
Phylogenies have been constructed using other genes (e.g., tubulin, RNA polymerase, and ATPase)
New insights have arisen because of these new phylogenies (e.g., fungi and animals are closely related)
Eukaryotic molecular phylogeny is still being refined
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27. Protists Figure 20.12 Bacteria Stramenopiles Alveolates Cercozoans
Oomycetes
Brown algae
Diatoms
Golden algae
Radio- larians
Cercozoans
Ciliates
Alveolates
Chlorarach- niophytes
Dinoflagellates
Foramin- iferans
Apicomplexans
Parabasalids
Red algae
Diplomonads
Green algae
(Secondary endosymbioses)
Kinetoplastids
Plants
Euglenozoa
Euglenids
Cellular slime molds
Plasmodial slime molds
Figure Phylogenetic tree of Eukarya.
Entamoebas
Amoebozoa
Gymnamoebas
Chloroplast ancestor (primary endosymbiosis)
Animals
Mitochondrial ancestor (primary endosymbiosis)
Fungi
Fungi
Microsporidia
Bacteria
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28. III. Protists 20.7 Diplomonads and Parabasalids 20.8 Euglenozoans
Alveolates
20.10 Stramenopiles
20.11 Cercozoans and Radiolarians
20.12 Amoebozoa
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29. 20.7 Diplomonads and Parabasalids
Key genera: Giardia, Trichomonas
Diplomonads (Figure 20.13a)
Have two nuclei of equal size
Have mitosomes
Cause of giardiasis, a common waterborne disease
Parabasalids (Figure 20.13b)
Contain a parabasal body
Lack mitochondria, but have hydrogenosomes for anaerobic metabolism
Genomes lack introns
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30. Figure 20.13 Figure 20.13 Diplomonads and parabasalids.
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31. 20.8 Euglenozoans Key genera: Trypanosoma, Euglena
Unicellular flagellated eukaryotes
Have a crystalline rod in their flagella
Kinetoplastids
Named for the presence of the kinetoplast, a mass of DNA present in their single large mitochondrion
Live primarily in aquatic habitats feeding on bacteria
Some species cause serious diseases in humans
For example, Trypanosoma causes African sleeping sickness (Figure 20.14)
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32. Membrane flap Trypanosome cell Red blood cell Figure 20.14
Figure Trypanosomes.
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33. 20.8 Euglenozoans Euglenids (Figure 20.15)
Nonpathogenic and phototrophic
Contain chloroplasts, can exist as heterotrophs
Can feed on bacteria by phagocytosis
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34. Figure 20.15 Figure 20.15 Euglena, a euglenozoan.
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35. 20.9 Alveolates Key genera: Gonyaulax, Plasmodium, Paramecium
Alveolates characterized by presence of alveoli, which are sacs underneath the cytoplasmic membrane
May function to help cells maintain osmotic balance
Members are ciliates, dinoflagellates, and apicomplexans
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36. 20.9 Alveolates Ciliates Possess cilia at some stage of their life
Most widely distributed genera are Paramecium (Figure 20.16)
Use cilia for motility and to obtain food
Ciliates have two nuclei (macronucleus and micronucleus)
During conjugation two paramecia exchange micronuclei
Some ciliates are animal parasites (Figure 20.17)
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37. Yeast cell (for scale) Cilia Mouth (gullet) Figure 20.16
Figure Paramecium, a ciliated protist.
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38. Figure 20.17
Figure Balantidium coli, a ciliated protist that causes a dysentery-like disease in humans.
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39. 20.9 Alveolates Dinoflagellates (Figure 20.18)
Diverse marine and freshwater phototrophic organisms
Have two flagella with different insertion points on the cell
Some are free-living and others live symbiotically with corals
Dense suspensions of these cells are called red tides (Figure 20.19)
Associated with fish kills and human poisoning (PSP)
Pfiesteria piscicida is a genus of toxic dinoflagellate responsible for massive fish kills
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40. Figure 20.18
Figure The marine dinoflagellate Ornithocercus magnificus (an alveolate).
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41. Figure 20.19 Figure 20.19 Toxic dinoflagellates (alveolates).
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42. 20.9 Alveolates Apicomplexans (Figure 20.20)
Obligate parasites of animals
Cause severe diseases such as malaria, toxoplasmosis, and coccidiosis
Contain apicoplasts
Degenerate chloroplasts that lack pigments and phototrophic capacity
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43. Figure 20.20 Figure 20.20 Apicomplexans.
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44. 20.10 Stramenopiles Key genera: Phytophthora, Nitzschia, Dinobryon
Oomycetes, diatoms, golden algae, and brown algae
All have many short hairlike extensions
Chemoorganotrophic and phototrophic members
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45. 20.10 Stramenopiles Oomycetes
Also called water molds based on their filamentous growth and the presence of coenocytic hyphae
Cell walls are made of cellulose, not chitin as in fungi
Phytophthora infestans causes the late blight disease in potatoes and contributed to the Irish potato famine
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46. 20.10 Stramenopiles Diatoms (Figure 20.21)
Over 100,000 species of diatoms
Freshwater and marine habitats
Cell walls are made of silica and are called frustules
Exhibit radial and pennate symmetry
Appeared on Earth about 200 million years ago
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47. Figure 20.21 Figure 20.21 Diatom frustules.
