2.4: Protists-Unicellular Eukaryotes

Classification: Protists

• grouped together with organisms that don’t fit into other kingdoms
  • catch-all kingdom
• major groups only distantly related
• most protists are unicellular
  • eukaryotic

Animal-Like Protists

• consume other organisms
  • Cercozoans
  • Ciliates
  • Flagellates
  • Sporozoans
• often called protozoans
• heterotrophs
  • consume other organisms for food
• some are parasites
  • live on or in another organisms at the expense of that organism

Cercozoans

• internal cytoskeleton to move and create different forms
• pseudopods
  • used for feeding and locomotion
  • temporary cytoplasmic extensions
• live in aqueous environments
  • salt or freshwater, mud, humans
• free living and parasitic
• feed through phagocytosis
  • process when a cell engulfs a particle and digests it

Entamoeba hystolitica

• feeds on small intestine lining of humans
• causes amoebic dysentery
• spread by contaminated water or produce

Ciliates

• most familiar are paramecia
• cilia
  • tiny hair like projections covering cell surface
  • feeding and locomotion
  • free living and parasitic
  • large and complex
  • over 100 micro metres in length

Balantidium coli

• only known disease causing species of ciliates
• lives in large intestine
• causes diarrhea

Flagellates

• organisms with one or more flagella
  • long hairlike projections extending from cell membrane
  • used to propel cell (whip like motion)
• called zooflagellates
• hard protective shell covering outer membrane

free living, parasitic, mutualistic

Trichonympha

• mutualistic relationship with termites
• live in termite gut and produce enzymes
  • convert wood into sugar

Giardia

• causes giardiasis
• most common cause of waterborne disease
• found in backcountry streams, lakes, public water

Trypanosoma

• causes African sleeping sickness
• vector borne parasitic disease
• transmitted through tsetse fly bites
• can affect nervous system
  • changes of behaviour, confusion, sensory disturbances, poor coordination, sleep disturbance
• fatal without treatment

Sporozoans

• produce spores
  • reproductive structures capable of growing a new individual
• parasitic
• life cycles alternate between two hosts
  • vector (where spores mature)
  • mosquitoes
  • host (where spores are produced)
  • humans

Plasmodium

• causes malaria
• requires a mosquito vector to carry spores
• attacks red blood cells
• symptoms are fever, chills, nausea, vomiting
• kills 2 million people per year

Fungus-Like Protists

• visible to the unaided eye as tiny, slug-like organisms
• creep over damp, decaying plant material
• contains many nuclei
• have cell walls
  • walls made of chitin instead of cellulose
• heterotrophs
  • engulf small food particles into cytoplasm
  • saprotrophs

Plasmodial Slime Moulds

• represent vast diversity of morphologies
• difficult to distinguish
• form varied, distinct shapes once formed into a fruiting substance
• feed by engulfing small particles into cytoplasm
• spreads through spores
• streaming blob is called a plasmodium
  • NOT THE SAME AS OR RELATED TO SPOROZOAN PLASMODIUM

Cellular Slime Moulds

• individual amoeboid cells that periodically aggregate
  • form a pseudoplasmodium
  • aggregate forms fruiting body
  • produces spores

Dictyostelium discoideum

• important for understanding cell differentiation
  • single celled and multi celled life stages
• cells showed differentiation while multi celled
• cells gather together when food is scarce
  • pseudoplasmodium
  • still retain individual cell structure while looking like a single mass

Water Moulds

• filamentous organisms resembling fungi
• most live on dead organic material
• some are parasitic
  • fish, insects, plants
  • extend filaments into host tissues
• release digestive enzymes to absorb nutrients

Phytophthora infestans

• destroys leaves and edible tubers of potato plant
• caused Irish famine

Unicellular Plant-Like Protists

• contains pigments in chloroplasts to carry out photosynthesis
• includes diatoms, dinoflagellates, and euglenoids

Diatoms

• phytoplankton
  • single celled and free floating aquatic organisms
• most abundant and diverse of phytoplankton
• rigid cell walls
  • outer layer of silica
  • found in sand and glass
• play important role in marine ecosystems
  • important food source for larger organisms
  • primary source of photosynthesis and oxygen production in the ocean
• reproduce asexually usually, can reproduce sexually under certain conditions

Dinoflagellates

• phytoplankton
• two flagella at right angles to each other
  • movement of flagella results in dinoflagellates spinning through water
• covered in armoured plates of calcium carbonate
• reproduce very quickly
  • results in population explosions called algal blooms
  • can occur because of changing water conditions

Red Tides

• caused by algal blooms
• dinoflagellates release toxins into water
  • harmful to fish and humans
  • toxins can accumulate in fish that we consume
  • impede nervous system
  • can breathe in toxins
• tides can be different colours depending on protist

Symbiodinium

• live inside of corals (mutualistic)
• corals release nitrogens for protists, protists perform photosynthesis for corals
• coral bleaching occurs when dinoflagellates get expelled from corals
  • happens because of rising water temperatures

Euglenoids

• most familiar is Euglena
• found in shallow freshwater
• have chloroplasts, are photosynthetic, also have flagella and can absorb nutrients
  • autotrophs in sunlight
  • heterotrophs in dark
• have an eyespot to detect light
  • allows protist to use flagella to move towards light