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“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

Lectures on Protists •  Generalizations about protist ecology •  For each group, pay attention to:

– Mode of nutrition – Life cycle – Distinguishing characteristics

•  Serial endosymbiosis, primary vs. seconday endosymbiosis

•  Eukaryotic Cell Advantages •  Know how the different groups we study

are related

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 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)

Diversity in traits of protists: “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

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Evidence supporting the serial endosymbiosis theory

•  Existence of endosymbioses today (wolbachia)

•  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 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: Plant-like protists

Figure 28.8 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) •  Chlorophyll a and b and carotenoids

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Figure 28.25 A hypothetical history of plastids in the photosynthetic eukaryotes Table 27.1 Classifying organisms by how they obtain carbon (to build cells and

organic molecules) and energy (to power metabolism and molecular construction).

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

•  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

Protist Diversity cont.

•  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.

How many membranes do you think the golden algae’s chlorplasts have?

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Golden Algae: Chrysophyta •  Photosynthetic •  Chlorophyll a & c and

carotenoids (Fucoxanthin) •  Biflagellated •  Autotrophs or mixotrophs •  Can form cysts •  Unicellular or colonial •  Mostly fresh water •  Cellulose or silica cell walls

Figure 28.9 Alveolates are characterized by membrane-bound sacs (alveoli) beneath the plasma membrane.

Figure 28.10 Dinoflagellates spin due to the beating of a pair of spiral flagella lying in a groove encircling the cell.

Dinoflagellates (Dinophyta) •  Mostly phosynthetic autotrophs, some are

heterotrophic •  Unicellular •  2 flagella (many) •  Chlorophyll a & c, carotenoids (peridinin) •  Cellulose cell wall (or none) •  Many are bioluminescent •  Some are mutualistic symbionts in marine

invertebrates •  Some species are responsible for red tides

(toxins)

Sexual (2N)

Asexual (binary fission) 1N

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Zooxanthellae - keys to coral reef productivity Figure 32.1 A coral reef. Corals are colonial animals, with photsynthetic dinoflagellate symbionts.

Figure 28.8 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.

Stramenopila = hairy flagellum

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)

Figure 28.17x Diatom shell. Note: diatoms have a two-part cell wall, one of which fits inside the other like the parts of a shoe box.

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pennate vs. centric shapes Diatom Life Cycle asexual Reproduction

A diatom frustule

They get smaller with successive generations!

Diatom Life Cycle 2. Occasional Sexual Reproduction

2n

meiosis

n

n

Oogamous in centric diatoms

Isogamous in pennate (with no flagellated male gametes)

Diatom Life Cycle 2. Occasional Sexual Reproduction

2n

meiosis

n

n

fertilization 2n

When diatoms do reproduce sexually, their life cycle is like an animal’s, except never multicellular

(and some algae, like diatoms)