What is Protozoology?

The term protozoology defined the study of protozoans. In the latter half of the 17th century, Netherland scientist Antonie van Leeuwenhoek first observed the protozoans under a simple microscope.  A person who was specialized in protozoology is known as protozoologists. Protozoans are common and can easily found around the world. Many protozoans show particular interest in human beings. As they cause various diseases like amoebic dysentery, malaria, and African trypanosomiasis. Certain protozoans will have an extensive fossil record, they are termed foraminifera. They are much useful for the geologist to locate petroleum deposits. Also, researchers are widely using the protozoans as an experimental organism during the study of cells and molecular biology. 

What are Protozoans? 

Protozoans are the plural form of protozoa or protozoan. The protozoa is a subkingdom, which comes under the kingdom Protista. But they are commonly placed under the kingdom called Animalia. More than 50,000 free-living species have been described under the sub-classification protozoa. Protozoans are the single-celled organisms found across the world in most habitats. Many protozoan species are free-living, but they cause diseases to higher animals. Infection caused by them ranges from asymptomatic to life-threatening. The infection ranges are completely depending on the species and strains of the parasites and their host resistance. According to Protozoology, the shells in sedimentary rocks holds the fossil records of protozoa, which were present in the pre-Cambrian era. Usually, all organisms will have protozoa in their body but only a few species cause infection to the host. 

Where Can We Find Protozoans?

Protozoans are widely found in moisture habitats. As the protozoans are small in size, they are easily distributed from one place to another. Marine protozoans will settle in the beach stand, the surface of the water, deep sea, planktonic habitats, algal mats, and antarctic cols environments. The temperature availability, oxygen requirements, and salinity are poor for marine protozoans. The polluted waters will offer rich characteristics for protozoans. Likewise, the soil-dwelling protozoans are widespread over the dry sands of deserts and other various types of soil surfaces. In general, protozoans are widely distributed near the soil surface. 

Structure of Protozoans

Protozoans are the unicellular microscopic eukaryotes, which have relatively complex internal structure and they can carry out complex metabolic processes. Some protozoans have propulsion structure and others will have movement. The size of the human parasitic protozoans ranges less than 50 μm. The smallest protozoa are ranged between 1 to 10 μm long. As protozoans are eukaryotes, the nucleus is enclosed in a membrane. Except for ciliate protozoa, all others have a vesicular nucleus. The protozoan organelles have similar functions to the organs of higher animals. Also, protozoans will have projections for helping the locomotion of species. They are cilia, pseudopodia, and flagella. Some protozoa have pellicles on their outer surface. They are sufficient to maintain a distinctive shape. 

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Protozoans Life Cycle 

Protozoa life cycle falls under different stages and they have a wide difference in structure and activity. The protozoa will frequently multiply and actively feed in a particular stage. This stage is known as trophozoites.  The trophozoites in greek means ‘animal that feeds’.  These stages are usually associated with pathogenesis in parasitic species. While coming to hemoflagellates protozoans, it terms amastigote, epimastigote,  promastigote, and trypomastigote during the trophozoite stages. Here the presence and absence of flagellum and its position of kinetoplast will relate to it. The stage of Apicomplexa is termed tachyzoite and bradyzoite. The Merozoite stage can observe both during sexual and asexual reproduction of protozoa. During sexual reproduction, the protozoa go under gametocytes. Some protozoa go under the cysts stage, which is the protective membrane around the species. Usually, multiplication occurs inside the cysts and releases more than one organism. 

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Protozoans Reproduction 

Binary fission is the most common form of asexual reproduction in the protozoans like amoebas and flagellates. Sometimes, the multiple asexual division will occur during protozoans’ asexual reproduction. Apicomplexa can undergo both sexual and asexual reproduction. During the binary fission reaction, the organelles of the individual will divide into two complete organisms. That division is transverse in the ciliates and longitudinal in the flagellates, but amoebas don’t have an apparent axis. Endodyogeny is also a kind of asexual division that occurs in toxoplasma and some other protozoa. During this process, two daughter cells forms within the parent cells and the wall ruptures to release smaller progeny. Apicomplexa & Schizogony commonly undergoes asexual division. Here, the nucleus is divided many times, and then the cytoplasm divides into smaller uninucleate merozoites.  Toxoplasma, Plasmodium, and other apicomplexans undergo the sexual cycle. During this process, they involve in fertilization to form the zygote, the production of gametes, encystation of the zygote to form an oocyst, and the formation of infective sporozoites (sporogony) within the oocyst.


Some protozoa require two different host species, they are having complex life cycles. But other protozoa required only a single host to complete their life cycle. That’s why a single infective protozoan entering a susceptible host can create an immense population inside the host.  But, the death of the host and the host’s defense mechanisms can limit the reproduction of the protozoans.  

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Nutritions of Protozoans

The nutrition of all protozoans is holozoic, which requires organic materials in the form of particles or solutions. Ameboas usually intake particulate food or droplets through a temporary mouth. It performs digestion and absorption through a food vacuole and ejects the waste substances. Many protozoans will have a permanent mouth in the form of cytosome or micropore. Through which they can intake the food and they are passed to food vacuoles. Pinocytosis is another method of ingesting nutrient materials. Here, they will intake fluids through a small temporary opening present in the body wall of protozoans. Further, the ingested nutritions will enclose within a membrane and forms a food vacuole. 

FAQs (Frequently Asked Questions)

Q1. What is Protozoology? 

Ans: The study of protozoans is termed protozoology. The Netherland scientist Antonie van Leeuwenhoek was the first person to observe sea protozoans under a simple microscope, which was constructed with simple lenses. Later, Antonie van Leeuwenhoek and his little animals are termed father of protozoology and bacteriology. He also made many discovered these disciplines. In between 1674 and 1716, he described the free-living protozoa, Giardia lamblia from his own stool and several parasitic species from animals. A person who was specialized in protozoology is known as protozoologists. Stanislaus von Prowazek was the one notable protozoologist. 

Q2. Why Do We Study Protozoans?

Ans: The protozoans play an important role in fertilizing soils. Usually, protozoa graze the soil bacteria and regulate the bacterial population in the soil. This helps to maintain them in a state of physiological youth in the soil. Some protozoans serve as a food source for Zooplankton. Protozoans act as the ultimate decomposers in the natural environment. 


The protozoans are classified into many types. They are Phylum Euglenida, Phylum Kinetoplastida, Phylum Ciliophora, Phylum Apicomplexa, Phylum Dinoflagellata, Phylum Stramenopila, Phylum Rhizopoda, Phylum Actinopoda, Phylum Granuloreticulosa, Phylum Diplomonodida, Phylum Parabasilida, and several other protozoans.