Freshwater Microorganism Images

Hollywood Beach Florida Marine Microorganisms: Microscope Images

Protists are microscopical, unicellular eukaryotes. They live in almost any environment that contains liquid water. Many protists, such as the algae, are photosynthetic and are vital primary producers in ecosystems, particularly in the ocean as part of the plankton. Other protists, such as the Kinetoplastids and Apicomplexa, are responsible for a range of serious human diseases, such as malaria and others, such as the amoeba, can cause serious illness when their population gets out of control in the body.. Some protists are motile, able to move by using flagella, pseudopodia, or cilia, while others are unable to move. They may live on their own by absorbing energy from sunlight, or they may live symbiotically with a host organism. In some cases, protists may engage in a mutual symbiotic relationship, where they gain energy from the host, and perform some beneficial service in return, but often they are parasitic, simply leeching energy off of the host.

[wpbgallery id=38819]

Organisms originally arranged under Kingdom Protoctista included water molds, slime molds, algae, and similar eukaryotic unicellular microorganisms. Records indicate the smallest organism in Kingdom Protoctista are protists, microscopic single cell organisms such as protozoa. Historically, they were all placed into the kingdom of Protista, but this is no longer the case. They are incredibly diverse, and there is little to bind them together as a grouping except for the simplicity of their structure.

[wpbgallery id=38905]

In 1977, Carl Woese and his collaborators introduced the most crowded top-level system yet, with six kingdoms: Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Animalia. Then, in 1990, the system was simplified by Woese, and decreased to three domains: Bacteria, Archaea, and Eukarya. In some cases, protists form colonies of individuals, though the individuals are generally autonomous. Researchers originally referred these minuscule living beings to the kingdoms of larger organisms. Then, according to the characteristics that a given protist showed, they tried to refer it to the plant kingdom (in the protophyta or algae), the animal kingdom (in the protozoa) or to the fungal kingdom.[1]

This led to a great deal of doubtful classification, for example “algae” deprived of chloroplasts and which fed on other microorganisms, “moulds” endowed with amoeboid movements like animals, or “protozoans” anchored to the substratum by a foot like they were a plant. Intuitively, it is possible to understand why protists often possess characteristics common to animals, plants and fungi: the larger organisms derive from protists. In order to avoid confusion in the classification of these microorganisms, a kingdom has been created, so that they need not be referred to the animals, plants or fungi. Grouping things in kingdoms is arbitrary- in the history of life there is no clear-cut division between protists and eukaryotes.

Not all microorganisms are protists. Another “kingdom” contains unicellular microorganisms, the Monera bacteria belong to this kingdom. So what difference is there between bacteria and protists? This distinction is founded on the complexity of a cell’s organization. The cellular organization of bacteria is particularly simple -they do not have membranes binding their nuclear material. For this reason they are also named prokaryotes . The cellular organization of protists is more complex they have a membrane -bound nucleus and other organelles distinct from cytoplasm) They are therefore called eukaryotes (“true-nucleus”). Animals, plants and fungi, being derived from protists, are also eukaryotes.[2] [wpbgallery id=38907]


Nutrition in some different types of protists is variable. In flagellates, for example, filter feeding may sometimes occur where the flagella find the prey. Other protists can engulf bacteria and digest them internally, by extending their cell membrane around the food material to form a food vacuole. This is then taken into the cell via endocytosis (usually phagocytosis; sometimes pinocytosis).

Nutritional TypeSource of EnergySource of CarbonExamples
PhototrophsSunlightOrganic compounds or carbon fixationAlgae, Dinoflagellates or Euglena
OrganotrophsOrganic CompoundsOrganic CompoundsApicomplexa, Trypanosomes or Amoebae


Some protists reproduce sexually (gametes), while others reproduce asexually (binary fission).

Some species, for example Plasmodium falciparum, have extremely complex life cycles that involve multiple forms of the organism, some of which reproduce sexually and others asexually.[3] However, it is unclear how frequently sexual reproduction causes genetic exchange between different strains of Plasmodium in nature and most populations of parasitic protists may be clonal lines that rarely exchange genes with other members of their species.[4]

Role as pathogens

Some protists are significant pathogens of both animals and plants; for example Plasmodium falciparum, which causes malaria in humans, and Phytophthora infestans, which causes late blight in potatoes.[5] A more thorough understanding of protist biology may allow these diseases to be treated more efficiently.

Researchers from the Agricultural Research Service are taking advantage of protists as pathogens in an effort to control red imported fire ant (Solenopsis invicta) populations in Argentina. With the help of spore-producing protists such as Kneallhazia solenopsae the red fire ant populations can be reduced by 53-100%.[6] Researchers have also found a way to infect phorid flies with the protist without harming the flies. This is important because the flies act as a vector to infect the red fire ant population with the pathogenic protist.[7][8]

  1. INTRODUCTION TO THE PROTISTS / Giorgio Carboni, March 2000 / Translation edited by Giselle Walker / Copyright © Giorgio Carboni
  2. Definition of Protista: eukaryotic one-celled living organisms distinct from multicellular plants and animals: protozoa, slime molds, and eukaryotic algae.
  3. ^ Talman AM, Domarle O, McKenzie FE, Ariey F, Robert V (July 2004). “Gametocytogenesis: the puberty of Plasmodium falciparum”Malar. J. 3: 24. doi:10.1186/1475-2875-3-24.PMC 497046PMID 15253774.
  4. ^ Tibayrenc M, Kjellberg F, Arnaud J, et al. (June 1991). “Are eukaryotic microorganisms clonal or sexual? A population genetics vantage”Proc. Natl. Acad. Sci. U.S.A. 88 (12): 5129–33. doi:10.1073/pnas.88.12.5129PMC 51825PMID 1675793.
  5. ^ N. Campbell, J. Reese. Biology. 2008. pp. 583, 588
  6. ^ “ARS Parasite Collections Assist Research and Diagnoses”. USDA Agricultural Research Service. January 28, 2010.
  7. ^
  8. Text is available under the Creative Commons Attribution-ShareAlike License; additional terms may apply. See Terms of Use for details. Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization.
[wpbgallery id=38910]

Text and images are available under the Creative Commons Attribution-ShareAlike License; Following additional terms apply: We ask that you include the following link if you use our material:

Visit Save the Water™ for more information on water research and education.

Thank you.

Want to Donate?
Please contact us for gifts in kind - Mail your check to: P.O. Box 545934, Surfside, Fl 33154