Class 11 Biology Biological Classification Kingdom Protista

Kingdom Protista

  • All single-celled eukaryotes are placed under Protista.
  • Chrysophytes, Dianoflagellates, Euglenoids, Slime moulds and Protozoans are under Protista.
  • The protistan cell body contains a well-defined nucleus and other membrane-bound organelles.
  • Protists reproduce asexually and sexually by a process involving cell fusion and zygote formation.


  • This group includes diatoms and golden algae (desmids), found in fresh water as well as in marine environments.
  • In diatoms the cell walls form two thin overlapping shells embedded with silica.
  • diatoms have left behind large amount of cell wall deposits in their habitat, which accumulated over billions of years is referred to as ‘diatomaceous earth’ .
  • Most of them are photosynthetic and are the chief ‘producers’ in the oceans.


Fig. Chryosphytes

  • Mostly marine and photosynthetic.
  • The cell wall has stiff cellulose plates on the outer surface.
  • Yellow, green, brown, blue or red pigments are present in their cell.
  • Most of them have two flagella; one lies longitudinally and the other transversely in a furrow between the wall plates.
  • Red dianoflagellates undergo such rapid multiplication that they make the sea appear red (red tides). Example: Gonyaulax.


Fig. Dianoflagellates

  • Majority of euglenoids are fresh water organisms.
  • They have a protein rich layer called pellicle which makes their body flexible.
  • They have two flagella, a short and a long one.
  • They are photosynthetic in the presence of sunlight, when deprived of sunlight they behave like heterotrophs.

Example- Euglena


Fig. Euglena

Slime Moulds

  • Slime moulds are saprophytic protists.
  • Under suitable conditions, they form an aggregation called plasmodium, and during unfavourable conditions, the plasmodium differentiates and forms fruiting bodies bearing spores at their tips.
  • The spores possess true walls, and they are extremely resistant and survive for many years.


  • All protozoans are heterotrophs and live as predators or parasites.


Fig. Protozoans

  • There are four major groups of protozoans
  1. Amoeboid protozoans:
  • These organisms live in fresh water, sea water or moist soil.
  • They show Amoeba like movements and move and capture their pray with the help of pseudopodia.

Example- Entamoeba,  a parasite.


Fig. Entamoeba

  1. Flagellated protozoans:
  • The members of this group are either free-living or parasitic, and have flagella.
  • The parasitic forms cause diseases such as sleeping sickness.
  • Example: Trypanosoma.


Fig. Trypanosome

  1. Ciliated protozoans:
  • These are aquatic, actively moving organisms because of the presence of thousands of cilia.
  • They have a cavity (gullet) that opens to the outside of the cell surface.

 Example: Paramoecium


Fig. Paramecium

  1. Sporozoans:
  • Sporozoans includes diverse organisms that have an infectious spore-like stage in their life cycle.
  • The most notorious is Plasmodium (malarial parasite) which causes malaria.


Fig. Plasmodium

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