Unicellular Eukaryotes

1. Unicellular Eukaryotes Chapter 11

2. Emergence of Eukaryotes • First evidence of life dates to 3.5 billion years ago. • First cells were bacteria-like.

3. Emergence of Eukaryotes • Origin of complex eukaryote cells • Most likely symbiosis among prokaryotic cells. • Modification of engulfed prokaryote into an organelle: Primary endosymbiosis. • Aerobic bacteria engulfed by bacteria. • May have become mitochondria found in most modern eukaryotic cells. • Engulfed photosynthetic bacteria evolved into chloroplasts. • Descendants in green algae lineage gave rise to multicellular plants.

4. Emergence of Eukaryotes • Other groups apparently originated by secondary endosymbiosis. • One eukaryotic cell engulfed another eukaryotic cell and the latter became transformed into an organelle.

5. Protozoans • Protozoans are an extremely diverse assortment of unicellular eukaryotes.

6. Protozoans • Protozoa • Lack a cell wall • Have at least one motile stage in life cycle • Most ingest their food • Carry on all life activities within a single cell. • Can survive only within narrow environmental ranges. • Very important ecologically. • At least 10,000 species of protozoa are symbiotic in or on other plants or animals. • Relationships may be mutualistic, commensalistic, or parasitic.

7. Protozoans • Protozoans are more diverse than all other eukaryotes. • No longer classified in a single kingdom. • Recently shown that there are at least seven or more clades. • May be more than 60 monophyletic eukaryotic clades. • “Protozoa” is now used informally without implying phyletic relationship.

8. Cladogram of the Major Divisions of Organisms

9. Nutrition in Protozoans • Autotrophs - contain chloroplasts. • Heterotrophs - absorb organic molecules or ingest larger food particles. • Phagocytosis • Mixotrophs - combine photosynthesis and heterotrophic nutrition.

10. Protozoans Occur in Diverse Habitats • Freshwater and marine species. • Require moisture • Free-living and symbiotic species. • Mutualistic – benefits both. • Commensalistic – one benefits, the other is neutral. • Parasitic – one benefits at a cost to the other.

11. Locomotion in Protozoans • Protists have three main methods of locomotion. • Some protists, like this Euglena, have one or two long flagella that they can whip around an propel themselves through the water. http://www.youtube.com/watch?v=jl0TzaWUQWk

12. Locomotion in Protozoans • Some, like this Tetrahymena, are covered with numerous, but shorter, cilia that facilitate movement and/or feeding. http://www.youtube.com/watch?v=ApjDSGZWHsw

13. Locomotion in Protozoans • Others use ameboid movement to get around. • A pseudopod is extended forward, followed by the rest of the organism. http://www.youtube.com/watch?v=7pR7TNzJ_pA

14. Form & Function - Locomotion • Cilia and flagella share an internal structure of the axoneme (extending beyond the cell) consisting of 9 pairs of microtubules surrounding a central pair. • Inside the cell, the kinetosome consists of 9 triplets of microtubules just like centrioles.

15. Form & Function - Locomotion • Pseudopodia are extensions of the cell cytoplasm used for locomotion.

16. Form & Function - Locomotion • Lobopodia – large blunt extensions of the cell body. • Filopodia – are thin extensions, usually branching. • Reticulopodia – repeatedly rejoin to form a netlike mesh.

17. Form & Function - Locomotion • Axopodia – long thin pseudopodia supported by axial rods of microtubules.

18. Functional Components – Specialized Organelles • Nucleus – contains DNA. • Mitochondria – organelle used in energy production. • Golgi – part of the secretory system of the ER. • Plastids – organelles containing photosynthetic pigments. • Extrusomes – organelles that extrude something from the cell.

19. Nutrition • Holozoic feeders, or phagotrophs, ingest particles of food. • Food vacuole – the membrane-bound vesicle containing the food. • Food vacuoles fuse with lysosomes containing digestive enzymes.

20. Nutrition • Often, the site of phagocytosis is a definite mouth structure, the cytostome.

21. Nutrition • Saprozoic feeding (ingestion of soluble food) may be by pinocytosis or by transport of solutes across the cell membrane.

22. Excretion and Osmoregulation • Contractile vacuoles fill with fluid and then expel the fluid outside the cell. • Function in osmoregulation. • More common in freshwater species.

23. Reproduction • Fission is the cell multiplication process in protozoa. • Binary fission – one individual splits into two equal sized individuals. • Budding – progeny cell much smaller than parent. • Multiple fission – multiple nuclear divisions followed by multiple cytoplasmic divisions producing several offspring.

24. Reproduction • All of above accompanied by some form of mitosis. • Mitosis in protozoa divisions varies from metazoan mitosis. • Nuclear membrane often persists. • Spindle may form within the nuclear membrane. • Centrioles not observed in ciliates. • Macronucleus of ciliates elongates, constricts, and divides without mitosis (amitosis).

25. Reproduction • Many types of protists reproduce sexually as well as asexually. • Isogametes – all look alike. • Anisogametes – two different types. • Syngamy – gametes from two individuals fuse to form the zygote. • Autogamy – gametes from one individual fuse. • Conjugation – gametic nuclei are exchanged.

