Are Protists Unicellular? 9 Important Facts You Should Know


A unicellular organism contains a single cell with a well-defined nucleus. They all are eukaryotic and prefer to live in a moist environment. They possess some membrane-bound cell organelles, but mitochondria (hydrogenosomes in some species) are present in most species to reach the need for energy in the cell.

No, they are predominantly unicellular like algae (Cyanidioschyzon merolae) amoeba, paramecium and euglena, but some are coenocytic while few are also multicellular like some species of protozoa, slime moulds etc. They showed the very different life forms in which some of the members are hosts to other organisms.For example, Trichomonas vaginalis infects the human vagina and causes trichomoniasis, and Trypanosoma causes Sleeping sickness.

They are mostly microscopic. Some forms can reach up to the height of 60-65 metres or more and are capable of locomotion. They contain cilia and flagella as their locomotory organs. They perform both autotrophic and heterotrophic (phagotrophic and osmotrophic) nutrition. Beneath the pellicle, some extrucible bodies are present, termed as extrusomes like trichocysts, mucocysts, toxicysts etc.

Why are protists unicellular?

Protists are very diverse organisms as some forms involve one of the most famous ways of binary fission in which an individual splits into two daughter nuclei followed by cytoplasmic division. As per the recent studies, a few forms are also taking part in physical mechanisms but examples are not on good terms.

Are protists unicellular, So the answer is Yes. Based on the evolutionary relations, protists are introduced in 1866 by German scientist Ernest Haeckel. He gave the three-kingdom classification in which Protista lies at the third position after Plantae and Animalia. They are single-celled eucaryotes. They are unicellular because of having single-cell, can perform photosynthesize their food and can convert the inorganic matter to organic form. They could not form blastula but had cilia and flagella.

Unicellular protists examples

As most of the members of the kingdom protists are single-celled eucaryotes. This also includes some of the colonial forms and multicellular. A few examples of unicellular protists are given below:

  • Amoebas
  • Diatoms
  • Dinoflagellates
  • Pyrrophyta (Fire algae)
  • Protozoans (Plasmodium falciparum)
  • Zooflagellates (Leishmania and Trichosomas)
  • Slime mould (Dictyostelium, Physarum)
  • Water mould (Phytophthora infestans)
  • Green algae (Chlorella, Spirullina, Volvox)
  • Euglena
  • Paramoecium
  • Trypanosomes
  • Giardia intestinalis

Are animal-like protists unicellular or multicellular?

Kingdom protists possess very diverse characteristics as some of them are parasitic or free-living, autotrophic or heterotrophic, some have rigid cell walls while some species lack the cell wall. But instead of all these variant features, they are so-called eucaryotes and have more complex cell structures than bacteria.

Some protists are involved in heterotrophic nutrition, producing spores and having cilia or flagella as a locomotory organ through which they can move from one place to another. They release some useful secretory enzymes for the digestion of their food. These features depict their animal-like characteristics. And based on genetic background, they may share a common ancestor. They can be both unicellular and multicellular. Examples can be categorised into:

  1. Ciliates (Paramoecium aurelia)
  2. Sarcodina (Entamoeba histolytica)
  3. Zooflagellates (Leishmania tropica, Trypanosoma cruzi)
  4. Sporozoans (Plasmodium falciparum, Toxoplasma gondii)

 Are plant-like protists unicellular or multicellular?

Amongst this kingdom, most of them exhibit the characteristics of plants i.e., they contain chloroplast and can convert solar energy into chemical energy.

They perform both the mode of reproduction which is binary fission and fusion of haploid gametes respectively.They also have a well-defined cell wall like plants but differ in composition. They can be unicellular, colonial and multicellular. Examples of unicellular plant-like protists are grouped into:

  • Euglenoids (Euglena)
  • Diatoms (Pinnularia, Navicula, Chaetoceros, Thalassiosira pseudonana)
  • Dinoflagellates (Karenia brevis, Karenia mikimoto)
  • Red algae (Cyanidioschyzon merolae)
  • Green algae (Chlamydomonas reinhardtii)
  • Fire algae
  • Multicellular algae are- Sargassum, Laminaria, Ectocarpus, Fucus, Macrocystis, Gracillaria and Gelidium, and Anabaena.
are-protists-unicellular
Diatoms by electron microscope Image credit: Flickr

Are fungus-like protists unicellular or multicellular?

Fungi-like protists are also known as moulds. They are dependent on the autotrophs to get their nutrients and have a hard cell wall composed of a derivative of chitin.

They do not have any locomotory organ and reproduce by spore formation. They are mostly found in an aquatic environment with a fewer terrestrial member. They feed upon rotten logs, dead organic matter etc. They are lying in two categories: Slime moulds and water moulds.

  • Dictyosteliomycota (Dictyostelium purpureum, Dictyostelium discoideum)
  • Myxomycota (Protostelia, Acrasia, Plasmodiophorina)
  • Labyrinthulomycota (Labrinthulida)
  • Oomycetes (Phytophthora infestans, Plasmopara viticola)
File:D. purpureum.jpg - Wikimedia Commons
Dictyostelium purpureum
Image credit: Wikimedia commons

Are there multicellular protists?

Some of the protists are multicellular as, in their whole life span, they live with multiple cells. They are more complex in comparison to unicellular organisms as they possess many cell organelles to perform the necessary cellular function.

Multicellular protists are mostly algae while sometimes slime mould gets aggregated to form a colony. This colony appears like a multicellular celled stage. They are familiar to algae but large in size and form dense forests like under the sea beds.

Multicellular protists examples

Not more than a few species are multicellular like giant kelps, seaweeds, some red algae and brown algae. So are the examples:

  • Sargassum muticum
  • Laminaria saccharina
  • Ectocarpus siliculosus
  • Fucus spiralis
  • Macrocystis integrifolia
  • Anabaena azollae
  • Ulva lactuca
  • Gracillaria and Gelidium
Calcareous red seaweed. | Corallina officinalis is a calcare… | Flickr
Seaweeds (Red alga)
Image credit: Flickr
are-protists-unicellular
Kelp forest (Macrocystis)
Image credit: Flickr

Conclusion

Protists are eucaryotic and more complex than kingdom bacteria and archea. They may be unicellular or multicellular. They play an important role in the production of oxygen over this mother earth through photosynthesis as they act as algae. When they are present in animal form, they act as decomposers for the conversion of organic molecules. They prove themselves as a good parasite to cause multiple symptoms related to pathogenicity in plants as well as in animals.

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