1. The Origin of the Eukaryotic Cell
The evolution of eukaryotic cells included the following components:
The origin of a flexible cell surface
The origin of a cytoskeleton
The origin of a nuclear envelope
The appearance of digestive vesicles
The endosymbiotic acquisition of certain organelles (mitochondria and chloroplasts)
9+2 arrangement of cilia
multiple chromosomes of linear DNA with organizing proteins, and life cycles with mitosis, meiosis,

2. Cells that live within other cells are called endosymbionts.
The theory of serial endosymbiosis proposes that mitochondria and chloroplasts were formerly small prokaryotes living within larger cells.
Cells that live within other cells are called endosymbionts.
The proposed ancestors of mitochondria were aerobic heterotrophic prokaryotes.
The proposed ancestors of chloroplasts were photosynthetic prokaryotes.
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3. These organelles and bacteria are similar is size.
Several lines of evidence support a close similarity between bacteria and the chloroplasts and mitochondria of eukaryotes.
These organelles and bacteria are similar is size.
Enzymes and transport systems in the inner membranes of chloroplasts and mitochondria resemble those in the plasma membrane of modern prokaryotes.
Replication by mitochondria and chloroplasts resembles binary fission in bacteria.
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4. The single circular DNA in chloroplasts and mitochondria lack histones and other proteins, as in most prokaryotes.
Both organelles have transfer RNAs, ribosomes, and other molecules for transcription of their DNA and translation of mRNA into proteins.
The ribosomes of both chloroplasts and mitochondria are more similar to those of prokaryotes than to those in the eukaryotic cytoplasm that translate nuclear genes.
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5. The Origin of the Eukaryotic Cell
The first step toward the eukaryotic condition may have been the loss of the cell wall by an ancestral prokaryotic cell.
A surface that is flexible enough to allow for infolding lets the cell exchange materials with its environment rapidly enough to sustain a larger volume and more rapid metabolism.
A flexible surface also allows endocytosis so that things could be engulfed
An infolded plasma membrane attached to a chromosome within an ancestral prokaryote may have led to the formation of the nuclear envelope.

6. Figure 28.2 Membrane Infolding

7. Figure 28.3 From Prokaryotic Cell to Eukaryotic Cell (Part 1)

8. Figure 28.3 From Prokaryotic Cell to Eukaryotic Cell (Part 2)

9. Protists Defined
Many members of the Eukarya do not fit into the three familiar kingdoms of the Plantae, Animalia, and Fungi.
The eukaryotes that are neither plants, animals, nor fungi are called protists
Protists constitute a paraphyletic group, and Protista is no longer valid as a kingdom.

10. Fig. 28-03a Figure 28.3 Protist diversity
Diplomonads
Parabasalids
Excavata
Euglenozoans
Dinoflagellates
Alveolates
Apicomplexans
Ciliates
Diatoms
Chromalveolata
Golden algae
Stramenopiles
Brown algae
Oomycetes
Chlorarachniophytes
Forams
Rhizaria
Radiolarians
Red algae
Chlorophytes
Green
algae
Archaeplastida
Charophyceans
Figure 28.3 Protist diversity
For the Cell Biology Video Demonstration of Chemotaxis, go to Animation and Video Files.
Land plants
Slime molds
Amoebozoans
Gymnamoebas
Entamoebas
Nucleariids
Unikonta
Fungi
Opisthokonts
Choanoflagellates
Animals

11. General Biology of the Protists
General Features:
Most protists are aquatic, occupying a variety of environments including marine and fresh waters, the body fluids of other organisms, and soil water.
Most are unicellular, but some are colonial and multicellular, and a few are very large.

