Chapter 24 - Protists

Eukaryotes

• Differences from prokaryotes

  • Cytoskeleton

  • Compartmentalization including nuclear envelope and organelles

• May have appeared about 2.7 BYA based on chemical evidence

• Microfossils of a new type of organisms seen about 1.5 BYA

• Eukaryotic cells evolved from relationships with prokaryotic organisms

Theory of Endosymbiosis

• Endosymbiotic relationships between prokaryotic organisms led to the development of eukaryotic cells

• Nucleus and ER

  • Evolved through infoldings of outer membranes

• Mitochondria

  • Formed from larger bacteria engulfing energy-producing bacteria

• Chloroplasts

  • Evolved from engulfed photosynthetic organisms

Protists

• Most ancient of the eukaryotes

• Exhibit massive diversity

• Classified based on what they are not, do not fit into other eukaryote kingdoms

• Most are found in aquatic environments, some may be parasitic or asociated with dead organisms

Locomotion

• Cilia

  • Create water currents

• Flagella

  • Many have one or more they wave to move

• Pseudopodia

  • “False feet” extensions of the cell body used by amorbos, can also be used to capture food

    Nutrition (energy)

• Autotrophic

  • Photosynthetic or chemoautotrophic

• Heterotrophic

  • Organic molecules from other organisms

  • Phagotrophs

    • Ingest food particles into food vacuoles

• Mixotrophs

  • Both heterotrophic and phototrophic

Sizes of Protists

• Unicellular

  • Microscopic

• Colonies

  • Collection of cells permanently associated but with little integration of cell activities

• Multicellular

  • Composed of individual cells that have coordinated activities

  • Include 3 phyla of algae

Reproduction

• Asexual

  • Mitosis (with differences), binary or multiple fission, budding

• Sexual

  • Produce gametes using meiosis, some like paramecium use conjugation to exchange the gametes

• Cysts

  • Dormant form of a cell with a resistant outer covering, form when conditions are harsh

• All reproduce asexually

• Binary fission

  • Divides into 2 identical individuals (clones)

• Rapid reproductive rate

• Some reproduce sexually

  • Conjugation

    • Opposite mating strands pair and exchange genetic material (DNA)

Protist

• Around 200,000 distantly related organisms in 15 plyla

• Now use molecular systematics to group into 5 supergroups

Excavata

• Named for groove on one side of the cell body in some forms

• Unicellular, heterotrophic, flagellates

• 3 major clades

  • Diplomonads and Parabasalids

    • Modified mitochondria

  • Euglenozoa

    • Structurally unique flagella, some have chloroplasts

Euglena

• Can change shape

• Mitochondria

• Stigma to move towards the light

• Contain chloroplasts, but can also be heterotrophs and use phagocytosis

SAR

• 3 groups, have chloroplasts

• Stramenopiles

  • Brown Algae (seaweed)

    • Common in northern regions, transport of nutrients can be hard

  • Diatoms

    • Photosynthetic organisms, have 2-part shells

  • Alveolata

    • Have flattened vesicles called alveoli

• Contain 3 subgroups including the:

  • Dinoflagellates

    • Photosynthetic, cause red tides

  • Paramecium

    • Heterotrophs with cilia

    • Use mitosis and conjugation to reproduce

  • Rhizaria

    • Have silicon exoskeleton or limestone shells

    • Many have amorphous shapes with pseudopods to capture food

    • Some are symbiotic

    • Includes the radiolarians

Archaeplastida

• Believed to have descended from a single endosymbiotic event over 1 BY

• Includes the:

  • Rhodophyte

    • Found in tropical costal waters, vary in size and form, have commercial uses

  • Chlorophyte

    • Extensive fossil record, plants evolved from these

Amoebozoa

• Use pseudopods to move and capture food

• Include plasmodial and cellular slime molds

• Once considered fungi

Opisthokonta

• The Choanoflagellates

• Closet relatives to animals, similar to sponges