Protozoans a single celled organisms which live independently. The examples of protozoa are many.
Of them some are free living while others are parasites.
Being single celled, they appear similar to bacteria.
But unlike bacteria, they are eukaryotes and do not possess cell wall.
Further they have characteristics similar to animals.
Most of them are harmless and live in fresh water around.
Some of them rely on photosynthesis or other organic debris for food while others live as parasites.
Their physical structure is simple. They have a distinct nucleus and are able to move.
They multiply by sexual and asexual reproduction types.
Examples of Protozoa
1. Amoeba: This is a shapeless protozoa. It is the most common type of protozoa and studied as first one in the class. They live individually and have ability to move and find food.
The structure is so simple with no special appendages or sexual parts. They move by pseudopodia which are extensions of cell membrane and cytoplasm. They do not have mouth but just engulf solid particles by phagocytosis and drink liquids by pinocytosis. They reproduce by binary fission asexually. But recent studies show them to even have sexual means of reproduction. Some types of amoeba also causes severe diseases to humans.
2. Euglena: An eye shaped fresh water protozoa. It imparts green color to the water ponds. Unlike amoeba seems to be well developed with some special organelles like eye, flagella etc.
Unlike amoeba, they can act as autotrophs i.e. make their own food. They contain chlorophyll like pigment by which they performs photosynthesis. They can also act as heterotrophs and eat external substances.
3. Paramecium: This is a slipper shaped protozoa. It has cilia all over its body surface. These cilia helps in its locomotion.
They are found in fresh water and more evolved than amoeba. They have a mouth, cilia and also go for sexual reproduction.
Disease causing protozoa
4. Entamoeba histolytica: This is an amoeba which infects large intestine and other tissues. It spreads through contaminated water and food. It is anaerobic and resides in low oxygen atmosphere.
The infection causes severe pain in the abdomen and loose stools with mucus. Unlike typical amoeba, it has a single psuedopodia. It is a mono-genetic parasite i.e. completes it life cycle in man. In the intestine it resides in the mucous and sub-mucos layers. It secretes an enzyme namely “Histolysin” which dissolves mucus.
5. Trichomonas vaginalis: A protozoa which causes vaginal infection. It is a type of sexually transmitted diseases. The protozoa is flagellate and is anaerobic.
6. Leishmania: Leishmania is of two types as lesihmania donovani and leishmania tropica. Donovani infecs liver, spleen, white blood cells etc. It causes kala-azar (dum dum fever) and visceral lesihmaniasis. While the L.tropica infects the endothelial cells of skin capillaries. The infection is spread by sandflies.
7. Plasmodium: Commonly known as a malarial parasite. It is spread from human to human by the bite of a female anopheles mosquito. This protozoa is of 4 types like plasmodium vivox, plasmodium falciperum, plasmodium malariae, plasmodium ovale. Of them Plasmodium falciperum is deadly.
The protozoa in the humans resides in the red blood cells. It eats up hemoglobin and converts it into a poisonous substance Haemozoin. When the RBC breaks down, the haemozoin is released causing chills, head ache and fever.
8. Trypansoma gambiense is protozoa which causes African sleeping sickness. They are spread by bite of tsetse fly.
The parasite is oval shaped and has flagella. It is a digenetic parasite. First host is man or animal and second host is an insect tsetse fly.
9. Giardia intesinalis: It resides in small intestine and causes dysentery.
10. Balantidium coli: It is a ciliated protozoan residing in large intestine.
It causes ulcer, chronic dysentery. The transmission occurs from man to pig and man to pig.