We explain what protozoa are, how they originated and their characteristics. In addition, its classification, reproduction and examples.

Most protozoa can be seen under a microscope.

What are protozoa?

It is called protozoa or protozoa to a set of microorganisms that are found in humid or aquatic environments, and that could be considered as microscopic animals. However, in some systems of biological classification they form their own kingdom called Protozoa; and in other cases they are part of the Protist kingdom, since they are considered the first evolutionary step of the eukaryotic beings, prior to the existence of animals, plants, mushrooms and algae that we know.

Traditionally, however, protozoa are considered primitive unicellular animals: hence their name, a union of the Greek words protos, "first", and zoo, "animal". This because they are heterotrophs (they must consume organic material) and are equipped with movement voluntary. There is currently scientific debate regarding its correct classification in the different branches of the tree of the life.

Most protozoa can be seen with a microscope, since their size ranges between 10 and 50 micrometers, and around 300,000 species of them are known, along the various rungs of the food chain microscopic: herbivores, decomposers, predators and parasites. Many of them are capable of infecting and making the human being.

Origin of protozoa

Protozoa are thought to be around 1.630 million years old on our planet, from their initial appearance in the Mesoproterozoic period. Its origin coincides with the emergence of the first eukaryotic cells, that is, with cell nucleus defined, and with the subsequent inauguration of a broad category of living creatures.

Various theories attempt to explain this passage from the simple and primitive world of prokaryotes that of eukaryotes, and one of the most accepted has to do with a process of endosymbiosis between two prokaryotic organisms. These first eukaryotic organisms were, precisely, the first protozoa of the history.

Characteristics of protozoa

Protozoa are unicellular organisms endowed with their own mobility.

Protozoa are an extremely diverse group, whose fundamental characteristics are:

  • Microscopic size and varied shape. Most protozoa are between 10 and 50 microns in size, but some species can grow to a millimeter or more. Their shapes, on the other hand, oscillate between amorphous (like amoeba) or elongated and oval (like paramecium).
  • They are single-celled organisms. Your body is all one cell, endowed with organelles and structures diverse, fulfilling nutritional, mobile, etc. functions.
  • They have their own mobility. And they travel through flagella, cilia or the elongation of their cytoplasms, as if they were "fingers".

Classification of protozoa

Flagellate protozoa have "tails" that aid in their movement.

The traditional classification of protozoa distinguishes between the following types:

  • Rhizopods. They are characterized by their displacement by pseudopods, that is, the formation of bulges in their cytoplasm and the plasma membrane, projecting them where you want to advance. These projections also serve to capture food and introduce it to the cytoplasm (phagocytosis), either by predating other organisms or assimilating organic material of waste.
  • Flagellated. Cells endowed with one or more flagella, which is the name of the "tails" with which they propel themselves forward in the environment.
  • Ciliates. Its plasma membrane is surrounded by cilia, that is, by smaller and more numerous filaments than flagella, which also serve to mobilize itself.
  • Sporozoans. Parasitic protozoa without much mobility, which have a phase of multiple division known as sporulation: a type of asexual reproduction which consists of producing spores or endospores, resistant structures that generate a new identical individual.

Reproduction of protozoa

Binary division consists of a cell dividing in two.

Protozoa can reproduce sexual Y asexually, depending on the environmental conditions and their life cycles. They tend to do so abundantly, which is key to their biological and evolutionary success. Its main methods of reproduction are:

  • Binary division (asexual). A process of cellular fission after mitosis (genetic replication), which consists of a cell dividing in two and generating new individuals identical to it and each other.
  • Gemmation (asexual). A protozoon it generates an identical copy of itself, within a resistant structure that remains with its parent and can even outlive it during difficult periods. Eventually, that structure (gem) is reactivated and brings back to life a specimen identical to the parent.
  • Sporulation (asexual). The original protozoan fragments into a set of spores or endospores, which support environmental changes and then give rise to entire individuals.
  • Cell fusion (sexual). Protozoa generate gametes or microgametes in their interior, which allow them to unite and form a zygote, mixing their genetic materials and obtaining in return a new individual of greater genetic variety, original. This process can be total or partial, and is usually carried out in periods of abundance of resources.

Diseases caused by protozoa

Amebiasis is an intestinal infection caused by pathogenic amoebae.

Some species of protozoa are harmful to humans and have adapted to parasitize the body, causing diseases such as:

  • Malaria.Also called "malaria", it is responsible for a genus of protozoa called plasmodium. Its symptoms are high fever, chills, sweating, headache, as well as nausea, cough, bloody stools, muscle aches, jaundice, and being aggravated by shock, kidney or liver damage and the death.
  • Amoebiasis This is a common intestinal infection, caused by the presence of pathogenic amoebae (there are free-living and non-pathogenic ones as well) in the intestine or digestive tract of a person. These protozoa cover the intestinal wall and make it difficult for nutrients to be absorbed, causing diarrhea of ​​varying degrees.
  • Toxoplasmosis Caused by protozoa of the genus toxoplasma, which are transmitted to humans through contact with infected cats and other types of felines, or with infected animal or human feces. Its symptoms are confused with those of the flu, but it also causes inflammation of the lymph nodes, spleen, liver and cysts in the tissues, being its greatest danger in pregnant women, since it affects the fetus causing malformations and other problems.

Examples of protozoa

Some common protozoa are:

  • Paramecium. A fast-moving, oval-shaped, ciliated, free-living protozoan.
  • Giardia. Parasitic protozoan that invades the human intestines, causing foul gas, inflammation and diarrhea.
  • Amoeba. A genus of predatory protozoa, which may or may not parasitize other multicellular living beings, or live freely in aquatic spaces.
  • Trichomona. Another genus of parasitic protozoa, which invade the vagina and are sexually transmitted, causing foul discharge, itching and painful urination, and even risk of premature labor.
!-- GDPR -->