There are unicellular animals and plants

Protozoa: A diverse group

What are unicellular organisms?

Protozoa are the simplest living things with a real cell nucleus; the genetic information is stored in it.

In addition, they have other elements that each have a special function: The endoplasmic reticulum and the Golgi apparatus, for example, are membrane systems that lie in the basic cell substance (cytoplasm); they are used to manufacture and transport various cell components. Energy is generated in the mitochondria, they are the cells' "power plants". A cell skeleton made of fine, criss-cross stretched, stretchable threads (filaments) keeps the body in shape or changes it. Many animal protozoa, also called protozoa, move with flagella or cilia that propel the animal forward by snaking, propeller-like circling or coordinated oar strokes.

Despite the simple basic plan, there are a large number of very different animal protozoa. The main groups are the flagellates (Flagellata), the rhizopods (Rhizopoda), the spore animals (Sporozoa) and the ciliate (Ciliata).

Are there unicellular organisms between animals and plants?

Yes. With the flagellates there are actually species that, like plants, carry chloroplasts and carry out photosynthesis, i.e. use sunlight to build up substance from carbon dioxide and water and generate energy. In the case of the green eye animal (Euglena viridis) an orange spot can be seen next to the point of attachment of the scourge at the front end: the eye animal owes its German name to it. The stain contains carotenoids and "shadows" a light-sensitive area at the end of the flagellum. In this way, Euglena can locate where the light is coming from. And depending on how intense it is, the whipping movement and swimming direction change: either towards the light source or away from it.

Euglena viridis is actually attributed to the plants, but there is a closely related species, Euglena gracilis, which loses its chloroplasts if kept in the dark, and another species, Astasia longawhich, due to a mutation, can no longer produce a green dye. Like other unicellular organisms, both feed on nutrients contained in water.

Can protozoa die of thirst?

Yes, they depend on moisture. Protozoa need fresh water, sea water, blood or other body fluids from other organisms to live. Many, however, are able to survive drought, cold, lack of food or oxygen by developing rest phases with resistant shells (cysts).

Can protozoa be dangerous to humans?

Yes, many unicellular organisms are parasitic. Among the flagellates and spore animals, for example, there are parasites that claim thousands of victims every year, especially in tropical and subtropical countries.

Some of the best known spore animals of this type belong Plasmodium vivax, Plasmodium malariae and Plasmodium falciparumwho have favourited Malaria Virus. They are transmitted by the bite of an infected female Anopheles mosquito, with which so-called sporozoites enter the human bloodstream.

These multiply asexually in several cycles in the vessel walls, liver cells and red blood cells and change shape in the process. Each cycle of reproduction ends in an attack of fever for the affected person. At the same time, gametocytes develop, i.e. cells that can form male or female sex cells. This only happens after the gametocytes have been ingested by another female Anopheles mosquito while sucking blood. Sexual reproduction of the malaria pathogen then takes place in their intestines: male and female sex cells combine to form the zygote. This migrates into the stomach wall of the mosquito and forms a cyst there, in which the sporozoites arise. When the cyst reaches a certain size, it will burst. The sporozoites are released and migrate to the salivary gland of the Anopheles mosquito in order to change hosts with the next bite.

Flagellates living as parasites can also go through complicated development cycles. In doing so, they change their shape several times - from rounded and flagellate to spindle-shaped with a free flagella or a flagella connected to the cell body via a membrane. In addition, they change location in their host, for example migrate from the blood into body cells; but they can also attack immune cells or the central nervous system - such as Trypanosoma brucei. This parasite, which is transmitted by the tsetse fly, triggers sleeping sickness, which is feared in large parts of Africa.

How do unicellular organisms reproduce?

Asexual or sexual. In the case of asexual (asexual) reproduction, a cell divides into two or more than one; here the parent and daughter generation are genetically the same. Before division, the nucleus of the "parent cell" has to double its chromosomes (mitosis) so that the "daughters" receive a normal set. In sexual (sexual) reproduction, the genetic material is united by two individual cells. So that the chromosome number of the individuals remains constant, a reduction division (meiosis) to the normal rate is necessary. In some protozoa there is a generation change: a generation with sexual reproduction is followed by a generation with asexual reproduction.