Organisms whose body includes only one cell are among the simplest. They can have different shapes and all kinds of ways of movement. Everyone knows at least one name, which is the simplest living organism, but not everyone realizes that this is such a creature. So, what are they, and which species are the most common? And what kind of creatures are these? Like the most complex and intestinal, unicellular organisms deserve a detailed study.
Unicellular kingdom
Protozoa are the smallest creatures. Their bodies consist of one cell, which has all the functions necessary for life. So, the simplest unicellular organisms have a metabolism, are able to show irritability, move and multiply. Some are characterized by a constant body shape, while others are constantly changing it. The main component of the body is the nucleus surrounded by the cytoplasm. It contains several types of organelles. The first are all-cell. These include ribosomes, mitochondria, the Haljee apparatus, and the like. The second is special. These include digestive and contractile vacuoles. Almost all the simplest unicellular organisms can move around without too much difficulty. In this they are helped by pseudopods, flagella or cilia. A distinctive feature of organisms is phagocytosis - the ability to capture solid particles and digest them. Some may also carry out photosynthesis.
How are unicellular organisms distributed?
Protozoa can be found everywhere - in fresh water, soil or the sea. A high degree of survival is ensured by the ability to encyst. This means that under adverse conditions, the body falls into the resting stage, being covered with a dense protective shell. The creation of a cyst contributes not only to survival, but also to spread - so the body can be in a more comfortable environment, where it will receive food and the opportunity for reproduction. The simplest organisms carry out the latter by dividing into two new cells. Some also have the ability to reproduce sexually, there are species that combine both options.
Amoeba
It is worth listing the most common organisms. Protozoa are often associated with this species - with amoebas. They do not have a constant body shape, and pseudopods are used for movement. They amoeba captures food - algae, bacteria or other protozoa. Surrounding it with pseudopods, the body forms a digestive vacuole. From it, all the resulting substances enter the cytoplasm, and undigested is thrown out. The amoeba carries out the whole body through diffusion. Excess water from the body is excreted by the contractile vacuole. The process of reproduction occurs with the help of nuclear fission, after which two are obtained from one cell. Amoebas are freshwater. There are protozoa in humans and animals, in which case they can lead to a variety of diseases or worsen the general condition.
Euglena green
Another organism, common in fresh water, also belongs to the simplest. In euglena green, the body is spindle-shaped with a dense outer layer of the cytoplasm. The front end of the body ends with a long flagellum, with which the body moves. In the cytoplasm there are several oval chromatophores in which chlorophyll is located. This means that in the light of euglena it eats autotrophically - not all organisms can do this. The simplest are guided by the eye. If euglena stays in the dark for a long time, chlorophyll will disappear and the body will switch to a heterotrophic diet with the absorption of organic substances from water. Like amoeba, these protozoa multiply by division, and also breathe with their whole body.
Volvox
Among unicellular organisms, colonial organisms are also found. Protozoa called volvox live that way. They have a spherical shape and gelatinous bodies formed by individual members of the colony. Each volvox has two flagella. The coordinated movement of all cells provides movement in space. Some of them are capable of reproduction. So there are daughter colonies of volvox. The simplest algae, known as chlamydomonas, differ in the same structure.
Infusoria shoe
This is another common inhabitant of a freshwater reservoir. The name of the infusoria is due to the shape of its own cell, resembling a shoe. The organelles used for movement are called cilia. The body has a constant shape with a dense shell and two nuclei, small and large. The first is necessary for reproduction, and the second governs all life processes. The infusoria uses bacteria, algae, and other unicellular organisms as food. Protozoa often create a digestive vacuole, in shoes it is in a certain place at the mouth opening. Powder is present to remove undigested residues, and isolation is carried out using contractile vacuole. Ciliates are characterized by asexual reproduction, but it can be accompanied by the union of two individuals for the exchange of nuclear material. This process is called conjugation. Among all freshwater protozoa, the ciliates is the most complex in structure.
Unicellular in soil and sea water
In addition to the inhabitants of the freshwater reservoir, it is worth listing other types of protozoa. So, in the sea, the most common organisms are radiolarians and foraminifera. The dead bodies of the former form mineral deposits of opals and jasper. Foraminifera are distinguished by the presence of a shell of sand grains or calcium, and after death they form lime or chalk. Both those and others are part of plankton. A variety of protozoa also live in the soil. They play a significant role in the process of forming a new land. In addition, organisms can be parasites. They lead to the most dangerous diseases of people and animals. The most famous is malarial plasmodium, which settles in human blood. Dysenteric amoeba can disrupt the colon. Trypanosomes carry sleeping sickness.