Structure of the PROTOZOA

Protozoa are included in the subkingdom protozoaand they are the most primitive organisms known within the eukaryotes. Most of them are unicellular and prokaryotic organisms, therefore, they are provided with a cytoplasm separated from the outside by a plasma membrane and a nucleus with a nuclear membrane.

In this lesson from a TEACHER we will talk about protozoa, focusing on the protozoa structure. If you are interested in knowing more about them, keep reading us!

The protozoa are organisms unicellular eukaryotes. There are free-living protozoa and parasitic protozoa of plants and animals. They are this type of protozoa, the parasites, the most studied in sciences such as Parasitology, for being the cause of parasitic diseases in humans.

The first parasite was discovered in 1674 in the gallbladder of a rabbit and is known as Eimeira stiedae. Nowadays, between 45,000 and 70,000 species are known and most are free-living, between 20,000 and 25,000 are fossils, while parasites are between 7,000 and 10,000. There are families like

Apicomplexa with all its parasitic members, while in others there are forms of free life and parasitic life.

Protozoa live in very diverse habitats. Free-living protozoa are usually found in water, soil, etc., and others may live in commensal or commensal relationships. symbiotic with other animals (for example, there are ciliated protozoa that live in the ruminant paunch without producing illness)

As a general rule, protozoa consist of a plasma membrane, the cytoplasm, the nucleus, and the organelles:

plasma membrane

The protozoa are surrounded by a plasma membrane that selectively regulates the entry and exit of molecules, acts as a signal receptor and protects and delimits it from the external environment.

In some parasitic protozoa, the outer part of the membrane is covered and protected in addition to an envelope of glycoproteins, glycolipids, and polysaccharides, known as glycocalyx,. In other protozoa, this glycocalyx acts as an antigen complex, allowing evasion of the host's immune response.

Under the electron microscope, the membrane is seen in the form of three layers, since the central lipid portion is electrolucent and the innermost and outermost layers are dense to the passage of electrons. In protozoa that form resistant forms such as cysts or oocysts, there is also a membrane cystic or resistance, formed by apposition of cytoplasmic materials to the membrane plasma.

Cytoplasm

The cytoplasm is part of the structure of protozoa. It is located under the plasma membrane and is made up of two parts:

• one that is within a system of endomembranes and that are the nucleus, the endoplasmic reticulum and the Golgi apparatus
• another substance that is external to this system of membranes or cytosol, formed by an aqueous liquid that contains proteins, enzymes and atoms.

In this structure is the cytoskeleton and organelles.

cytoskeleton and membrane organelles

The cytoskeleton is a kind of cellular skeleton that forms a framework and gives internal shape to cells and is made up of microtubules, microfibrils and intermediate filaments.

The organelles are the specialized structures in the different cellular functions and are surrounded by a membrane. Are:

• mitochondria: organelles present in aerobic protozoa and that provide the energy necessary for the biosynthetic and motor processes of the protozoa. They are surrounded by a double membrane and have internal ridges that increase the surface area and vary according to the needs of the species.
• lysosomes: they are organelles with acid hydrolytic enzymes that act in intra and extracellular digestion. They are divided into primary, secondary and residual bodies.
• vacuoles: they are permanent or transitory vesicles that have various functions, such as osmoregulation, contraction, digestion, excretion or the storage of substances.