Since our lower classes; we have been learning about diversity in living organisms. We have also learned about 5 Kingdom system of classification given by R.H Whitaker.

Remember no? Well! It includes Kingdom Monera, Protista, Fungi, Plantae&Animalia.  Here I am going to tell you about very interesting category of Kingdom Protista which is protozoa.


Fig: Paramecium (a type of protozoa)

For the first time, protozoans were studied by Leeuwenhoek (1677). Name protozoa were coined by Goldfuss.Branch of biology in which we study about Protozoa is known as protozoology.

Let me tell you classification of protozoa now. Take a look to this flowchart first. Then I’ll tell you details.


Flagellated Protozoans –

Characteristics –

  • Flagella is present & it helps in locomotion
  • Both sexual & asexual types of reproduction occur.
  • They may be parasitic, free living, aquatic, commensals or symbionts.
  • Zooflagellates may be uninucleate or multinucleate.
  • Heterotrophic nutrition may be holozoic, saprobic or parasitic.

Now let’s take a look to certain flagellated protozoans.


  • Trypanosoma gambiense– It is a parasite of sleeping sickness. This pathogen is transmitted by tse tse fly.  They absorb the food by body surface.
  • Leishmania donovani – It causes Kala azar or dum-dum fever. This pathogen is transmitted by sandfly.
  • Giardia intestinalis(Giardia lambia)-  It is commonly nicknamed as ‘grand old man of intestine’. It causes giardiasis.
  • Trichomonas vaginalis–It used to be present in vagina of women. It causes leucorrhoea disease. Transmission of this disease occur by coitus (intercourse)

Amoeboid Protozoans –

Characteristics –

  • Temporary pseudopodia are formed in them which are the body outgrowth.
  • Living body is covered by plasmolemma or a shell.
  • Holozoic nutrition.
  • Both sexual & asexual reproduction occurs.

Some of the examples are:


  • Amoeba Proteus – This is the most common microorganism which you are learning since your lower classes.  You know it was discovered by Russel von Rosenhoff (1755). Food ingestion & digestion occurs by phagocytosis.
  • Entamoeba histolytica-It was discovered by Lamble (1859). It causes amoebic dystentry (amoebiasis). You know medicine for this disease is Metrogyl or Flagyl.
  • Heliozoans(sun – animalcules)- They have spherical structures. Their pseudopodia are radiating.

Sporozoans –

Characteristics –

  • They are endoparasites.
  • Some of them are disease causing also (e.g. Eimeria).
  • Locomotory organs re absent.
  • Parasitic nutrition
  • Phagotrophic.
  • Both sexual & asexual type of reproduction occurs.

Here again, you have to learn certain examples.


  • Plasmodium – It is the malarial parasite. Its carrier is female anopheles mosquito only.Male mosquito feed on plant sap. This parasite doesn’t harm the mosquito itself.
  • Monocystis–It is present in the seminal vesicle & coelom of earthworm. Locomotory organs are present in them.
  • Eimeria– this pathogen causescoccidiosis disease in animals.

Ciliated protozoans –

Characteristics –

  • They possess a number of cilia.
  • They show high degree of morphological & physiological specialization.
  • Nutrition is holozoic & parasitic as well.
  • Dimorphic nucleus is present (macro & micronucleus).
  • Ciliates show defense mechanism by producing ejectable trichocyst.
  • Both sexual & asexual reproduction occurs.

Time to read examples again 28

  • Paramecium (slipper organism)– It is a free living ciliate. They are of two types viz. Kappa (killer) paramecia & sensitive paramecia.

             You know paramecium exhibits cytoplasmic inheritance in the presence of kappa particles.

  • Vorticella–They are inverted, stalked & bell shaped. There are 16 known species of vorticella. They are freshwater microorganisms.
  • Opalina –They are present in intestine of frog & toads. Their body shape is leaf like. They show saprotrophic types of nutrition.
  • Balantidium– It is endoparasite of intestine. It causes ciliary dystentry. Its transmission is through food and water.

I think I should mention about myself too now. I am Anjali Ahuja, one of the members fromaskIITians pool. Our main motive is to help students in stepping up the stair. We have created study resources in this regard. I’m pretty sure; it is going to help you. So all you need to do now is to jump in this link.

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