12. Protists, the most nutritionally diverse of all eukaryotes, include:
Photoautotrophs, which contain chloroplasts eg. euglena
Heterotrophs, which absorb organic molecules or ingest larger food particles eg. Paramecium, Amoeba
Mixotrophs, which combine photosynthesis and heterotrophic nutrition

13. Some protists are parasitic
Plasmodium causes malaria
Pfesteria shumwayae is a dinoflagellate that causes fish kills
Phytophthora ramorum causes sudden oak death
Phytophthora infestans water mold was the cause of the Irish potato famine
Entamoeba histolytica causes amoeboid dysentery in humans
Giardia lamblia is a parasitic diplomonad that contaminates water supplies and causes giardiasis.
The trypanosomes are human pathogens that cause sleeping sickness (tse tse fly-intermediate host), leishmaniasis, Chagas’ disease, and East Coast fever

14. Figure An Oomycete

15. Figure 28.12 A Parasitic Kinetoplastid

16. General Biology of the Protists
Most protist groups include motile cells due to:
Amoeboid motion involves the formation of pseudopods, extensions of the cell’s constantly changing body mass.
The coordinated beating of tiny, hairlike organelles called cilia can move cells forward or backward.
The eukaryotic flagella move like a whip; some flagella push the cell, while others pull the cell.

17. General Biology of the Protists
Several unicellular protists have the presence of membrane-enclosed vesicles of various types which increases the effective surface area
Several protists that are hypertonic to their environments have contractile vacuoles that excrete excess water.
Food vacuoles are vesicles in which ingested food is digested.

18. Fig. 28-11a Contractile vacuole Oral groove Cell mouth Cilia 50 µm
Micronucleus
Food vacuoles
Macronucleus
Figure Structure and function in the ciliate Paramecium caudatum
(a) Feeding, waste removal, and water balance

19. General Biology of the Protists
The cell surfaces of protists are diverse.
Some protists are surrounded only by a plasma membrane, such as an amoeba or a tough protein coat over the cell membrane called pellicle in Paramecium
Some protists have complex cell walls such as the diatom’s glassy cell walls based on silicone. Certain sedimentary rocks are almost entirely composed of diatom skeletons, called diatomaceous earth.
Some protists have external “shells” such as the foraminiferan’s calcium carbonate shell. The discarded skeletons of ancient foraminiferans make up extensive limestone deposits.

20. Foraminiferans-calcium carbonate shells
Figure Diversity among Protist Cell Surfaces (Part 1)
Foraminiferans-calcium carbonate shells

21. Figure 28.7 Diversity among Protist Cell Surfaces (Part 2)
pellicle

22. Figure 28.18 Diatom Diversity

23. General Biology of the Protists
Most protists practice both asexual and sexual reproduction; some groups practice only asexual.
Asexual reproductive processes in the protists include binary fission, multiple fission, budding, and the formation of spores.
Sexual reproduction in the protists also takes various forms.

24. Conjugation is genetic recombination but no reproduction
Figure Paramecia Achieve Genetic Recombination by Conjugating
Conjugation is genetic recombination but no reproduction

25. Stramenopiles
Brown algae exhibit alternation of generations.
A diploid, spore-producing organism (the sporophyte) gives rise to a haploid, gamete- producing organism (the gametophyte).
In heteromorphic alternation of generations, the generations differ morphologically; in isomorphic alternation of generations, they do not.

26. Figure 28.22 Alternation of Generations

27. Figure 28.26 An Isomorphic Life Cycle

28. Fig
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29. Figure 28.27 A Haplontic Life Cycle

30. Endosymbiosis in Eukaryotic Evolution
There is now considerable evidence that much protist diversity has its origins in endosymbiosis
Mitochondria evolved by endosymbiosis of an aerobic prokaryote
Plastids evolved by endosymbiosis of a photosynthetic cyanobacterium

31. Figure 28.29 A Chloroplast Family Tree (Part 1)

32. Figure 28.29 A Chloroplast Family Tree (Part 2)

33. General Biology of the Protists
Many protists contain endosymbionts.
Endosymbiosis is very common in the protists, and in some cases both the host and the endosymbiont are protists.

