1. Eukaryotic Evolution and Diversity
Lesson 4.
Introduction to Protists

2. Learning Goals
Understand theory of endosymbiosis in the evolution of eukaryotes
Provide evidence of theory of endosymbiosis

3. Origin of Eukaryotes
First eukaryotic organism thought to have evolved about 1.5 billion years ago. Prokaryotes are as old as 4 billion years
Protozoans (protists) possibly evolved from the 1st eukaryotes by Endosymbiosis
Endosymbiosis –theory that explains how eukaryotic cells evolved from the symbiotic relationship between two or more prokaryotic cells; often one prokaryote lives inside another becoming dependent upon each other

4. Endosymbiotic Theory First postulated by Lynn Margulis in 1967
Although now accepted as a well-supported theory, both she and the theory were ridiculed by mainstream biologists for a number of years.  Thanks to her persistence, and the large volumes of data that support this hypothesis gathered by her and many other scientists over the last 30 years, biology can now offer a plausible explanation for the evolution of eukaryotes.

5. Endosymbiosis wha??? Endo = "within“
Endocytosis = (cyto = cell) a process of 'cell eating' - cells are engulfed, but then usually digested as food....
Endosymbiosis = cells are engulfed, but not digested...cells live together is a mutually benefiting relationship, or symbiosis

6. Origin of Eukaryotes
Eukaryotic cells more complex than prokaryotic cells:
Membrane-bound nucleus and organelles
Many chromosomes that occur in pairs.
Protists, fungi, plants & animals are composed of eukaryotic cells.

7. Eukaryotic Animal Cell
Typical Animal Cell

8. Eukaryotic Plant Cell
Typical Plant Cell

9. Origin of Eukaryotes Endomembrane infolding
Infolding of membrane system forming nucleus and ER

10. Origin of Eukaryotes: Cholorplasts and Mitochondria
Mitochondria and chloroplasts (endosymbionts) were prokaryotes that invaded larger cells (host cell)
Mitochondria provided energy for the host cell and chloroplasts converted solar energy into molecular energy
Endosymbiont, ancestral mitochondria:
Aerobic, heterotrophic & prokaryotic
Endosymbiont ancestral chloroplasts:
Anaerobic, autotrophic and prokaryotic

11. Origin of Eukaryotes
Ancestral chloroplasts were photosynthetic, prokaryotes that became endosymbionts (cyanobacteria)
Relationship began as parasitic or undigested prey
Assumed here that endomembrane infolding evolved first, i.e., cell already evolved nucleus, ER, …

12. Endosymbiosis HypothesisA
A prokaryote ingested some aerobic bacteria. The aerobes were protected and produced energy for the prokaryote A B C D
Cyanobacteria
Aerobic bacteria
Mitochondria
Chloroplasts N N N
Plant cell
Prokaryote N
Animal Cell

13. Endosymbiosis Hypothesis
Over a long period of time the aerobes became mitochondria, no longer able to live on their own A B C D
Cyanobacteria
Aerobic bacteria
Mitochondria
Chloroplasts N N N
Plant cell
Prokaryote N
Animal Cell

14. Endosymbiosis HypothesisC
Some primitive prokaryotes also ingested cyanobacteria, which contain photosynthetic pigments A B C D
Cyanobacteria
Aerobic bacteria
Mitochondria
Chloroplasts N N N
Plant cell
Prokaryote N
Animal Cell

15. Endosymbiosis Hypothesis
Cyanobacteria became chloroplasts, unable to live on their own A B C D
Cyanobacteria
Aerobic bacteria
Mitochondria
Chloroplasts N N N
Plant cell
Prokaryote N
Animal Cell

16. Scientific Evidence for Theory of Endosymbiosis
Membranes of chloroplasts and mitochondria are similar to those of living prokaryotes
The ribosomes found in these organelles are more similar to prokaryotic ribosomes than to ribosomes found in eukaryotes
These organelles reproduces by binary fission within the cell
Each organelle contains a circular chromosome and gene sequences match those of living prokaryotes

17. Multicellularity
Endosymbiosis does not explain multicellularity, another eukaryotic advance
First multicellular organisms existed 1.2 to 1.5 billion years ago (or half as long as unicellular organisms) Red Algae
Large complex eukaryotes fist developed 550 million years ago
Red Algae fossils

18. Life Cycles and Reproduction
Eukaryotes also have more diverse life cycles than prokaryotes
In prokaryotes cell division and reproduction are the same thing: Asexual
In multicellular eukaryotes cell division ≠ reproduction
In sexual reproduction, two individuals make eggs and sperm knows as gametes
Gametes are haploid (one set of chormosomes, ha=half) compared to cells of the rest of the organism; diploid (both sets of chromosomes, di=2)

19. Asexual Life Cycle
All prokaryotes
Some eukaryotes (yeast)

20. Gametic Sexual Life Cycle
Organism is diploid
Produces haploid gametes which are fertilized (zygote)
Zyogote undergoes mitosis (cell division) to become organism
Humans

21. Zygotic Sexual Life Cycle
Organism is haploid
Produces haploid gametes that upon fertilization form diploid zygote
Zygote undergoes meiosis to produce haploid spores that develop into organism
Most fungi
Some protists (malaria parasite

