Organisms, whose body includes only one cell, belong to the simplest. They can have a different shape and all kinds of ways of movement. Everyone knows at least one name that the simplest living organism bears, but not everyone realizes that this is just such a creature. So, what are they, and what types are most common? And what are these beings? Like the most complex and coelenterates, unicellular organisms deserve detailed study.
Sub-kingdom of unicellulars
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 distinguished by a constant body shape, while others constantly change it. The main component of the body is the nucleus surrounded by cytoplasm. It contains several types of organelles. The first are cellular. These include ribosomes, mitochondria, the Galji apparatus, and the like. The second is special. These include the digestive and contractile vacuoles. Almost all the simplest unicellular organisms can, withoutparticular difficulty in moving. In this they are helped by pseudopods, flagella or cilia. A hallmark of organisms is phagocytosis, the ability to take in solid particles and digest them. Some can also carry out photosynthesis.
How do unicellular organisms spread?
Protozoa can be found everywhere - in fresh water, soil or sea. The ability to encyst provides them with a high degree of survival. This means that under unfavorable conditions, the body falls into a dormant stage, being covered with a dense protective shell. Creating a cyst contributes not only to survival, but also to spread - this way the organism can find itself in a more comfortable environment, where it will receive food and the opportunity to reproduce. Protozoa carry out the latter by dividing into two new cells. Some also have the ability to reproduce sexually, and there are species that combine both.
Ameba
It is worth listing the most common organisms. The simplest are often associated with this particular species - with amoebas. They do not have a permanent body shape, and instead use pseudopods for locomotion. With them, the amoeba captures food - algae, bacteria or other protozoa. Surrounding it with pseudopods, the body forms a digestive vacuole. From it, all the received substances enter the cytoplasm, and undigested is thrown out. The amoeba breathes through the whole body with the help of diffusion. Excess water is removed from the bodycontractile vacuole. The process of reproduction occurs with the help of nuclear division, after which two cells are obtained from one cell. Amoebas are freshwater. There are protozoa in the human and animal body, in which case they can lead to a variety of diseases or worsen the general condition.
Green Euglena
Another organism, common in fresh water, also belongs to the protozoa. Euglena green has a spindle-shaped body with a dense outer layer of cytoplasm. The front end of the body ends with a long flagellum, with the help of which the body moves. In the cytoplasm there are several oval chromatophores in which chlorophyll is located. This means that Euglena feeds autotrophically in the light - far from all organisms can do this. The simplest navigate with the help of an eye. If the euglena stays in the dark for a long time, chlorophyll will disappear and the body will switch to a heterotrophic mode of nutrition with the absorption of organic substances from the water. Like amoeba, these protozoa reproduce by fission and also breathe through their whole body.
Volvox
Among unicellular organisms there are also colonial organisms. The simplest, called Volvox, live just like that. 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. This is how volvox daughter colonies arise. The simplest ones differ in the same structure.algae known as chlamydomonas.
Infusoria shoe
This is another common inhabitant of fresh water. The name of ciliates is due to the shape of their 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 controls all life processes. Infusoria uses bacteria, algae and other single-celled organisms as food. The simplest often create a digestive vacuole; in shoes, it is located in a certain place at the mouth opening. Powder is present to remove undigested residues, and excretion is carried out using a contractile vacuole. Ciliates are characterized by asexual reproduction, but it can also be accompanied by the union of two individuals to exchange nuclear material. This process is called conjugation. Among all freshwater protozoa, the ciliate shoe is the most complex in its structure.
Single-celled in soil and sea water
In addition to the inhabitants of fresh water, it is worth listing other types of protozoa. So, in the sea, organisms of radiolarians and foraminifera are most often found. The dead bodies of the former form mineral deposits of opals and jasper. Foraminifera are distinguished by the presence of a shell of grains of sand or calcium, and after death they form lime or chalk. Both those and others are part of the plankton. A variety of protozoa also live in the soil. They play a significant role inthe formation of a new earth. In addition, organisms can be parasites. They lead to the most dangerous diseases of people and animals. The most famous is the malarial Plasmodium, which settles in human blood. Dysenteric amoebae can interfere with the functioning of the large intestine. Trypanosomes carry sleeping sickness.
