What is Protista? – Structure, Function, Characteristics

In the previous articles, we talked about Eukaryotic cells, their structure, examples, etc. And here in this section, we are going to discuss Protista, which is an example of a Eukaryotic cell, and at the same time, we will provide a comprehensive description of its structure, functions, as well as, its characteristics.  

What is Protista?

Before we delve into this topic deeply, let us first understand what a Protista is. As stated in the above section, Protista is defined as a special kind of Eukaryotic organism, and because of this, they are said to be unicellular in nature. However, they often form colonies and are commonly found in damp terrestrial environments, aquatic ecosystems, etc. Moreover, Protista is also considered as a parasite.  

Besides, this Protista is considered to be the link between plants and animals as well as fungi, as they are said to diverge from a similar singular cellular organism, that existed millions of years ago. And this is why Protista is said to be the very first eukaryotic form of life. 

Structure of Protista

Structure of Protista

From the above picture, you can find the various components of Protista such as Nucleolus, Golgi Apparatus, Stigma, Flagellum, Nucleus, Stored Carbohydrate, Endoplasmic Reticulum, Contractile Vacuole, Mitochondrion, etc. 

Classification of Protista

Generally, Kingdom Protista is defined into multiple categories such as,  

Slime Moulds

Slime moulds are small organisms that consist of many nuclei, and besides, they are unique as they food on decaying and dead, which is why they are generally referred to as Saprophytic organisms. Furthermore, the slime Moulds, unlike other Protista, can be viewed easily through the naked eye, due to the presence of aggregates like plasmodium. 


Protozoa are unique unicellular organisms, which have unique behaviour patterns similar to animals. That is why they are called animal protists, and they are also heterotrophic in nature. Apart from this, there are also parasitic protozoans that are commonly found in the bodies of large animals. Amoeba, Euglena, and Paramecium are popular examples of parasitic protozoans. Furthermore, the protozoans can be further divided into four types, such as,  

  • Sporozoans – Because of their spore-like stages of life, these protozoans have earned the name Sporozoans.  
  • Amoeboid Protozoans – As the name itself suggests, these species are limited mostly to water bodies, both saline and fresh. Besides, these organisms have unique characteristics such as Pseudopodia, which play a major role in helping them consume food, while also allowing them to change shape. 
  • Ciliated Protozoans – Similar to the Amoeboid protozoans, these are also aquatic, and more importantly, their cilia are located all over the body, which in turn will provide nutrition for the species, and at the same time, also helps in locomotion. 
  • Flagellated Protozoans – The Protozoans which have flagella are called Flagellated Protozoans. One of the unique features of these protozoans is, they can live as parasites and free-living organisms. 

Chrysophytes, Euglenoids, and Dinoflagellates

Unlike the above examples, these three organisms are under the special category known as Kingdom Protista. Besides, these organisms are both single-celled and multiple-cellular organisms. Each of these species has unique characteristics or functions. For instance, the organisms that have cell wall deposits, and are photosynthetic in nature are called Chrysophytes. 

While the organisms which showcase bioluminescence, and are one of the main reasons behind red tide are known as Dinoflagellates.  Then there are the Euglenoids which act as a link between plants and animals, as their food is varied based on the presence of sunlight. 

Characteristics of Protista

Now that we have a good understanding of the various types of Protista, and its structure. Let us now talk about the Characteristics of Protista. Firstly, you must remember that the Kingdom Protista species have various characteristics that make them unique from other similar species. 

  • As explained above, most of the Protista species are aquatic or semi-aquatic, as they thrive only in regions where there is high moisture. 
  • Besides, the reproduction process in the Protista is said to be asexual most of the time. However, in rare cases, sexual reproduction is also observed. 
  • Unlike other organisms, the Protista can be heterotrophic or autotrophic in nature based on the presence of the sun. 
  • Furthermore, Protista has a unique characteristic known as Symbiosis, which allows them to have a symbiotic relationship with other organisms.  
  • The Protista being a Eukaryotic organism, generally consist of membrane-bound organelles and a nucleus. 
  • Some types of Protista have characteristics of parasitism, which means they can cause sleep sickness and various other diseases in humans. 
  • And lastly, Protista can be categorized as both uni-cellular as well as multi-cellular organisms. 

Importance of Protista

Here in this section, we are going to talk briefly about the Importance of Protista in much more detail. 

  • Protista acts as a food source for the majority of animals, including humans, who harvest Protista to make food. 
  • Seaweed which is an essential part of the aquatic ecosystem is a subcategory of Protista. 
  • Besides, Phytoplankton which is the main food source of dolphins and whales is a type of Protista. 
  • Then there is Zooplankton, which acts as food for small aquatic creatures such as Shrimp, Crabs, Small Fishes, etc. 
  • Apart from this, some of the Protista subspecies have the ability to produce oxygen which is why they are actively used in making biofuels. 


Here in the article, we have discussed the Protista Kingdom, Protista Examples, Kingdom Protista Classification, Protista Characteristics, and Types of Protista in detail. And as you already know, there are many other complex topics in biology subject, which can be very hard to learn on your own. In that case, we suggest the students join the exclusive online interactive classes offered by our Tutoroot platform. Where they will be able to access various amazing features such as Expert Staff Guidance, Doubt Clarification Sessions, Budget Friendly Prices, and many more. 

Frequently Asked Questions

Is Protista unicellular or multicellular? 

Protista species unlike other organisms can be both unicellular as well as multicellular in nature. 

Do protists have a nucleus? 

Yes, Protista being a Eukaryotic Organism, it consists of both nucleus as well as membrane-bound organelles. 

Where do protists live? 

Protista species are generally found in aquatic as well as damp terrestrial ecosystems. 

What are Slime Moulds? 

As explained above, Slime Moulds are a sub-variety of the Kingdom Protista, that is popularly known for its ability to have multiple nuclei, and dead & decay matter as its food source.   

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