22. Sporic Sexual Life Cycle
Organism lives in 2 stages: diploid and haploid
Haploid organism produces haploid gamete
Zygote undergoes mitosis to become diploid organism
Diploid organism produces haploid spores
Haploid spores become haploid organism

23. Protists: The Unicellular Eukaryotes23

24. General Characteristics
All are eukaryotic, mostly single-celled microscopic organisms
Come in all shapes, sizes and colours
Some have cell walls, some are motile
Classified together because they do not fit into other kingdoms, rather than because they are similar or closely related to one another
Most diverse group of eukaryotes, but not as diverse as the bacteria or archaea
3 main groups of protists, characterized by how they get their nutrients. 24

25. Three groups of protists
Animal-like protists
Fungus-like protists
Plant-like protist

26. Animal-like Protists (Protozoa) – e.g. Amoebas
Consume other organisms for food
Some species are parasites

27. Protozoa Means first animals Scavengers or predators
Some are parasites.
Vary in shape and size.
Most live as single cells but others form colonies 27

28. Protozoa
Protozoa can move and are classified into four phyla based on their methods of locomotion: 28

29. Protozoa
Sarcodines: these are the amoebae, move and engulf their prey by producing pseudopodia, which are extensions of their cytoplasm. . 29

30. The Cercozoans: Phylum Cercozoa
Amoebas
Cell membrane w/o cell wall, so can change shape
Can form cytoplasmic extensions called pseudopods (false feet) for feeding and movement

31. The Ciliates: Phylum Ciliophora
Paramecia
Have many short hair-like projections called cilia (singular cilium)
move by cilia beating in a coordinated rhythm, they also help move food into the paramecium’s gullet, which leads to a food vacuole.

32. Flagellates: Phylum Zoomastigina
Have one or more flagella which whip from side to side to move them about
some are mutualistic: Trichonympha live in digestive systems of termites and help break down cellulose.
some are parasitic: Trypanosomia causes African sleeping Sickness

33. The Sporozoans: Phylum Sporozoa
Parasites
they have spores at some point in their lifecycle
they contain a number of complex organelles at one end of their bodies to help them invade their victim. Plasmodium vivax causes one type of malaria in humans

34. Life Cycle of Malaria-causing Plasmodium

35. Fungus-like Protists – e.g. Slime moulds, water moulds
Absorb nutrients from other organisms (living or dead)
Some consume other organisms, some are parasites

36. Slime and Water Moulds
Have the characteristics of fungi, protozoa and plants.
They glide from place to place and ingest food like protozoa.
They have cellulose in their cell walls like plants. They also absorb nutrients from their environment like fungi. 36

37. Plasmodial Slime Moulds (Myxomycotes)
Visible to the naked eye as tiny slug like organisms that creep over damp, decaying plant material in forests and fields.
This blob, called a plasmodium, contains many nuclei. Feed in a similar manner to amoebae. 37

38. Cellular Slime Moulds (Acrasiomycota):
exist as individual amoeboid like cells with one nucleus each.
Feed by ingesting tiny bacteria or yeast cells.
When food becomes scarce, the cells release a chemical that causes them to gather together to form a pseudoplasmodium. This is a jelly-like mass, which produces a sporangia that releases spores. 38

39. Water Moulds (Oomycota):
includes water moulds, white rusts and downy mildews
Filamentous organisms that resemble fungi. Most live as saprotrophs (dead organic matter)
some are parasitic on plants, insects and fish. They extend fungus like threads into their host where they release digestive enzymes and absorb the nutrients.
Cause of the Irish Potato Famine. 39

40. Plant-like Protists e.g. Diatoms and dinoflagellates
Make their own food by photosynthesis
Some can consume other organisms when light is unavailable

41. Diatoms: Phylum Chrysophyta
most abundant unicellular algae in the oceans. They are one of the biggest components of plankton.
Can reproduce asexually. Sexual reproduction is less common
As photosynthetic organisms they are also a major source of atmospheric oxygen. They have rigid cell walls that contain silica, a common ingredient in sand and glass.
The remains of diatoms stick around for a long time and they are used in filters, sound proofers, insulation and as a gentle abrasive in metal polishes and toothpastes. 41

42. Diatoms

43. Dinoflagellates: Phylum Pyrophyta
Unicellular, photosynthetic and mostly marine.
They have protective coats made of stiff cellulose plates. They all have two distinct flagellae
They are extremely numerous and form an important base for marine food chains. Form red tides which cause toxins to built up in shellfish that eat them. 43

44. Red Tide
Some bioluminescence

45. Euglenoids
Unicellular freshwater organisms with two flagellae, one usually much longer than the other.
They contain chloroplasts but if there is no sunlight then they lose their chloroplasts and ingest and eat food.
Have a light receptor and allows them to move towards light 45

46. Algae Simple, aquatic, plant-like organisms that contain chlorophyll
Lack the leaves, roots, stems and water-conducting materials of plants
Range in size (single cells to giant seaweeds 60 m in length)
Algae is not a proper taxonomic group
They have been on the earth for about 2 billion years and scientists are still discovering new species 46