Protozoans are the microorganisms present on land and water.
These are the animals which have a single cell yet live independently. They are
These protozoans are of different shapes and sizes with varying habitats. Many of them are free-living while others live as parasites.
They perform all of their physiology, including reproduction, movement, food collection with that single cell.
Protozoa Examples Include
Amoeba is a protozoan that has no specific shape. It is the most common protozoans found in freshwater. They live independently and move in search of food. Most freshwater protozoa are microscopic.
They cannot be viewed with naked eyes and need the help of a microscope. But, the marine amoebas big in size comparatively and are visible to the naked eye.
The structure is so simple, with no specialized appendages or sexual parts. They move by pseudopodia, which are the extensions of the cell membrane and cytoplasm. The cell has a contractile vacuole, which helps to remove excess water from the cell.
Since the cell cytoplasm is hypertonic than the surrounding freshwater, the water tends to accumulate inside the cell. The vacuole expels this accumulating water out.
They do not have a mouth but engulf solid particles by phagocytosis from any point of the cytoplasmic membrane.
They also drink dissolved forms of liquid nutrients by pinocytosis. Their food includes live microbes like bacteria and also dead organic matter.
They reproduce by binary fission asexually. But recent studies showed them to even have sexual means of reproduction. Some types of amoeba also cause severe diseases to humans.
This is an eye-shaped freshwater protozoan. They impart the green color to the water ponds when grown extensively. Unlike amoeba, they have well developed with cell organelles like eyespot (Stigma), flagella, etc.
Unlike amoeba, they can act as autotrophs, as they make their own food. The eyespot contains chlorophyll like pigment by which they perform photosynthesis.
They can also live as heterotrophs and eat external substances. Hence they have both plant and animal characters.
This is a slipper-shaped protozoan. It has cilia all over its body surface. These cilia help in its locomotion.
They are found in freshwater and more evolved than the amoeba. They have a mouth, cilia and also go for sexual reproduction.
4. Entamoeba histolytica
This is an amoeba that infects the large intestine and other tissues. It spreads through contaminated water and food. It is anaerobic and resides in a low oxygen atmosphere.
The infection causes severe pain in the abdomen and loose stools with mucus. Unlike typical amoeba, it has a single pseudopod. It is a mono-genetic parasite, i.e., completes its life cycle in man (single host). In the intestine, it resides in the mucous and sub-mucus layers. It secretes an enzyme, namely “Histolysin,” which dissolves the mucus tissue.
5. Trichomonas vaginalis
It is a protozoan that causes vaginal infection in humans. The protozoa are flagellate and also anaerobic. It is a type of sexually transmitted disease.
The symptoms of infection do not appear in women but appear in men.
Leishmania is of two kinds as Leishmania donovani and Leishmania Tropica. Donovani infects the liver, spleen, white blood cells, etc. It causes kala-azar (dum dum fever) and visceral leishmaniasis. In comparison, the L.tropica affects the endothelial cells of skin capillaries. The infection is spread by sandflies.
Commonly known as a malarial protozoan parasite. It is spread from human to human by the bite of a female Anopheles mosquito. This protozoan is of 4 types like plasmodium vivox, P. falciparum, P. malaria, P. ovale. Of them, the last one is deadly.
The protozoa in humans reside in the red blood cells. It eats up hemoglobin and converts it into a poisonous substance Haemozoin. When the RBC breaks down, the hemozoin is released, causing chills, headaches, and fever. They have a cycle of 24 hours so, they break down the infected RBC and attack news one every 24 hours. So the infected person experiences feverish symptoms in intervals of 24 hours.
8. Trypanosoma gambiense
This is a protozoan that causes sleeping sickness. They are spread by the bite of a tsetse fly.
The parasite is oval-shaped and has flagella. It is a digenetic parasite. The first host is man or animal and the second host is an insect called tsetse fly.
9. Giardia intesinalis
It is an intestinal parasite residing in the small intestine. It causes abdominal pain and diarrhea.
It is spread by contaminated water. As seen in the picture above, it has two nuclei and 4 flagella. They do not possess mitochondria and instead, a modified endomembrane complex helps in energy generation.
10. Balantidium coli
It is a ciliated parasitic protozoan living in the large intestine.
As seen in the picture below, it has two nuclei. One large and one small nucleus lying close to each other. A mouth called cytosome or peristome is present.
The transmission to man occurs from pigs. It causes ulcers and chronic dysentery.
These are bell-shaped ciliates living in mud and freshwater. They eat bacteria and sometimes survive on the surfaces of mosquitoes, prawns, etc.
While moving, they make a vortex in the water and hence the name.
These are trumpet-shaped protozoa. They dwell in freshwater and some are found in marine waters. They have a symbiotic relationship with few algae.
Protozoan’s physical structure is a simple cell. They have a distinct nucleus and other essential organelles and also possess the ability to move. They multiply by sexual and asexual reproduction types. Most of them are harmless and habitat in freshwater or seawater. Some of them make their food by photosynthesis, while others are dependent on other organic debris for food. To the extreme, few of them also parasites.
Read more on single-celled organisms.