Chapter 28

Chapter 28: Protists

Protists are eukaryotes not classified as plants, animals, or fungi.

Found in moist habitats and mostly microscopic.

Classified by ecological roles:

Algae- Photoautotrophs (photosynthetic).

Protozoa- Heterotrophs (animal-like).

Fungus-like protists- Absorptive nutrition.

Classified by habitat:

Commonly found in oceans, lakes, wetlands, and rivers

Plankton- swimming or floating protists, bacteria, viruses, and small animals

Phytoplankton- photosynthetic protists

Periphyton- attached by mucilage to underwater surfaces (seaweeds or macroalgae)

Classified by motility:

Flagellates- swims using flagella 

- Cryptomonads- unicellular flagellates 

Cilia (Ciliates)

Amoeboid movement (Amoebae with pseudopodia)

- Gliding using slime.

Supergroup Excavata

Unicellular flagellates often characterized by feeding grooves 

Eugelnoids

- Some are heterotrophic, but Euglena is photosynthetic 

Kinetoplastids 

- Characterized by large mass of DNA, kinetoplast

Metamonds 

- Some are parasites

- Highly modified mitochondria 

Supergroup of plants and relatives 

Derive from cyanobacteria, plastids have two envelope membrane 

Kingdom Plantae (land plants)

Phylum Chlorophyta (green algae)

- Occurs in freshwater, ocean, and on land 

- Most are photosynthetic 

Phylum Rhodophyta (red algae)

- Red due to distinctive photosynthetic pigments 

Supergroup Alveolata

Named for saclike membranous vesicles (alveoli) present 

Ciliophora (Ciliates- conjugation)

Apicomplexa (medically important parasites)

Dinozoa

- Dinoflagellates (produces toxins)- half contain photosynthetic plastids and half are heterotrophic 

- Secondary plastids derived from red algae and some from green algae 

Supergroup Stramenopila

Algae, protozoa, and fungus-like protists

Straw like flagellar hair 

Produce flagellate cells 

Heterotrophic or photosynthetic 

Supergroup Rhizaria

Have thin, hairlike extensions of cytoplasm called filose pseudopodia 

Phylum Chlorarachniophyta

Phylum Radiolaria

Phylum Foraminifera  

Secondary plastids when present derive from endosymbiotic green algae 

Supergroup Amoebozoa 

Model for understanding movement, cell communication, and development 

Amoeboid movement by pseudopodia 

Supergroup Opisthokonta

Animals and fungal kingdoms and related protists 

Swimming cells possess a single posterior flagellum

Endosymbiosis and Evolution

Endosymbiosis- lives inside the body of their host  

Primary plastids 

- Evolved via cyanobacteria engulfment.

- Resulted in horizontal gene transfer 

- Originate from primary endosymbiosis 

Secondary plastids 

- Arise from photosynthetic eukaryotes engulfed by other cells.

- Originate from secondary endosymbiosis 

Tertiary plastids 

- Obtained by tertiary endosymbiosis (acquisition by host of plastids from cells that already have secondary plastids)

Nutritional and Defensive Adaptations 

Phagotropgy- heterotrophs that ingest particles 

Osmotrophy- heterotrophs that rely on uptake of small organic molecules

Photoautotrophy- photosynthetic 

Mixotrophy- autotrophy and phagotrophy or osmotrophy depending on conditions 

Extrusomes- spear-shaped projectiles discourage herbivores 

Bioluminescence- startles herbivores 

Toxins (Dinoflagellates)- inhibit animal physiology

Slimy Mucilage or cell walls defend against herbivores and pathogens 

Reproductive Adaptations

Asexual reproduction (e.g., cysts in harsh conditions).

Sexual reproduction

- Gametes and zygotes 

Haploid dominant life cycles (look over figure 28.25)

- Most unicellular sexually reproducing protists

- Haploid cells develop into gametes 

Alteration of Generations 

- Haploid gametophyte produces gametes 

- Diploid sporophyte produces spores by meiosis

Diploid-Dominant Life Cycles 

- All cells except gametes are diploid

- Gametes are produced by meiosis

- Diatoms

Parasitic Protist Life Cycle

-Use more than one host organism.