Figure 27.2 The three domains of life
“Protists”
1) Basic traits of the protists
2) Evolutionary origin and diversification
of the eukaryotes via endosymbiosis
3) Modern diversity of protists, Part 1:
Plant-like protists
Figure 26.1 Some major episodes in the history of life
Figure 28.2 “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)
“Protists”
Figure 28.4 A model of the origin of eukaryotes from prokaryotes: plasma
membrane infolding and specialization, followed by “serial endosymbiosis.”
Step 1
(Step 3)
1) Basic traits of the protists
2) Evolutionary origin and diversification
of the eukaryotes via endosymbiosis
3) Modern diversity of protists, Part 1:
Euglenoids, Water Molds, and Slime
Molds
Step 2
Evidence supporting the serial
endosymbiosis theory
Figure 28.5 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.
• 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
Figure 28.6 An earlier hypothesis for how the three domains of life are related
Figure 28.7 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
Figure 26.1 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?
“Protists”
1) Basic traits of the protists
2) Evolutionary origin and diversification of
the eukaryotes via endosymbiosis
3) Modern diversity of protists, Part 1:
Euglenoids, Water Molds, and Slime
Molds
Figure 28.8 A tentative phylogeny of eukaryotes.
Figure 28.4 A tentative phylogeny of eukaryotes.
Figure 28.4 A tentative phylogeny of eukaryotes.
Figure 28.3 Euglena: an example of a single–celled protist. The first
eukaryotes were similar single-celled ancestors of the protists. How did the
first eukaryote evolve from a prokaryote ancestor?
Key features of Euglenids
•
•
•
•
•
•
Eye spot, light detector, phototaxis
Unicellular
Motile
Mixotrophy
Asexual reproduction only
No cell walls (protein bands for strength)
Mixotrophy
• Euglena have chloroplasts and carry out
photosynthesis, acquiring energy from
sunlight (autotrophic)
Table 27.1 Classifying organisms by how they obtain carbon (to build cells and
organic molecules) and energy (to power metabolism and molecular
construction).
Mixotrophy
Figure 54.2 An overview of ecosystem dynamics
and trophic ecology. Note: blue arrows represent material cycling and broken
red arrows represent energy flow.
Table 27.1 Classifying organisms by how they obtain carbon (to build cells and
organic molecules) and energy (to power metabolism and molecular
construction).
• Euglena have chloroplasts and carry out
photosynthesis, acquiring energy from
sunlight (autotrophic)
• When light availability is inadequate,
Euglena can absorb organic nutrients from
the environment or engulf prey
(heterotrophic)
Figure 54.2 An overview of ecosystem dynamics
and trophic ecology. Note: blue arrows represent material cycling and broken
red arrows represent energy flow.
Mixotrophy
• Euglena have chloroplasts and carry out
photosynthesis, acquiring energy from
sunlight (autotrophic)
• When light availability is inadequate,
Euglena can absorb organic nutrients from
the environment or engulf prey
(heterotrophic)
• This ability to switch between autotrophy
and heterotrophy is called mixotrophy
Figure 28.4 A tentative phylogeny of eukaryotes.
Note that the
water molds are
more closely related
to the brown algae
than they are to
the slime molds.
(Or to the Fungi for
that matter.)
Protist Diversity
• The golden browns: Chrysophyta
• The Dinoflagellates: Dinophyta
• The Diatoms: Bacillariophyta
•
•
•
•
Evolutionary notes
General Characteristics
Reproduction
Ecology/human impact
Figure 28.4 A tentative phylogeny of eukaryotes.
Golden Algae: Chrysophyta
• Photosynthetic
• Chlkorophyll a & c and
carotenoids
• Biflagellated
• Autotrophs or mixotrophs
• Can form cysts
• Unicellular or colonial
Figure 28.25 A hypothetical history of plastids in the photosynthetic
eukaryotes
Dinoflagellates
• Mostly phosynthetic autotrophs, some are
heterotrophic
• Unicellular
• 2 flagella (many)
• Chlorophyll a & c, carotenoids
• Cellulose cell wall
• Many are bioluminescent
• Some are mutualistic symbionts in marine
invertebrates
• Some species are responsible for red tides
(toxins)
Figure 28.8 A tentative phylogeny of eukaryotes.
Stramenopila = hairy
flagellum
Sexual (2N)
Alga = photosynthetic
protist
Asexual
(binary fission)
1N
“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
Figure 28.17 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.
Diatoms: Bacillariophyta
• Photoautotrophs
• Solitary or colonial
• Make up phytoplankton in oceans, lakes,
streams - extremely important contributors
to global Oxygen!
• Silica cell walls
• Primarily asexual reproduction, diploid some sexual reproduction
• Form auxospores - resting stage
• Chlorophyll a and c and fucoxanthin (a
carotenoid)
Diatom Life Cycle
asexual Reproduction
A diatom frustule
They get smaller with successive generations!