Protozoans are the microorganisms present on land and water.
These are the animals that 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 protozoan 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 are 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 more hypertonic than the surrounding fresh water, 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 even to have sexual means of reproduction.
Some types of amoeba also cause severe diseases in 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, and these cilia help in its locomotion.
- They are found in freshwater and are more evolved than the amoeba.
- They have a mouth, cilia, and vacuoles for the expulsion of waste out of the cell.
- They undergo sexual reproduction by the method of conjugation.
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.
- L. Donovani infects the liver, spleen, white blood cells, etc.
- It causes kala-azar (dum dum fever) and visceral leishmaniasis.
- In comparison, 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 plasmodium falciparum is considered to be deadly as it is responsible for 50% of malarial cases.
- 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 African 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.
- A first host is a man or animal and the second host is an insect called a 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, a few of them are also parasites.
Read more on single-celled organisms.