|MadSci Network: General Biology|
Kristen - Thanks for the question. The answer to this question lies in the number of cells (i.e. is it single cell or multicellular organism?). In general, a protist is a free living, single cell eukaryote (as opposed to bacteria which are prokaryotes). Since protists are eukaryotic, they have membrane bound organelles (golgi body, mitochondria, etc.) AND a membrane bound nucleus (conversely, prokaryotes have no membrane bound organelles or membrane bound nucleus). So: if the organism observed under the microscope is a single cell and if a true nucleus and organelles can be identified, then it is a protist. If the organism is multicellular, then it is not a protist). Protists can be photosynthetic or carnivorous for energy aquisition. In your case, it seems to be carnivorous. The "feeding mechanism" used by protists is called phagocytosis. Phagocytosis is when a cell engulfs a particle, internalizing it. Once a particle (which could be food or even another organism) is phagocytosed, it undergoes processes to digest it into nutrients utilizable by the cell. Catagories of protozoa (which tend to be larger and more versitile than protists) include: amoebae, euglena, and ciliates (Paramecium species fall under this catagory). In addition to being found in tidal pools, protozoa can also be found in other water supplies. Protozoa within some water supplies can be a problem, because they are the causitive agent of some human diseases. Hope that this helped! Glynis Kolling Graduate Student, Food Microbiology Rutgers University, NJ
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