“Protists”

1) Basic traits of the protists

2) Evolutionary origin and diversificationof the eukaryotes via endosymbiosis

3) Modern diversity of protists, Part 1:Plant-like protists

Figure 27.2 The three domains of life

Figure 26.1 Some major episodes in the history of life Figure 28.2 “Protista” is NOT a monophyletic group.

• Obviously, all areeukaryotes

• Varied Nutrition:photoautotrophs (“algae”),ingestive heterotrophs(“protozoa”), absorptiveheterotrophs (fungus-like),and “mixotrophs” (e.g.,Euglena)

• Most have at least one stagethat 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)

Diversity in traits of protists:

“Protists”

1) Basic traits of the protists

2) Evolutionary origin and diversificationof the eukaryotes via endosymbiosis

3) Modern diversity of protists, Part 1:Euglenoids, Water Molds, and SlimeMolds

Figure 28.4 A model of the origin of eukaryotes from prokaryotes: plasmamembrane infolding and specialization, followed by “serial endosymbiosis.”

Step 1

Step 2

(Step 3)

Evidence supporting the serialendosymbiosis 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

Figure 28.5 A model for the evolution of algal diversity, especially diversity inplasmids: secondary endosymbiosis. Notice: each endosymbiotic event addsa membrane layer to the engulfed plastid.

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 threedomains of life are related

• All three domainshave DNA that wastransferred fromother domains

• No single commonancestor. Ancestorwas a community ofcells that swappedDNA many times

Figure 26.1 Some major episodes in the history of life. Note: the evolution ofthe 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 ofthe eukaryotes via endosymbiosis

3) Modern diversity of protists, Part 1:Euglenoids, Water Molds, and SlimeMolds

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 firsteukaryotes were similar single-celled ancestors of the protists. How did thefirst 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 outphotosynthesis, acquiring energy fromsunlight (autotrophic)

Table 27.1 Classifying organisms by how they obtain carbon (to build cells andorganic molecules) and energy (to power metabolism and molecularconstruction).

Figure 54.2 An overview of ecosystem dynamicsand trophic ecology. Note: blue arrows represent material cycling and brokenred arrows represent energy flow.

Mixotrophy

• Euglena have chloroplasts and carry outphotosynthesis, acquiring energy fromsunlight (autotrophic)

• When light availability is inadequate,Euglena can absorb organic nutrients fromthe environment or engulf prey(heterotrophic)

Table 27.1 Classifying organisms by how they obtain carbon (to build cells andorganic molecules) and energy (to power metabolism and molecularconstruction).

Figure 54.2 An overview of ecosystem dynamicsand trophic ecology. Note: blue arrows represent material cycling and brokenred arrows represent energy flow. Mixotrophy

• Euglena have chloroplasts and carry outphotosynthesis, acquiring energy fromsunlight (autotrophic)

• When light availability is inadequate,Euglena can absorb organic nutrients fromthe environment or engulf prey(heterotrophic)

• This ability to switch between autotrophyand heterotrophy is called mixotrophy

Figure 28.4 A tentative phylogeny of eukaryotes.

Note that the water molds aremore closely related to the brown algae than they are tothe slime molds.

(Or to the Fungi forthat 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 photosyntheticeukaryotes

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)

Sexual (2N)

Asexual(binary fission)1N

Figure 28.8 A tentative phylogeny of eukaryotes.

Alga = photosyntheticprotist

“Heterokont” algae arethe algae inStramenopila (browns,goldens, and diatoms)

The plastids of theheterokont algaeevolved by secondaryendosymbiosis, andthus have triplemembranes.

Stramenopila = hairyflagellum

The colors of algae aredue to accessorypigments 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 VERYabundant 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 contributorsto 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 Cycleasexual Reproduction

A diatom frustule

They get smaller with successive generations!