Protists

1
Protists

• Basic traits of the protists
• Evolutionary origin and diversification of the
  eukaryotes via endosymbiosis
• Modern diversity of protists, Part 1 Diatoms,
  Brown Algae, Red Algae

2
The three domains of life
3
5 Kingdom System Monera, Protista, Plantae,
Fungi, Animalia (Robert Whittaker, 1969)
4
Figure 28.4 Protista is NOT a monophyletic
group.
Diversity in traits of protists

• Obviously, all are eukaryotes
• Varied Nutrition photoautotrophs (algae),
  ingestive heterotrophs (protozoa), absorptive
  heterotrophs (fungus-like), and mixotrophs
  (e.g., Euglena)
• Most have at least one stage that is motile (via
  flagella)
• Much variation in life cycles (pay attention to
  diploidy vs. haploidy)
• Most are found in water (damp soil, oceans,
  lakes, streams, animal bodies)

5
Figure 28.8 Euglena an example of a
singlecelled protist. The first eukaryotes were
similar single-celled ancestors of the protists.
How did the first eukaryote evolve from a
prokaryote ancestor?
6
Protists

• Basic traits of the protists
• Evolutionary origin and diversification of the
  eukaryotes via endosymbiosis
• Modern diversity of protists, Part 1 Euglenoids,
  Water Molds, and Slime Molds

7
Some major episodes in the history of life
8
Figure 26.10 Clock analogy for some key events
in Earths history
Prokaryotes set the stage by Origin of life 3.7
mya Evolution of photosynthesis Generation of
oxygen in atmosphere Ability to utilize oxygen
in respiration
9
Remember two key traits of Eukrayotes

• DNA organized into a nucleus, surrounded by a
  membrane
• Membrane-bound organelles (mitochondria and
  sometimes chloroplasts)

10
Figure 26.13 A model of the origin of eukaryotes
from prokaryotes plasma membrane infolding and
specialization, followed by serial
endosymbiosis.
cyanobacterium
11
Evidence supporting the serial endosymbiosis
theory

• Existence of endosymbioses today
• Similarity between bacteria and
  mitochondria/chlorplasts
• Similar size
• inner membrane enzymes transport systems
• replication by binary fission
• circular DNA molecule, with similar sequences
• similar ribosomes
• plastids have double (or more) membranes

12
An earlier hypothesis for how the three domains
of life are related
13
A recent alternative hypothesis for how the three
domains of life are related

• All three domains have DNA that was transferred
  from other domains
• No single common ancestor. Ancestor was a
  community of cells that swapped DNA many times

14
Some major episodes in the history of life. Note
the evolution of the eukaryotic cell resulted in
a burst of evolutionary diversification on earth.
Why did this happen?
15
Eukaryotic cell advantages

• Larger and more complex
• Greater capacity to specialize, adapt
• Thus could take advantage of a wider range of
  conditions

16
Protists

• Basic traits of the protists
• Evolutionary origin and diversification of the
  eukaryotes via endosymbiosis
• Modern diversity of protists, Part 1 Diatoms,
  Brown Algae, Red Algae