26. Cysts • Many protists are able to survive harsh conditions through the formation of cysts, dormant forms with resistant outer coverings and a shutdown of metabolism.

27. Major Protozoan Taxa • After the eukaryotic cell evolved, diversification followed, resulting in many clades. • Opisthokonta is a very large clade characterized by a combination of flattened mitochondrial cristae and one posterior flagellum on flagellated cells. • Includes animals, fungi, chaonoflagellates and microsporidians.

28. Stramenopila • The clade Stramenopila includes several groups of heterotrophs as well as certain groups of algae. • Most stramenopiles have a “hairy” flagellum paired with a “smooth” flagellum.

29. Stramenopila • Water molds, diatoms, golden algae, brown algae.

30. Viridiplantae • The clade Viridiplantae contains unicellular and multicellular green algae, bryophytes and vascular plants. • Phylum Chlorophyta – single celled algae colonial forms.

31. Viridiplantae • Volvox is a colonial organism that shows a division of labor where most cells are somatic cells concerned with nutrition & locomotion, but a few germ cells are responsible for reproduction. http://www.youtube.com/watch?v=9pjW1cMfTz8

32. Euglenozoa • Phylum Euglenozoa is a diverse clade that includes predatory heterotrophs, photosynthetic autotrophs, and pathogenic parasites. Kinetoplastids & Euglenids. • Persistence of nucleoli during mitosis. • Cell membrane contains microtubules to stiffen it into a pellicle.

33. Euglenids • Subphylum Euglenida have one or two flagella that emerge from a pocket at one end of the cell. • Contain chloroplasts surrounded by a double membrane – may have arisen by secondary endosymbiosis.

34. Kinetoplastids • Subphylum Kinetoplastahave a single, large mitochondrion that contains an organized mass of DNA called a kinetoplast. • Include free-living consumers of bacteria in freshwater, marine, and moist terrestrial ecosystems. • Others are parasitic. • Trypanosoma

35. Retortamonads • Phylum Retortamonada includes commensal and parasitic unicells. • Lack mitochondria & Golgi

36. Diplomonads • Phylum Retortamonada: Diplomonads: • Are adapted to anaerobic environments. • Lack plastids. • Lack mitochondria but may have mitochondrial genes in the nucleus. • Diplomonads have two nuclei and multiple flagella. • Giardia

37. Parabasalids • Parabasalids move by means of flagella and an undulating part of the plasma membrane. • This clade may have diverged from the main eukaryotic clade very early. • Trichomonas

38. Alveolata • Members of the clade (superphylum) Alveolata have membrane-bounded sacs (alveoli) just under the plasma membrane. • Dinoflagellates, apicomplexans, ciliates.

39. Alveolata - Ciliates • Members of the phylum Ciliophora use cilia to move and feed. • Ciliates have large macronuclei and small micronuclei.

40. Alveolata - Ciliates • Ciliates are a large, varied group of protists. http://www.youtube.com/watch?v=yO0tRvYEXGc&feature=player_embedded

41. Alveolata - Ciliates • Ciliates are structurally complex. • All ciliates have a kinety system made up of the cilia, kinetosomes and other fibrils. • Many have structures that can be expelled such as trichocysts and toxicysts. • Defensive function

42. Alveolata – Types of Ciliates • Suctorians – ciliates that lose cilia as adults, grow a stalk and become sessile. • Use tubelike tentacles for feeding. • Symbiotic ciliates – some commensal, others parasitic. • Free-living ciliates – may be swimmers, or sessile. • Stentor, Vorticella, Paramecium

43. Alveolata – Reproduction in Paramecium • Paramecium, as well as many other protists, reproduce asexually by binary fission.

44. Alveolata – Reproduction in Paramecium • Conjugation is a sexual process that produces genetic variation. • Conjugation is separate from reproduction which generally occurs by binary fission. http://www.youtube.com/watch?v=rgkgD4XcqTk&feature=related

45. Alveolata – Dinoflagellates • Phylum Dinoflagellata is a diverse group of aquatic photoautotrophs and heterotrophs. • Abundant in both marine and freshwater phytoplankton.

46. Alveolata – Dinoflagellates • Each has a characteristic shape that in many species is reinforced by internal plates of cellulose. • Two flagella make them spin as they move through the water.

47. Alveolata – Dinoflagellates • Rapid growth of some dinoflagellates is responsible for causing “red tides,” which can be toxic to humans. California Noctiluca Bloom http://www.whoi.edu/redtide/index.html

48. Alveolata – Dinoflagellates • Some dinoflagellates are bioluminescent. • Others live symbiotically with corals (zooxanthellae).

49. Alveolata – Apicomplexans • Apicomplexans are parasites of animals and some cause serious human diseases. • Named because one end, the apex, contains a complex of organelles specialized for penetrating host cells and tissues. • Have a non-photosynthetic plastid, the apicoplast.

50. Alveolata – Apicomplexans • Most apicomplexans have intricate life cycles with both sexual and asexual stages that often require two or more different host species for completion.