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Protozoa characteristics

What are protozoa?

It is known as  protozoos  or  protozoa  to a set of microscopic organisms that inhabit humid environments or aquatic environments, which in some systems of biological classification form a kingdom of their own: Protozoa, which is considered as the first evolutionary step in the world of beings eukaryotes, previous to animals, plants, fungi and algae.



According to other classifications, more traditional, protozoa would be mostly unicellular and very primitive animals: they are heterotrophs (their metabolism depends on consuming organic matter) and are endowed with movement and reproductive capacity. However, these classifications are still open for debate.

Most protozoa can be seen with a microscope , since their size ranges between 10 and 50 micrometers. Approximately 300,000 species of them have been recorded, distributed in the different rungs of the food chain: herbivores, decomposers, predators and even parasites.

Characteristics of protozoa


  1. Origin of protozoa

It is estimated that protozoa have about 1630 million years on the earth, since the Mesoproterozoic period. Its evolutionary origin coincides with that of the first eukaryotic cell, that is, with a defined nucleus, and the inauguration of a whole category of living beings thereafter: eukaryotes.

There are various theories to explain this transition from the prokaryotic to the eukaryotic world, one of the most accepted being the symbiotic coexistence between an archaea and a parasitic cell, later symbiotic, which became a single and unique organism.

The appearance of the first unicellular organism endowed with cytoplasmic structures and external structures to mobilize represented a gigantic evolutionary leap in biological matter.

  1. Etymology

The name “protozoo” comes from the Greek  protos  (“first”) and  zoo  (“animal”), and was coined by George Goldfuss in 1818, to name what he supposed were the original animals. This type of living beings had already been observed by Leeuwenhoek in 1674, using self-made microscopes.

  1. Classification of protozoa

According to the traditional classification, protozoa can be of the following types:

  • Rizópodos . They are characterized by moving through pseudopods, that is, forming “fingers” with the cytoplasm and the plasma membrane that project forward. These projections are also used to capture food and introduce it to the cytoplasm, in a process called phagocytosis.
  • Ciliates . Its plasma membrane is surrounded by cilia, that is, similar filaments but smaller and numerous than the flagella, which serve to mobilize the cell.
  • Flagellates . They are endowed with one or more flagella, that is, “tails” that allow the cell to be driven and mobilized.
  • Sporozoans . These are parasites, lacking mobility but that have a multiple division phase known as sporulation, and that are causing diseases, such as malaria.
  1. Habitat

Protozoa require wet or directly aquatic means to survive, and this can occur under two conditions:

  • Protozoa of free life . Those that live in stagnant or residual waters, rivers or other natural spaces and are generally harmless to man, except in very specific conditions.
  • Pathogenic protozoa . Those that must infect or penetrate the bodies of more complex beings to fulfill their life cycle, and that make their habitat in, for example, in the intestines of man, in his blood, etc. In some cases they can also be diners, not just parasites.
  1. Reproduction of protozoa

Protozoa reproduce abundantly, a key condition for their biological and evolutionary success. This process can occur either sexually or asexually, depending on the conditions of the environment, through various processes:

  • Binary division (asexual) . The well-known “mitosis”, in which a cell divides into two and replicates itself.
  • Gemmation (asexual) . The protozoon generates a copy of itself in a resistant structure that stays close to itself and can survive during difficult periods, then reactivate and return to life a copy identical to the original.
  • Sporulation (asexual) . The original cell is fragmented into a set of spores, resistant to climatic changes, which will then give rise to entire individuals.
  • Meiosis (sexual) . The protozoa generate gametes or microgametes that allow forming a zygote joining the genetic material of two parents and thus obtaining a greater genetic richness, to then generate a new original individual. This process is usually carried out in periods of abundance of resources.
  1. Metabolism

Protozoa also breathe, except for a few that are capable of chemosynthesis or photosynthesis (usually considered  chromists ). In fact, their breathing is aerobic (requires oxygen) and they are particularly sensitive to the lack of this element.

  1. Feeding

As already said, they can be predators, herbivores or cellular detritóphagos, since they require the consumption of organic matter to be able to breathe and grow. In general, their “diet” consists of bacteria , other protists or microscopic waste from other processes.

  1. Structure

Protozoa are “naked” cells, with no cell wall or exoskeleton, which makes them very flexible and adaptable. They are usually unicellular, although there are cases of more complex, multicellular protozoa, but never get to compose a true organic tissue.

  1. Diseases caused by protozoa


Some protozoa are harmful to man and have adapted to the conditions of their body, thus being able to parasitize it and cause diseases, such as:

  • Malaria . Also known as malaria, it is caused by a group of parasitic protozoa of the genus  plasmodium , and is recognized by high fevers, chills, sweating, headache, and may also reach nausea, cough, bloody stools, muscle aches, jaundice, and aggravating with shock, kidney or liver damage and death.
  • Amebiasis . A common intestinal infection, due to the presence of pathogenic amoebae in the intestine or digestive tract, which “upholster” the intestinal wall, hindering the absorption of nutrients and causing diarrhea and other damages.
  • Toxoplasmosis . Caused by toxoplasma, a protozoan that is transmitted to humans in contact with cats and other types of infected cats, or in contact with infected animal or human feces. Its symptoms are disguised as flu, although it can also inflame the lymph nodes, the spleen, the liver and cysts in the tissues.
  1.  Examples of protozoa

Some common protozoa are: the amoeba (amoeba), the paramecium, the euglena, the blepharisma, the intestinal parasite Giardia or the famous  plasmodium  of malaria.



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