34. Photosynthetic dinoflagellate living as endosymbionts with radiolarian
Figure Protists within Protists
Photosynthetic dinoflagellate living as endosymbionts with radiolarian

35. Dinoflagellates,diatoms
Fig
Other
consumers
Herbivorous
plankton
Carnivorous
plankton
Bacteria
absorbed by
Figure Protists are key producers in aquatic communities
Soluble
organic matter
Protistan
Producers
Dinoflagellates,diatoms
secrete

36. Diplomonads and Parabasalids
The diplomonads and the parabasalids appear to represent the earliest surviving branches in today’s tree of eukaryotic life.
Both clades are unicellular organisms that lack mitochondria. Their ancestors possessed mitochondria, but they were lost in the course of evolution.
Giardia lamblia is a parasitic diplomonad that contaminates water supplies and causes giardiasis.
Trichomonas vaginalis is a parabasilid responsible for a sexually transmitted disease in humans.

37. Figure 28.10 Two Protist Groups Lack Mitochondria

38. Euglenozoans
The euglenozoans are a clade of unicellular protists with flagella.
The euglenoids and the kinetoplastids are the two subgroups of the euglenozoans.

39. Euglenozoans
The euglenoids possess flagella arising from a pocket at the anterior end of the cell.
The Euglena propels itself through the water with one of its two flagella.
Many species of Euglena are heterotrophic, whereas others are photoautotrophs.

40. Figure 28.11 A Photosynthetic Euglenoid

41. Euglenozoans
The kinetoplastids are unicellular, parasitic flagellates with a single, large mitochondrion.
The mitochondrion contains a kinetoplast, a unique structure that houses multiple, circular DNA molecules and associated proteins.
The trypanosomes are human pathogens that cause sleeping sickness (tse tse fly-intermediate host), leishmaniasis, Chagas’ disease, and East Coast fever.

42. Alveolates
The alveolates are a clade of unicellular organisms characterized by the possession of cavities called alveoli just below their plasma membranes.
Alveolates include the subgroups dinoflagellates, apicomplexans, and the ciliates.

43. Alveolates
The dinoflagellates are unicellular, aquatic organisms; they are among the most important primary producers in the oceans.
Many dinoflagellates are endosymbionts, while some live as parasites within other marine organisms.
The dinoflagellates have a distinctive appearance with two flagella.
They are responsible for toxic “red tides.”
Many are bioluminescent.

44. Figure 28.13 A Red Tide of Dinoflagellates

45. Alveolates
The apicomplexans are exclusively parasitic.
The apical complex is a mass of organelles contained within the apical end of their spores. These organelles help the apicomplexan spore invade its host tissue.
Apicomplexans of the genus Plasmodium are the cause of malaria.
This parasite enters the human circulatory system by way of the Anopheles mosquito.
Toxoplasma, a genus of apicomplexans, is also a pathogenic.

46. Figure 28.14 The Life Cycle of an Apicomplexan

47. Alveolates
The ciliates are named for their characteristic hairlike cilia.
Almost all are heterotrophic, and they have a complex body form.
The ciliates possess two types of nuclei: a single macronucleus and one or more micronuclei.
The micronuclei are typical eukaryotic nuclei.
The macronuclei are derived from the micronuclei and contain DNA that is transcribed and translated to regulate the life of the cell.

48. Figure 28.15 Diversity among the Ciliates (Part 1)

49. Alveolates
Paramecium is a frequently studied ciliate.
The cell is covered by an elaborate pellicle composed of an outer membrane and an inner layer of membrane-enclosed alveoli that surround the bases of the cilia.
Defensive trichocysts in the pellicle are expelled in response to threat.
The cilia on a Paramecium provide a form of locomotion that is more precise than locomotion by flagella or pseudopods.

50. Figure 28.16 Anatomy of Paramecium

51. Alveolates
Paramecia reproduce asexually by binary fission, in which the micronuclei divide mitotically and the macronuclei divide by an unknown mechanism.
Paramecia also exhibit a form of genetic recombination called conjugation. It is not a reproductive process; no new cells are created.
Each member of a pair of cells gets two haploid micronuclei, which fuse to form a new diploid micronucleus.
Experiments have shown that in species not permitted to conjugate, the clones can survive only a limited number of divisions.

