C2.4 - Kingdom Protista and Eukaryotes

Background

• protist: eukaryote that isn’t a plant, animal, or fungi
• Appear early in fossil record
• All eukaryotes
• Most microscopic and unicellular
• Three main groups
  • Plant-like protists
  • Animal-like protists
  • Fungi-like protists
• Kingdom of convenience
  • Can’t group them? Put them in protist kingdom

Structure and Function

• protists have diverse structures and functions
• found in many habitats including oceans, soil, snow, and even air
• most are unicellular and free-living
• some are colonial or multicellular like kelp
• multicellular protists have specialized cells
• protists have eukaryotic cell structures with nucleus and organelles
• eukaryotic structure is shared by all non-bacteria and non-archaea
• cell structure alone does not define protists
• traditional protist kingdom may be split into several kingdoms
• nucleic acid comparisons help identify evolutionary branches
• evidence of protist evolution is still incomplete
• term protist remains useful despite classification debates
• protists likely evolved from ancient prokaryotes
• plants, animals, and fungi evolved from protists

Origin of Eukaryotes

• “theory,” not proven
• eukaryotic cells evolved from combination of
  • infolding
  • serial endosymbiosis
• Infolding
  • plasma membrane fold inwards
  • formed
    • endoplasmic reticulum (ER)
    • Golgi apparatus
    • nuclear envelope
• serial endosymbiosis
  • prokaryotes engulfed by host cell
  • prokaryotes are not digested
  • over time, they evolve and form symbiotic relationship w/ host cell
  • perform cell’s metabolic tasks

Origins of eukaryotes

Motility

• pseudopodia: streaming cytoplasm into cellular extensions
  • i.e. amoebas
  • pseudopods (false feet)
• flagella: long hair-like projections extending out of cell membrane
• cilia: shorter hair-like projections that cover entire cell membrane or large clusters
• zooflagellates: heterotrophic protists w/ flagella
• ciliates: protists w/ cilia
• spores: reproductive cells released by organisms
  • often found in protists relying on passive modes of transportation

Analogy of flagella vs. cilia

Plant-like Protists

• algae: plant-like protists
• can undergo population explosions producing harmful algae blooms
• many unicellular, some live in colonies, others are multicellular
• Contain chlorophyll for photosynthesis
• “chloro” = Greek for green
• Mostly multicellular but w/o tissues
• Found in aquatic or damp environments
• Group consists of 4 divisions

Other Classifications (textbook)

• classified by differences in
  • cell walls
  • types of photosynthetic pigments
  • structure
  • types of storage carbohydrates
  • sequences of nucleic acids
• dinoflagellates: unicellular protists w/ cell wall made of cellulose and 2 flagella
• plankton: communities of mostly microscopic organisms that drift / swim near surface of ponds, lakes, and oceans

Division Chlorophyta (Green “Plant”)

• Green algaes
• phytoplankton: unicellular photosynthetic green algae
• Primary producers in aquatic environments
• Supplies 67% of global oxygen supply

Division Phaeophyta

• Brown algaes
• Sea weeds
• Most crude oil derived from brown algae that lived mil. of yrs. ago

Division Rhodophyta

• Red algaes
• Sea weeds
• Sources of agar used in:
  • drug capsules
  • gels
  • cosmetics
  • ice cream
  • toothpaste
• Eaten as nori and dulce

Division Chrysophyta

• Golden algae and diatoms
• Diatoms produce silica (sand) shells
• Diatom sediment called diatomaceous earth used as abrasive and insecticide
  • To an insect, breathing in diatoms is like breathing in razor blades

Animal-like Protists

Euglena

Legend: flagellum: invisible tail, light detector: brown dot, green: chlorophyll

Many scientists incl. Euglena w/ plant-like protists

• animal-like protists: heterotrophic protists that capture and ingest food
• All unicellular heterotrophs found in aquatic or moist environments
• 3 main phyla classified by locomotion or parasitism

Phylum Sarcomastigophora

Amoeba

• Subphylum Sarcodina (the amoebas)
  • use pseudopods (false feet) to encircle and engulf prey
  • creates vacuole around prey, replaces water w/ digestive enzymes
• Subphylum Mastigophora (the flagellated protozans)
  • self-flagellate: to whip yourself

Amoeba Anatomy

Phylum Ciliophora

• The ciliates
• Move extremely fast by small hairs called cilia
• i.e. paramecia (sing. paramecium)
• cilia sweep food into oral groove
• food pushed into food vacuole and digested
• vacuole passes through organism to anal pore to release wastes

Paramecium Anatomy

Ciliate Anatomy Explained

Phylum Apicomplexa

• Parasitic protozoans, like Plasmodium which causes malaria
• Malaria kills ~800,000 people a year
• Affects mostly poor, developing nations
• Quinine: class drug for malaria
• Tonic water (had quinine) also used to treat / prevent malaria
• Malaria used to be prominent in S. USA

Malaria Lifecycle

Malarial Zones

Fungi-like Protists

• fungi-like protists: heterotrophic protists that feed mostly on decaying organic matter
• Main division Myxomycota
• plasmodial slime moulds: large, branching fungus-like protist
• cellular slime moulds: decomposers that live mainly on decaying organic matter
• water moulds: decompose dead plants and matter in freshwater habitats
• plasmodium: single mass of cytoplasm undivided by cell membranes or cell walls that contains many nuclei
• Exist as thin streaming masses
• Live in moist environments like rotting logs
• Consume bacteria, yeast, fungi, decaying plant and animal matter
• Many nuclei
• Capable of sexual reproduction

Reproduction

• Various strategies
• Amoebas, paramecia, and most ciliates
  • make copy of genetic material and divide into 2 genetically identical cells
  • lack genetic diversity
• Paramecia
  • exchange genetic material via conjugation
  • creates genetic diversity

Climate Change

• carbon dioxide in water forms carbonic acid
• lowers pH of aquatic environments
• most organisms have an optimum pH range
• large organisms tolerate pH changes better than small ones
• phytoplankton are sensitive to pH changes
• phytoplankton form the base of aquatic food chains
• their decline could collapse ocean food webs