AP Biology
Notes:  Protista II

Three groups of protists use pseudopodia, cellular extensions, to move and often to feed.

• Most species are heterotophs that actively hunt bacteria, other protists, and detritus.
• Other species are symbiotic, including some human parasites.
• Little is known of their phylogenetic relationships to other protists and they themselves 
  are distinct eukaryotic lineages.
  
    Rhizopods (amoebas): All unicellular and use pseudopodia to move and to feed. Pseudopodium emerge
  from anywhere in the cell surface. To move, an amoeba extends a pseudopod, anchors its tip, and then streams
  more cytoplasm into the pseudopodium.
• Amoebas inhabit freshwater and marine environments . They may also be abundant in soils.
• Most species are free-living heterotrophs.
• Some are important parasites.

Entamoeba histolytica which causes amoeboid dysentery in humans.   These organisms spread via
contaminated drinking water, food, and eating utensils.

8. Actinopod (heliozoans and radiolarians) “ray foot” Each axopodium is reinforced by a bundle of microtubules
covered by a thin layer of cytoplasm.

•    Most actinopods are planktonic.
• The large surface area created by axopodia help them to float and feed.
• Smaller protists and other microorganisms stick to the axopodia and are phagocytized by
   the thin layer of cytoplasm.
• Cytoplasmic streaming carries the engulfed prey into the main part of the cell.

heliozoans (“sun animals”) live in fresh water

• Their skeletons consist of unfused siliceous (glassy)
   or chitinous plates.  

radiolarian refers to several groups of mostly marine actinopods.

• In this group, the siliceous skeleton is fused into 
  one delicate piece.
• After death, these skeletons accumulate as an ooze
   that may be hundreds of meters thick in some seafloor 
  locations.  
                                                                                                                                                           
  

9.  Foraminiferans  forams

• almost all marine.
•  Most live in sand or attach to rocks or algae.  
• Some are abundant in the plankton.
• Forams have multichambered, porous shells, consisting  of organic materials  hardened with calcium carbonate.  
•  Pseudopodia extend through the pores for swimming,  shell formation, and feeding.
• Many forams form symbioses with algae.  
• Over ninety percent of the described forams are fossils.
• The calcareous skeletons of forams are important components of marine sediments.
• Fossil forams are often used as chronological markers to  correlate the ages of
  sedimentary rocks from different parts of the world.  

 10. Mycetozoa:( Slime molds)

• Any resemblance to fungi is analogous, not homologous, for their convergent role in the decomposition
  of leaf litter and organic debris.
• Slime molds feed and move via pseudopodia, like amoeba, but comparisons of protein sequences place slime molds     
  relatively close to the fungi and animals.

plasmodial slime molds (Myxogastrida) are brightly  pigmented, heterotrophic organisms.

• The feeding stage is an amoeboid mass, the plasmodium that may be several centimeters in diameter.
•   The plasmodium is not multicellular, but a single mass of cytoplasm with multiple nuclei.
• The diploid nuclei undergo synchronous mitotic divisions perhaps thousands at a time.
•   The plasmodium phagocytises food particles from moist soil, leaf mulch, or rotting logs.
•   If the habitat begins to dry or if food levels drop, the plasmodium differentiates into stages that lead to
  sexual reproduction.

  cellular slime molds (Dictyostelida) 

•   straddle the line between individuality and multicellularity.
• The feeding stage consists of solitary cells.
• When food is scarce, the cells form an aggregate (“slug”) that functions as a unit
• The dominant stage in a cellular slime mold is the haploid stage.

• Aggregates of amoebas form fruiting bodies that produce spores in asexual reproduction.
• Most cellular slime molds lack flagellated stages.