Kingdom Protista – Characteristics and Classification

Kingdom Protista

·  The term ‘Protista’ is derived from the Greek word “protistos”, meaning “the very first“. 

· These Organism are classified under Kingdom Protista in Five Kingdom Classification by Robert H. Whittaker. Kingdom Protista includes all the unicellular eukaryotic organisms.

· This kingdom forms a link with the others dealing with plants, animals and fungi, but the boundaries of this kingdom are not well defined.

·  They are usually Single-celled and the cell of these organisms contains a nucleus which is surrounded by the organelles. They may also have structures that aid locomotion like flagella or cilia.

Characteristics of Kingdom Protista

All protists are eukaryotic organisms which means that they have a membrane-enclosed nucleus. Other Characteristics of Protista are as follows –

·  Usually aquatic (Marine or Freshwater), present in the soil or in areas with moisture.

·  They are diverse in their structure.

·  Majority of Protists are solitary but some exhibit colonial masses.

·  Mostly unicellular organisms, however, there are a few multicellular protists such as kelp. Some species of kelp grow so large that they exceed over 100 feet in height.

· Being eukaryotes, the Protista cell contains a well-defined nucleus and other membrane bound organelles.

·  Some protozoans form cysts – a type of resting stage.

· They may be photosynthetic, holotrophic, saprotrophic, parasitic and symbionts. Some have mixotrophic nutrition (holozoic + saprobic).

o  Some are photosynthetic like plants – are autotrophic

o  Some ingest their food like animals – heterotrophic by ingestion

o  Some absorb their food like bacteria and fungi – heterotrophic by absorption

o  One species Euglena is mixotrophic meaning that it is capable of both autotrophic and heterotrophic life styles.

·  The photosynthetic, floating protists are collectively called phytoplankton. The free-floating, holozoic protozoans are collectively termed zooplankton.

· Protists exhibit locomotion through cilia and flagella. A few organisms belonging to kingdom Protista have pseudopodia that help them to move.

·  Reproduction in Protists is of following types –

o      usually asexual by mitosis

o sexual reproduction involves meiosis and spore formation and usually occurs only when environmental conditions are hostile

o      spores are resistant and can withstand adverse conditions

Classification of Kingdom Protista

·  Protists are generally grouped into 3 categories –

1.    Plant-Like Protista

·  Referred to as algae. These are photosynthetic, found mostly in aquatic habitat.

·  They are further divided into –

a.    Chrysophytes,

b.    Dinoflagellates and

c.    Euglenoids.

2.    Fungus-Like Protista

·  Fungus-like protists are heterotrophs.

·  They are further divided into –

a.    Slime molds and

b.    water molds

3.    Animal-Like Protista

·  Referred to as protozoans (pro means ‘first,’ and zo refers to ‘animals’ – the first animals). They are heterotrophic and showed animal-like characters.

·  They are further divided into –

a.    Amoeboid protozoans

b.    Flagellated protozoans

c.    Ciliated protozoans

d.    Sporozoans

Economic Importance of Protists

·  Protists are a good food source and serve as the foundation of the food chain.

· Protists produce nearly half of the oxygen on the planet through photosynthesis, decompose and recycle nutrients and form a huge part of the food chain.

·  Blue-green and brown algae is currently being grown for biofuel.

·  Protists are the primary sources of food for many animals.

·  Phytoplankton and Zooplankton is one of the food sources for Marine Life.

· Protists are harvested by humans for food and other industrial applications. Chemicals from other kinds of algae are used to produce many kinds of plastics. Many Protists Species are also used for the Scientific Researches.


So, this was all about the Kingdom Protista – Characteristics of Protista and Classification. In the next post (Click here), we will discuss about the Plant like Protists in detail.

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