Eukaryotic Evolution and Diversity

1
Eukaryotic Evolution and Diversity

• Lesson 4.

Introduction to Protists
2
Learning Goals

• Understand theory of endosymbiosis in the
  evolution of eukaryotes
• Provide evidence for the theory of endosymbiosis
• Distinguish between the 3 groups of protists
  (animal fungus plant-like)

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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

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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.

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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 in a mutually
  benefiting relationship, or symbiosis

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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.

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Typical Animal Cell
Eukaryotic Animal Cell
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Typical Plant Cell
Eukaryotic Plant Cell
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Origin of Eukaryotes Endomembrane infolding
Infolding of membrane system forming nucleus and
ER
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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

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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,

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Endosymbiosis Hypothesis
A
A prokaryote ingested some aerobic bacteria. The
aerobes were protected and produced energy for
the prokaryote
A
B
C
D
Cyanobacteria
Aerobic bacteria
Chloroplasts
Mitochondria
N
N
Plant cell
Prokaryote
N
Animal Cell
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Endosymbiosis Hypothesis
B
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
Chloroplasts
Mitochondria
N
N
Plant cell
Prokaryote
N
Animal Cell
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Endosymbiosis Hypothesis
C
Some primitive prokaryotes also ingested
cyanobacteria, which contain photosynthetic
pigments
A
B
C
D
Cyanobacteria
Aerobic bacteria
Chloroplasts
Mitochondria
N
N
Plant cell
Prokaryote
N
Animal Cell
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Endosymbiosis Hypothesis
D
Cyanobacteria became chloroplasts, unable to live
on their own
A
B
C
D
Cyanobacteria
Aerobic bacteria
Chloroplasts
Mitochondria
N
N
Plant cell
Prokaryote
N
Animal Cell
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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

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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
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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,
  hahalf) compared to cells of the rest of the
  organism diploid (both sets of chromosomes,
  di2)

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Asexual Life Cycle

• All prokaryotes
• Some eukaryotes (yeast)

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Gametic Sexual Life Cycle

• Organism is diploid
• Produces haploid gametes which are fertilized
  (zygote)
• Zyogote undergoes mitosis (cell division) to
  become organism
• Humans

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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

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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

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Protists The Unicellular Eukaryotes
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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.

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Three groups of protists

• Animal-like protists
• Fungus-like protists
• Plant-like protist

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Animal-like Protists

• (Protozoa) e.g. Amoebas
• Consume other organisms for food
• Some species are parasites

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Protozoa

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

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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
• http//www.youtube.com/watch?v7pR7TNzJ_pA

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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 parameciums
  gullet, which leads to a food vacuole.
• http//www.youtube.com/watch?vfh_yjLppNAgfeature
  fvwrel

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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
• http//www.youtube.com/watch?v9duvzqvVflw

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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

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Life Cycle of Malaria-causing Plasmodium

• http//highered.mcgraw-hill.com/olc/dl/120090/bio4
  4.swf

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Fungus-like Protists

• e.g. Slime moulds, water moulds
• Absorb nutrients from other organisms (living or
  dead)
• Some consume other organisms, some are parasites

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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.

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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.
• http//www.youtube.com/watch?vkhEAZabMtOkfeature
  related

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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.

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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.

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Plant-like Protists

• e.g. Diatoms and dinoflagellates
• Make their own food by photosynthesis
• Some can consume other organisms when light is
  unavailable

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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.

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Diatoms
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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.

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Red Tide
Some bioluminescence http//www.youtube.com/watch?
vPy-J1ZazHDMfeaturefvwrel
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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

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Homework

• Pg 69, Q 13-18
• Pg 76, Q 19-24