52. Stramenopiles
The stramenopiles typically have two flagella of unequal length at some point in their life cycle.
The longer of the two flagella bears rows of tubular hairs.
Some stramenopiles lack flagella, but are presumed to be descended from ancestors that had flagella.
The stramenopiles include the diatoms, the brown algae (photosynthetic), and the oomycetes.

53. Stramenopiles
Diatoms are single-celled organisms, but some species form filaments. Diatoms have carotenoids in their chloroplasts to give them a yellow or brownish color.
Diatoms deposit silicon in their cells walls, which gives them their characteristically intricate appearance.
Certain sedimentary rocks are almost entirely composed of diatom skeletons, called diatomaceous earth.
Diatoms reproduce both sexually and asexually.
Diatoms are major photosynthetic producers in coastal waters and in fresh waters.

54. Stramenopiles
The brown algae are multicellular organisms composed of either branched filaments or leaflike growths called thalli.
The carotenoid pigment fucoxanthin in the chloroplasts gives brown algae their color.
The brown algae are exclusively marine, and most are attached to rocks near the shore.
The holdfast is a specialized structure that glues the attached forms to rocks. Brown algae include the larget of the protists (giant kelps-60 meters long)
Some brown algae have stalks and blades, and some develop gas-filled cavities or bladders. In addition to organ differentiation they are also seen to have some tissue differentiation.
Their cell walls (made up of polymer of sugar acids) are used commercially.

55. Figure 28.21 Brown Algae in a Turbulent Environment
Sea palms
holdfast

56. Stramenopiles
The oomycetes are a nonphotosynthetic group that consists largely of the water molds and their terrestrial relatives, such as the downy mildews.
The oomycetes are coenocytes (many nuclei enclosed in a single plasma membrane).
The oomycetes are diploid for most of their life cycle and have flagellated reproductive cells.
The water molds are aquatic and saprobic (they feed on dead organic matter).
Most terrestrial oomycetes are decomposers, although some are serious plant parasites.
Phytophthora infestans water mold was the cause of the Irish potato famine.

57. Red Algae
Almost all red algae are multicellular.
Their characteristic red color results from the photosynthetic pigment phycoerythrin.
Most species of red algae are marine-dwelling, from shallow tide pools to deep in the ocean.
The red algae have the ability to change the relative amounts of their various photosynthetic pigments depending on the light conditions.

58. Figure Red Algae

59. Red Algae
The red algae have characteristics that make them unique among protists.
They contain the pigments phycoerythrin and phycocyanin and store the products of photosynthesis as floridean starch (small chains of glucose)
They produce no motile, flagellated cells at any stage in their life cycle.
Some produce a mucilaginous polysaccharide substance which is the source of agar.

60. Chlorophytes
The chlorophytes are a monophyletic group with a sister lineage consisting of other green algal lineages and the plant kingdom.
Like plants, the chlorophytes contain chlorophylls a and b, and store photosynthetic products as starch in plastids.
There are terrestrial, marine, and freshwater chlorophyte species.
There is an incredible variety in shape and construction of the algal body within the chlorophytes.

61. Most of the 7,000 species of chlorophytes live in freshwater.
Other species are marine, inhabit damp soil or snow, or live symbiotically within other eukaryotes.
Some chlorophytes live symbiotically with fungi to form lichens, a mutualistic collective.
Some examples: chlamydomonas, volvox, spirogyra
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62. Figure 28.25 Chlorophytes (Part 2)
(sea lettuce)

63. Chlorophytes
There is great diversity within the life cycles of the chlorophytes.
The sea lettuce Ulva lactuca exhibits an isomorphic life cycle.
Most species of Ulva have structurally indistinguishable male and female gametes, and are categorized as isogamous.

64. Chlorophytes
Other chlorophytes are anisogamous, having female gametes that are distinctly larger than male gametes.
Many other chlorophytes have a heteromorphic life cycle, with some exhibiting a variation of the heteromorphic life cycle called the haplontic life cycle (only zygote is diploid)
Other chlorophytes have a diplontic life cycle like that of many animals, where every cell except the gametes is diploid.

65. Chlorophytes
There are green algae other than chlorophytes.
The chlorophytes are the largest lineage of green algae, but there are other lineages as well.
These lineages are branches of a lineage that also includes the charophytes and the plant kingdom.