17
Figure 28.4 A tentative phylogeny of eukaryotes.
18
Figure 28.4 A tentative phylogeny of eukaryotes.
19
Figure 28.4 A tentative phylogeny of eukaryotes.
20
Figure 28.13 Stramenopila hairy flagellum.
Sometimes these flagella are found only on the
motile gametes.
21
Figure 28.4 A tentative phylogeny of eukaryotes.
Alga photosynthetic protist
22
Table 27.1 Classifying organisms by how they
obtain carbon (to build cells and organic
molecules) and energy (to power metabolism and
molecular construction).
23
Figure 54.2 An overview of ecosystem
dynamicsand trophic ecology. Note blue arrows
represent material cycling and broken red arrows
represent energy flow.
24
Figure 28.4 A tentative phylogeny of eukaryotes.
Alga photosynthetic protist
Heterokont algae are the algae in Stramenopila
(browns, goldens, and diatoms)
25
Figure 28.4 A tentative phylogeny of eukaryotes.
Alga photosynthetic protist
Heterokont algae are the algae in Stramenopila
(browns, goldens, and diatoms)
The plastids of the heterokont algae evolved by
secondary endosymbiosis, and thus have triple
membranes.
26
Figure 28.3 A model for the evolution of algal
diversity, especially diversity in plasmids
secondary endosymbiosis. Notice each
endosymbiotic event adds a membrane layer to the
engulfed plastid.
27
Figure 28.3 A model for the evolution of algal
diversity, especially diversity in plasmids
secondary endosymbiosis. Notice each
endosymbiotic event adds a membrane layer to the
engulfed plastid.
Or two.
28
Figure 28.3 A model for the evolution of algal
diversity, especially diversity in plasmids
secondary endosymbiosis. Notice each
endosymbiotic event adds a membrane layer to the
engulfed plastid.
One outer membrane.
29
Figure 28.3 A model for the evolution of algal
diversity, especially diversity in plasmids
secondary endosymbiosis. Notice each
endosymbiotic event adds a membrane layer to the
engulfed plastid.
Double membrane.
30
Figure 28.3 A model for the evolution of algal
diversity, especially diversity in plasmids
secondary endosymbiosis. Notice each
endosymbiotic event adds a membrane layer to the
engulfed plastid.
Triple or quadruple membrane.
31
Figure 28.4 A tentative phylogeny of eukaryotes.
Alga photosynthetic protist
Heterokont algae are the algae in Stramenopila
(browns, goldens, and diatoms)
The plastids of the heterokont algae evolved by
secondary endosymbiosis, and thus have triple
membranes.
The colors of algae are due to accessory pigments
in their plastids
32
Figure 28.4 A tentative phylogeny of eukaryotes.
33
Figure 28.16 Diatoms (Phylum Bacillariophyta)
one of the heterokont algae. Diatoms have unique
glass-like cell walls made of silica. They are
VERY abundant as plankton in the surface waters
of lakes, rivers, and oceans. They reproduce
sexually only rarely.
34
Figure 28.15 Diatom shell. Note diatoms have a
two-part cell wall, one of which fits inside the
other like the parts of a shoe box.
35
Diatom Life Cycle 1.Usually Asexual Reproduction
2n
2n
2n
2n
mitosis
mitosis
2n
2n
mitosis
2n
36
Diatom Life Cycle 2.Occasional Sexual
Reproduction
n
meiosis
2n
2n
n
fertilization
37
When diatoms do reproduce sexually, their life
cycle is like an animals, except never
multicellular
(and some algae, like diatoms)
38
Diatomaceous Earth
39
pennate vs. centric shapes
bilateral symmetry
40
pennate vs. centric shapes
radial symmetry
41
Diatoms

• Photoautotrophs
• Make up phytoplankton in oceans, lakes, streams
• Silica cell walls
• Primarily asexual reproduction, diploid

42
Figure 28.4 A tentative phylogeny of eukaryotes.
43
Figure 28.18 Brown algae (Phaeophyta) another
heterokont alga. Brown algae are the largest and
most complex algae. All are multicellular, and
most are marine (i.e., oceanic). Many exist as
seaweeds (large oceanic algae) in cool ocean
waters.
44
Floats (air-filled bladders) on Sargassum
Sargassum are hugely abundant in the Sargasso Sea
45
Sieve tubes in kelps are analogous to phloem in
plants.
Would kelp have something analogous to xylem?
46
Kelp forest (made up of very large brown algae).
47
Figure 28.21 The life cycle of Laminaria an
example of alternation of generations
Many of the large multicellular algae (kelps),
including many brown, red, and green algae,
exhibit this kind of life cycle, which is like
the life cycle of plants.
Laminaria are heteromorphic - the gametophyte and
sporophyte differ in appearance. Other alga can
be isomorphic - both the haploid and diploid
forms look the same.
48
Figure 13.6 The three main types of sexual life
cycles, differing in the timing of meiosis and
fertilization.
49
Brown algae

• Photoautotrophs
• Primarily in cool ocean waters
• Alternation of generations
• Kelp provide both energy/food and structure to
  kelp forest ecosystems

50
Figure 28.4 A tentative phylogeny of eukaryotes.
51
Figure 28.4 A tentative phylogeny of eukaryotes.
Red algae have chloroplasts with a double
membrane.
52
Figure 28.3 A model for the evolution of algal
diversity, especially diversity in plasmids
secondary endosymbiosis. Notice each
endosymbiotic event adds a membrane layer to the
engulfed plastid.
Double membrane.
53
Figure 28.4 A tentative phylogeny of eukaryotes.
Red algae have chloroplasts with a double
membrane.
Primary endosymbiosis only.
(Like green algae, plants)
54
Figure 28.28 Red algae (Rhodophyta) unique
algae, closely related to the Green algae. Do
not have flagellated stages. Plastids evolved
by primary endosymbiosis of cyanobacteria.
Dominant large algae in warm ocean waters, though
also found abundantly in cool ocean waters.
Diverse life cycles, but many exhibit
alternation of generations.
55
Red algae

• Primarily found in warm ocean waters
• May have alternation of generations
• Chloroplasts have double membranes

56
Figure 28.20 Brown and red algae provide food
and other useful materials.
Gel-forming substances In cell walls algin in
brown algae agar and carrageenan In red algae