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48. 20.10 Stramenopiles Golden algae Also called chrysophytes
Most are unicellular
Some are colonial
Golden algae are named because of their golden-brown color
Chloroplast pigments dominated by fucoxanthin
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49. 20.11 Cercozoans and Radiolarians
Distinguished from other protists by their threadlike pseudopodia
Cercozoans (Figure 20.22)
Include the chlorarachniophytes and foraminifera
Chlorarachniophytes
Phototrophic amoeba-like organism that has a flagellum for dispersal
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50. Figure 20.22 Figure 20.22 A foraminiferan (a cercozoan).
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51. 20.11 Cercozoans and Radiolarians
Cercozoans (cont’d)
Foraminifera
Exclusively marine organisms
They form shell-like structures called tests
Tests are made from organic materials reinforced with calcium carbonate
White Cliffs of Dover are formed from fossilized foraminifera tests
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52. 20.11 Cercozoans and Radiolarians
Mostly marine, heterotrophic organisms
Tests are made of silica
Name is derived from radial symmetry of tests
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53. 20.12 Amoebozoa Key genera: Amoeba, Entamoeba, Physarum, Dictyostelium
Terrestrial and aquatic protists that use pseudopodia for movement and feeding (Figure 20.23)
Major groups are gymnamoebas, entamoebas, and slime molds
Gymnamoebas
Free-living, inhabit soil and aquatic environments
Move by amoeboid movement (cytoplasmic streaming)
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54. Figure 20.23
Figure Time-lapse view of the motile amoebozoan Amoeba proteus.
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55. 20.12 Amoebozoa Entamoebas Slime molds (Figure 20.24)
Parasites of vertebrates and invertebrates
Slime molds (Figure 20.24)
Previously grouped with fungi because they have similar life cycle (Figure 20.25)
Motile, can move across surfaces rapidly
Two groups of slime molds: plasmodial and cellular
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56. Figure 20.24
Figure Slime mold.
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57. Figure 20.25
Figure Photomicrographs of various stages in the life cycle of the cellular slime mold Dictyostelium discoideum.
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58. 20.12 Amoebozoa Plasmodial slime molds
Have vegetative forms that are masses of protoplasm of indefinite size and shape (plasmodium)
Cellular slime molds (Figure 20.26)
Vegetative forms composed of single amoebae
Form diploid macrocysts
Aggregate as a pseudoplasmodium
Fruiting body is formed
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59. Aggregation of amoebae
Figure 20.26
1.2
Mature fruiting body
1.0
Height (mm)
0.8
Aggregation of amoebae
0.6
0.4
0.2 A 1 G H B F I 2 D E J C K L 3 M
Slug migration 4
Fruiting body formation
Figure Stages in fruiting body formation in the cellular slime mold Dictyostelium discoideum.
Time (h) 5
Extent of cellular differentiation 6 7 8
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60. IV. Fungi 20.13 Fungal Physiology, Structure, and Symbioses
20.14 Fungal Reproduction and Phylogeny
20.15 Chytridiomycetes
20.16 Zygomycetes and Glomeromycetes
20.17 Ascomycetes
20.18 Basidiomycetes and the Mushroom Life Cycle
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61. 20.13 Fungal Physiology, Structure, and Symbioses
Most fungi are multicellular, forming a network of hyphae
Hyphae that extend above the surface can produce asexual spores called conidia (Figure 20.27)
Conidia are often pigmented and resistant to drying
Hyphae form compact tufts called mycelia (Figure 20.28)
Most fungal cell walls are made of chitin
Mycorrhizae help plant roots obtain phosphorus
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62. Germination Conidia (spores) Conidiophore Aerial hyphae Subsurface
Figure 20.27
Germination
Conidiophore
Conidia (spores)
Aerial hyphae
Subsurface
Hyphae
Figure Fungal structure and growth.
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63. Figure 20.28
Figure Fungi.
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64. 20.13 Fungal Physiology, Structure, and Symbioses
Some fungi produce macroscopic reproductive structures called fruiting bodies (Figure 20.29)
Mushrooms and puffballs are fruiting bodies
Fungi can cause disease in plants and animals
Dutch elm trees were devastated by fungal infection of the ascomycete Ophiostoma ulmi
Mycoses in humans range in severity from “athlete’s foot” to histoplasmosis
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65. Basidiocarp Basidiospores Spore germination Mature mushroom
Figure 20.29
Basidiocarp
Basidiospores
Figure Mushroom life cycle.
Spore germination
Mature mushroom
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66. 20.14 Fungal Reproduction and Phylogeny
Most fungi reproduce by asexual means (three forms)
Growth and spread of hyphal filaments
Asexual production of spores
Simple cell division (budding yeasts; Figure 20.30)
Some fungi produce spores as a result of sexual reproduction
Sexual spores can originate from the fusion of two haploid cells to form a diploid cell (ascospores, basidiospores, zygospores)
Spores are resistant to drying, heating, freezing, chemicals
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67. Figure 20.30
Figure Scanning electron micrograph of the common baker’s and brewer’s yeast Saccharomyces cerevisiae (ascomycetes).