66. A History of Endosymbiosis
Chloroplasts are found in many distantly related protist lineages.
Some of these groups differ from others in terms of the photosynthetic pigments in their chloroplasts and the number of membranes surrounding their chloroplasts.
These differences can be traced back to whether the group acquired its chloroplast through primary, secondary, or tertiary endosymbiosis.

67. Choanoflagellates
The choanoflagellates are a group of colonial, flagellated protists that are thought to comprise the closest relatives of the animals.
Choanoflagellates bear a striking resemblance to the most characteristic type of cell found in the sponges.

68. Figure 28.28 A Link to the Animal Kingdom

69. Some Recurrent Body Forms
A diversity of protists use pseudopodia for movement and feeding
The amoeboid body plan includes pseudopods for locomotion.
Amoebas appear in many protist groups.
Amoebas are specialized protists: many are adapted for life on the bottoms of lakes, ponds, and other bodies of water.
Most are predators, parasites, or scavengers. A few are photosynthetic.
Some amoebas have shells.

70. Some are all unicellular and use pseudopodia to move and to feed.
Pseudopodium emerge from anywhere in the cell surface.
Amoeboid movement is driven by changes in microtubules and microfilaments in the cytoskeleton.
To move, an amoeba extends a pseudopod, anchors its tip, and then streams more cytoplasm into the pseudopodium.
Fig
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71. Some are important parasites.
These include Entamoeba histolytica which causes amoeboid dysentery in humans.
These organisms spread via contaminated drinking water, food, and eating utensils.
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72. Some Recurrent Body Forms
The actinopods are have thin, stiff pseudopods, reinforced by microtubules. Their silicone skeletons seen as ooze in ocean sea floor
The pseudopods increase the surface area of the cell, help the cell float, provide locomotion in some species, and are the cell’s feeding organs.
Radiolarians are exclusively marine and secrete a glassy endoskeleton.
Heliozoans are primarily freshwater actinopods that lack an endoskeleton.

73. Figure Two Actinopods

74. Some Recurrent Body Forms
Foraminiferans are marine protists that secrete shells of calcium carbonate.
The parent shell is abandoned after foraminiferan reproduction. The discarded skeletons of ancient foraminiferans make up extensive limestone deposits.
The shells of individual foraminiferan species have been preserved as fossils in marine sediments and are valuable as indicators in the classification and dating of sedimentary rocks.

75. All ingest particulate food by endocytosis.
Slime molds have structural adaptations and life cycles that enhance their ecological roles as decomposers
Mycetozoa (slime molds or “fungus animals”) are neither fungi nor animals, but protists.
Any resemblance to fungi is analogous, not homologous, for their convergent role in the decomposition of leaf litter and organic debris.
Slime molds (plasmodial or cellular) feed and move via pseudopodia, like amoeba, but comparisons of protein sequences place slime molds relatively close to the fungi and animals. Slime molds share only general characteristics:
All are motile.
All ingest particulate food by endocytosis.
All form spores on erect fruiting bodies.

76. The plasmodial slime molds (Myxogastrida) are brightly pigmented, heterotrophic organisms.
The feeding stage is an amoeboid mass (not multicellular but a single mass of cytoplasm with multiple nuclei; coenocytic), the plasmodium, that may be several centimeters in diameter.
In unfavorable conditions they either form an irregular mass (sclerotium) or fruiting structures (sporangiophores) which gives off haploid spores which can become swarm cells and be independent or fuse and then divide to become a new plasmodium

77. Figure 28.31 (b) Acellular Slime Molds

78. The feeding stage consists of solitary cells.
The cellular slime molds (Dictyostelida) straddle the line between individuality and multicellularity.
The feeding stage consists of solitary cells.
When food is scarce, the cells form an aggregate (“slug”) that functions as a unit.
Each cell retains its identity in the aggregate.
The dominant stage in a cellular slime mold is the haploid stage while the diploid stage is the dominant stage in palsmodium slime molds
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79. Figure 28.32 A Cellular Slime Mold