Animals that can only be seen with a microscope are the simplest. They form their kingdom, containing up to 40 thousand species. And although their number is so great, scientists only became acquainted with protist representatives in the 17th century thanks to the inventor of the microscope Anthony van Levenguk. In our article we will study their morphology, finding out how they differ among themselves and what is common in the structure of protozoa.
Biology on the role of unicellular animals in nature
According to systematics, this group of eukaryotic organisms includes representatives of the classes Sarkodovy, Sporoviki, Infusoria, and Flagellates. Having populated ecological niches in the hydro- and lithosphere, they became capable of various types of nutrition. Among the simplest there are autotrophs, for example euglena green, heterotrophs - ciliates, foraminifera and radiolarians, parasites such as malarial plasmodium or dysentery amoeba.
Most of them serve as the main food supply for multicellular animals: intestinal, arthropods, fish. Protozoa enter all trophic chains, playing the role of producers or consumers of the 1st order. Let's look at what is common in the structure of protozoa.
The cell as a whole organism
The body of the protist consists of a single cell and, although it does not have organs, tissues and systems, it is able to fully perform the functions of respiration, excretion, nutrition, and reproduction.
Externally, the animals are very different from each other, which is associated with the phenomenon of divergence. It arose as a result of natural selection and hereditary variation. Nevertheless, in the opinion of most scientists, all unicellular cells are descended from one ancient and extinct group of eukaryotic cells. This explains the similarity of their morphological plan. Consider what is common in the structure of protozoa, in more detail. For example, freshwater inhabitants: amoeba protea, ciliates, green euglena - have contractile vacuoles. They periodically throw out excess water and protect the animal from death by regulating the osmotic pressure of the fluid in the body.
Digestive vacuoles also have a similar structure, breaking down organic matter. The cells include the Golgi apparatus, mitochondria, and lysosomes. The above examples clearly show what is common in the structure of protozoa.
Flagellate class is characterized by intracellular structure similar to ciliates and amoeba. But in its composition it has species containing chloroplasts, such as, for example, green euglena. In the world, such protozoa are capable of photosynthesis - an autotrophic method of nutrition, like plants.
Cell membrane
Its composition and properties can be considered the criterion that is common in the structure of protozoa. The membrane consists of molecules of proteins and lipids and provides transport of substances, and glycocalyx is located above it. It contains signaling proteins and is responsible for irritability. In order for the body to be of a certain shape, a pellicle is formed, and in the sarcodes, a dense parietal layer of the cytoplasm. In marine rhizopods, the membrane on top is covered with a shell that performs a supporting function.
Despite the external differences of organisms due to adaptations to the environment, their cellular level of organization is a criterion that is common in the structure of protozoa.