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68. 20.14 Fungal Reproduction and Phylogeny
Fungi share a more recent common ancestor with animals than any other group of eukaryotic organisms
Estimated that fungi and animals diverged 1.5 billion years ago
Earliest fungal lineage is thought to be chytridiomycetes (Figure 20.31)
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69. Batrachochytrium Rhizopus Glomus Saccharomyces Amanita Figure 20.31
Chytridiomycetes
Batrachochytrium
Zygomycetes
Rhizopus
Glomeromycetes
Glomus
Figure Phylogeny of fungi.
Ascomycetes
Saccharomyces
Basidiomycetes
Amanita
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70. 20.15 Chytridiomycetes Key genera: Allomyces, Batrachochytrium
“Chytrids” are the earliest diverging line of fungi
Commonly found in moist soil and freshwater
Some are colonial and some are unicellular
Implicated in the massive die-off of amphibians (Figure 20.32)
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71. Chytrid cells Frog epidermis Figure 20.32
Figure Chytridiomycetes.
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72. 20.16 Zygomycetes and Glomeromycetes
Key genera: Rhizopus, Encephalitozoon
Known primarily for food spoilage
Commonly found in soil and decaying plant material
All are coenocytic
All form zygospores
Rhizopus stolonifer (a black bread mold) is representative (Figure 20.33)
Microsporidia: unicellular, obligate parasites
Often infect immune-compromised individuals (e.g., AIDS patients)
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73. Figure 20.33 Figure 20.33 Zygomycetes and microsporidia.
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74. 20.16 Zygomycetes and Glomeromycetes
Small group of fungi that have major ecological importance
All known species form endomycorrhizae with the roots of herbaceous plants
In some cases also with woody plants
None have grown independently of a plant
Only reproduce asexually
Thought to have played important role in ability of early vascular plants to colonize land
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75. 20.17 Ascomycetes Key genera: Saccharomyces, Candida, Neurospora
Highly diverse, baker’s yeast to bread molds
Found in aquatic and terrestrial environments
Decompose dead plant material, some are lichen symbionts
Saccharomyces cerevisiae
Cells are spherical to oval, cell division through budding (Figure 20.34)
Flourish in habitats where sugars are present
Sexual reproduction process called mating
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76. Figure 20.34
Bud
Figure Growth by budding division in Saccharomyces cerevisiae.
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77. 20.17 Ascomycetes
There are two mating types in Saccharomyces cerevisiae (Figure 20.35)
Yeast cells can switch from one type to another by a genetic switch mechanism (Figure 20.36)
Animation: Life Cycle and Mating Types in Typical Yeast
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78. Haploid (1n) Diploid (2n)
Figure 20.35
Mating
Cell fusion
Nuclear fusion  a a 
Asexual reproduction (mitosis) a 
Haploid (1n)
Diploid (2n)
Asexual reproduction (mitosis)
Figure Life cycle of a typical ascomycete yeast, Saccharomyces cerevisiae.
Germination
Meiosis
Ascospores (haploid)
Ascus
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79. Silent -type master gene
Figure 20.36
Silent -type master gene
Promoter
Silent a-type master gene
MAT locus
Cell is mating type 
-type gene
Mating type switch
Discarding of -type gene
Copy of a-type gene
Figure The cassette mechanism that switches an ascomycete yeast from mating type  to a.
Cell is mating type a
a-type gene
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80. 20.18 Basidiomycetes and the Mushroom Life Cycle
Key genera: Agaricus, Amanita
Over 30,000 described species
Many are recognizable as mushrooms and toadstools
Also yeasts and pathogens of plants and humans
Undergo both vegetative and sexual reproduction
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81. V. Red and Green Algae 20.19 Red Algae 20.20 Green Algae
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82. 20.19 Red Algae Key genus: Cyanidioschyzon
Red algae are also called rhodophytes
Mostly marine, but some freshwater and terrestrial
Red color is from phycoerythrin, an accessory pigment (Figure 20.39)
At greater depth, more phycoerythrin is produced by cells
Cyanidioschyzon merolae are unusually small (1–2  m in diameter)
16.5-Mbp genome is one of smallest for phototrophic eukaryotes
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83. Figure 20.39 Figure 20.39 Polysiphonia, a marine red alga.
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84. 20.20 Green Algae Key genera: Chlamydomonas, Volvox
Green algae are also called chlorophytes
Closely related to plants
Most green algae inhabit freshwater, but some are marine or terrestrial
Can be unicellular to multicellular (Figure 20.41)
Have sexual and asexual reproduction
Endolithic algae grow inside porous rocks (Figure 20.42)
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85. Figure 20.41
Figure Light micrographs of representative green algae.
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86. Figure 20.42 Figure 20.42 Endolithic phototrophs.
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