Ch.28 eukaryotic diversity

The Origins of Eukaryotic Diversity

Chapter 28

Protists

• 1st eukaryotes

• Protists lived 2 billion years before the evolution of plants, fungi & animals

• Most diverse group of eukaryotes

• Live anywhere there is water

• Protists could include as many as 20 kingdoms

Definition of Protists

• Mostly single-cellular

• Some colonial and multicellular

• Eukaryotic

Protist Nutrition

• Aerobic, use mitochrondria

• Can be– Photoautotrophs (algae)– Heterotrophs (protozoa)– Mixotrophs

Protist Motility

• Cilia or flagella– Most have one at some point in life– 9+2 arrangement of microtubules

Trends toward the evolution of eukaryotes

• Multicellular prokaryotes

• Prokaryotic communities

• Compartmentalization of functions within cell

Serial Endosymbiosis

Secondary Endosymbiosis

A hypothetical history of plastids in the photosynthetic eukaryotes

Traditional hypothesis for how the three domains of life are related

An alternative hypothesis for how the three domains of life are related

The kingdom Protista problem

A tentative phylogeny of eukaryotes

Evolution of Multicellularity

• Eukaryotes– Organization allowed for development of more

complex structures– Opportunities to specialize & adapt

• Multicellularity evolved several times– Multicellular algae (seaweeds)– Ancestors of plants, fungi & animals

Survey of Protistan Diversity

Diplomonadida & Parabasala

• Lack mitochondria

Giardia lamblia Trichomonas vaginalis

Euglenazoa

• Photosynthetic & heterotrophic flagellates

Alveolata:unicellular protists w/ subcellular cavities

• Dinoflagellates


• Apicomplexans


• Ciliates

Ciliates: Stentor (left), Paramecium (right)

Conjugation and genetic recombination in Paramecium caudatum

Stramenopila:Water molds & Heterokont algae

“hairy” flagella

• Oomycota (water molds)– Resemble fungi (but not closely related)– Cell walls made of cellulose– Diploid life cycle

The life cycle of a water mold

• Heterokont algae– 3-membraned plastids

– Types• Diatoms• Golden algae• Brown algae



• Diatoms– Box-like silica walls– Freshwater & marine plankton



• Golden algae

• (Chrysophyta)– Yellow and brown

pigments • (carotene and

xanthophyll)

– Can form resistant cysts



• Brown algae (Phaeophyta)– Largest & most complex algae– Brown pigments



Alternation of Generations

Rhodophyta: Red Algae

• Lack flagella

• Phycoerythrin – red pigment (a phycobilin)

• Can absorb light in deep water

• Most are marine

Chlorophyta: Green Algae• Share common ancestor with plants• Most are freshwater• Unicellular, colonial & multicellular species• Some are seaweeds• Form lichens

Protists that Use Pseudopodia

• Rhizopods (amoebas)– Move and feed w/ psuedopodia

• Actinopods – Axopodia help cell float and feed by phagocytosis

• Foraminferans – Porous, calcareous shells– Cytoplasmic strands extend through pores and

function in swimming, shell formation & feeding

Use of pseudopodia for feeding: Amoeba

Actinopods: Heliozoan (left), radiolarian (right)

Foraminiferan

Mycetozoa: Slime Molds

• Resemble fungi b/c of convergent evolution (not actually related)

• Plasmodial slime molds– Heterotrophic– Grow on rotting plant material– Feeding stage is called a plasmodium

• Multinucleate amoeboid mass

• Cellular slime molds– Feeding stage: haploid amoeboid cells– In absence of food: form a slug-like mass

Plasmodial slime mold

Figure 28.29 The life cycle of a plasmodial slime mold, such as Physarum

The life cycle of a cellular slime mold (Dictyostelium)

Ch.28 eukaryotic diversity

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