Protozoa – Reproduction, diseases and characteristics

The protozoa are unicellular organisms, heterotrophs, eukaryotes, belonging to the group of protists. The term protist derives from the Greek and means “first of all”, reflecting the idea that they would have been the first eukaryotes to appear in the course of evolution.

This term was coined many years ago, when Protozoa was spoken within the animal kingdom. Currently, “protozoa” is used as a collective name, without taxonomic value.

These individuals can reproduce asexually or sexually and are organized into four phyla: sarcodina, mastigophora, ciliophora and sporozoa. They are found inhabiting the most diverse places, mainly humid environments, in fresh or salt water. They can cause several diseases, such as malaria, toxoplasmosis, giardiasis and others. Protozoa can parasitize some living beings, including man, causing illness .

Protozoa: general aspects

Protozoa are single-celled , which means that they have only a single cell and their size can vary between 2 and 1000 μm. Their survival is based on the absorption of nutrients from the external environment, as they do not have the capacity to synthesize organic matter from inorganic matter.

The protozoa are unicellular, that is, they are formed by only one cell (Photo: depositphotos)

The flexibility or stiffness existing in the body of these beings varies a lot according to their shape, depending exclusively on how their cytoskeleton appears, which is located just below what we call the cell membrane. The union of this membrane with this cytoskeleton results in what we call “film”, which is a type of body wall typical of this organism.


They are single-celled, heterotrophs, eukaryotes, some species can be parasitic on invertebrates and vertebrates or simply have free life.

What are they and where are they found?

The term protozoan is a collective designation for single-celled heterotrophic eukaryotes that obtain their food by ingestion or absorption. These organisms can be found in aquatic or humid environments.

How do they reproduce?

Reproduction can be asexual or sexual . Asexually by binary or multiple division / fission, where the nucleus divides into several parts and then the cell multiplies into several others, thus giving rise to new individuals. Sexually by conjugation and some species can also present the so-called alternation of generations.

How do they breathe?

Most protozoa have aerobic respiration , absorbing oxygen through a diffusion system, which depends a lot on environmental conditions. Some of these protozoa have the ability to form cysts, which contributed to their resumption of their original formation in conditions more favorable to breathing.

See also : Protista Kingdom


Among the various diseases caused by these beings we can highlight, for example: Trichomonas vaginalis , a parasite that is allocated in the vagina of women, causing trichomoniase. The Chagas disease that is transmitted through the feces of an insect called barber or chupança. Faeces are left in the vicinity where the insect stung its host, allowing the protozoan Trypanosoma cruzi to penetrate the bloodstream through the sting.

The malaria is also a disease caused by a protozoan of the genus Plasmodium, with three variations of the species (P. Vivax, P. Malariae and P. Falciparum). Such a disease affects millions of people worldwide, especially in tropical regions.

The toxoplasmosis is also caused by a protozoan parasite, toxoplasma gondii. Usually asymptomatic, but can cause blindness. Transmission occurs by eating cysts of the parasite in the cat’s feces or by eating raw or undercooked meat contaminated by the parasite.

Classification of protozoa

Phylum Sarcodina or Rhizopoda: heterotrophic protozoa that move or capture food by emitting pseudopods (pseudo = false; pruning = feet). This is the case for amebozoa and foraminifera. In amebozoa there are myxomycetes and amoebae. Myxomycetes are organisms that live in moist soils and on tree trunks. They feed on debris.

Amoebas can be found in fresh water, moist soil and seas. Some species are parasites, including humans. Foraminifers are especially marine organisms that live in sediment, although there are some species that live in suspension in water. They usually have an exoskeleton formed by calcium carbonate or by the agglutination of sand, sponges of sponges or other inorganic materials.

These organisms have left ample fossil record. Geologists use fossil foraminifera as indicators of where oil may be and also to assess climatic data from past geological eras, based on sea temperatures.

Phylum Mastigophora or Flagellata: (mastix = flagella; phoros = carrier), protozoa that move through flagella, as is the case with euglenophytes (there are non-chlorophyll forms in this group), trypanosomes, giardia, triconymphs, trichomonas, dinoflagellates (there are non-chlorophyll forms in this group).

As you can see, there are groups here that include chlorophyll and non-chlorophyll forms that have always been treated by both botanists and zoologists. Dinoflagellates are single-celled or colonial, they generally have two flagellae that are arranged in a characteristic way: one of them surrounds the cell, promoting its spin like a top and the other turns to the posterior region of the cell, causing it to move foward.

Among the dinoflagellates there are toxic representatives, such as Gonyaulax catenela and Gymnodinium breve, two species that can cause a phenomenon known as red tide. Under certain environmental conditions, intense proliferation of toxic organisms occurs, forming extensive patches of color usually reddish or yellowish on the sea surface, causing great mortality of fish and other marine animals.

See also :  Red tide – How does this phenomenon occur?

Phylum Ciliophora : heterotrophic protozoa that move or obtain food through cilia. Your lashes are also important in filtering food. They occur in fresh water, in the sea and in humid terrestrial environments. It is in this group that the greatest diversity of protozoan species is found. There are predatory representatives, others that feed on algae and there are also parasites and particulate filters. Example: Paramecium. The paramecium is a free-living protozoan, very common in ponds, ponds and freshwater pools.

Phylum Sporozoa: heterotrophic protozoa that do not have special structures for displacement, such as pseudopods, cilia and flagella, but can move in the middle by body flexions or sliding. They obtain food mainly by absorption or pinocytosis. This is the case of plasmodium, which causes malaria. They are also called apicomplexes, due to the presence of a structure called apical complex, related to the process of penetration or fixation of this parasite in the host cell.

by Abdullah Sam
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