What are protozoa?

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

  1. What are protozoa?

It is called protozoa to a set of microorganisms that are in humid or aquatic environments , and that could be considered as microscopic animals. However, in some biological classification systems 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 eukaryotic beings , prior to the existence of the animals , plants , fungi and algae that we know.

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

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

  1. Origin of the protozoa

It is thought that the protozoa have on our planet about 1.630 million years, since its initial appearance in the Mesoproterozoic period. Its origin coincides with the emergence of the first eukaryotic cells , that is, with a defined cell nucleus , and with the subsequent inauguration of a wide category of living beings .

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

  1. Characteristics of the protozoa

Protozoa - biology
Protozoa are unicellular organisms with their own mobility.

The protozoa are a very diverse group, whose fundamental characteristics are:

  • Microscopic size and varied shape. Mostly, protozoa measure between 10 and 50 micrometers, but some species can grow up to a millimeter or more. Their forms, however, oscillate between amorphous (like the amoeba) or elongated and oval (like the paramecium).
  • They are unicellular organisms. Your whole body is a single cell , endowed with diverse organelles and structures , which fulfill nutritional, mobile, etc. functions.
  • They have their own mobility. And they move through flagella, cilia or the lengthening of their cytoplasms , as if they were “fingers.”
  1. Classification of protozoa

Flagellated protozoa have “tails” that help 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 protrusions of their cytoplasm and plasma membrane , projecting them where they want to move. These projections also serve to capture food and introduce them to the cytoplasm (phagocytosis), either by predating other organisms or by assimilating organic waste material.
  • Flagellated Cells equipped with one or more flagella, which is the name of the “tails” with which they are driven forward in the environment .
  • Ciliates Its plasma membrane is surrounded by cilia, that is, smaller and numerous filaments than flagella, which also serve to mobilize.
  • Sporozoos. Parasitic protozoa and without much mobility, which have a multiple division phase known as sporulation: a type of asexual reproduction that consists of producing spores or endospores, resistant structures that generate a new identical individual.
  1. Protozoan reproduction

The binary division consists of a cell dividing in two.

Protozoa can reproduce sexually and asexually , depending on environmental conditions and their life cycles. They usually do it 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.
  • Budding (asexual) A protozoan generates an identical copy of itself, within a resistant structure that remains next to its parent and can even survive it during difficult periods. Eventually, that structure (gem) is reactivated and brings back to life a copy identical to the parent.
  • Sporulation (asexual). The original protozoan is fragmented into a set of spores or endospores, which support environmental changes and then give rise to entire individuals.
  • Cellular (sexual) fusion. Protozoa generate gametes or microgamets inside, which allow them to join 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.
  1. Diseases caused by protozoa

Diseases caused by it
Amebiasis is an intestinal infection caused by pathogenic amoebas.

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

  • Malaria. Also called “malaria,” a genus of protozoa called plasmodium is responsible for it . Its symptoms are high fevers, chills, sweating, headache, as well as nausea, cough, bloody stools, muscle aches, jaundice, and worsening with shock, kidney or liver damage and death .
  • Amoebiasis This is a common intestinal infection, caused by the presence of pathogenic amoebas (there are free-living and non-pathogenic ones too) in a person’s intestine or digestive tract. These protozoans cover the intestinal wall and hinder the absorption of nutrients, causing diarrhea of ​​varying degrees.
  • Toxoplasmosis Caused by protozoa of the genus toxoplasma , which are transmitted to humans through contact with cats and other types of infected 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 .
  1. Examples of protozoa

Some common protozoa are:

  • Paramecium . A ciliated protozoan of free life, oval and fast movement.
  • Giardia . Protozoan parasite that invades the human intestines, causing foul gases, inflammations and diarrhea.
  • Amoeba . A genus of predatory protozoa, which may or may not parasitize other multicellular living beings, or live in aquatic spaces freely.
  • Trichomonas . Another genus of parasitic protozoa, which invade the vagina and are transmitted sexually, causing foul secretions, itching and painful urination, and even risk of premature delivery.

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