2. Kingdom Protista:

This group includes all the unicellular but eukaryotic organisms. These organisms show link with all eukaryotic Kingdoms like Plantae, Fungi and Animalia.

a. Plant like protista:

  • They are also termed Chrysophytes.
  • They are commonly termed phyto-planktons.
  • They are microscopic and mostly photosynthetic and are major producers in oceans.
  • Most of them are referred to as diatoms as the have body wall made up of two soap-box like fitting silica covers.
  • "Diatomaceous earth" is nothing but these shells left behind for so many years. Diatomaceous earth is granular hence finds use in polishing and filtration.

 Related image

b. Animal like Protista

  • They are also termed protozoans.
  • They lack cell wall.
  • They are heterotrophs.
  • They are believed to be primitive animal forms.
  • Amoeboid protozoans have pseudopodia as locomotory organs. Amoeba is free living form but Entamoeba is endoparasite and causes amoebic dysentery.
  • Flagellated protozoans have flagella as locomotory organ. Trypanosoma is a common flagellated pathogen which causes sleeping sickness.
  • Paramoecium is a cilliate protozoan having cilia for locomotion. In Paramoecium, gullet (a cavity) opens on the cell surface.
  • Plasmodium is a sporozoan protozoa. It causes malaria. It forms spores in one of its life stage.

Paramoecium

c. Dinoflagellates

  • These are aquatic (mostly marine) and photosynthetic.
  • The cell wall is made up of cellulosic stiff plates.
  • They possess a pair of flagella.
  • They have a wide range photosynthetic pigments, which can be yellow, green, brown, blue and red.
  • Gonyaulax is dinoflagellate that is responsible for famous 'red tide'. It makes even sea appear red.

d. Fungi like protista :

  • They are commonly from the group Myxomycetes.
  • These are saprophytic organisms found on decaying leaves.
  • Their cells aggregate to form a large cell mass called plasmodium (not a malaria parasite).
  • The spores produced by plasmodium are very tough and survive even very harsh conditions.

e. Euglenoids

  • They lack cell wall but have a tough covering of proteinaceous pellicle.
  • They possess two flagella, one short and other long.
  • They behave as heterotrophs in absence of light but possess pigments, similar to that of higher plants, for photosynthesis.

Euglena