Physiology of protozoa

Organelles and their physiological role

Although protozoa are unicellular, their morphology includes highly specialized structures—organelles—that functionally replace the organs of multicellular animals.

• Locomotor apparatus. Movement in space is provided by various motor structures. Depending on the species, these can be temporary cytoplasmic protrusions (pseudopodia) or permanent structures—flagella and cilia.
• Nutrition system. The process of nutrient assimilation is carried out using digestive vacuoles, where enzymatic breakdown of the captured material takes place. Regarding energy and carbon acquisition, protozoa show diversity: both heterotrophs and autotrophs are encountered.
• Excretory system. To maintain osmotic pressure and remove metabolic products, contractile vacuoles function, periodically discharging their contents outside the cell.

Life cycle and reproduction

The life cycle of protozoa is highly complex and is often accompanied by a change in morphological forms of existence.

Most species are characterized by both asexual and sexual modes of reproduction, which can regularly alternate during development. A crucial physiological feature is the ability to encyst. A cyst is a resting form formed by the microorganism to successfully survive adverse environmental factors. In this state, metabolic processes slow down dramatically, and the cell becomes covered with a dense protective membrane.

Cultivation of pathogenic protozoa

The study of the physiology of parasitic infection causative agents (such as Entamoeba histolytica, Giardia, or Leishmania) requires their growth in laboratory conditions. Many of these pathogenic species are capable of multiplying on artificial culture media.

Mandatory requirements for media: For successful growth and division, cells require a rich nutrient substrate. A key and obligatory component of such artificial media is native proteins, as well as a set of amino acids.

In cases where microorganisms do not grow on standard media, microbiologists resort to alternative cultivation methods:

1. Inoculation of cell or tissue cultures.
2. Use of developing chicken embryos.
3. Administration of material to susceptible laboratory animals.

Class and exam questions

What else to study on this topic

• Mechanisms of formation and structure of digestive vacuoles
• The encystment process and factors triggering cyst formation
• Specific artificial media for the cultivation of Leishmania and Entamoeba histolytica
• Features of the alternation of sexual and asexual reproduction in parasitic species
• Technique of protozoan cultivation on cell cultures and chicken embryos

Other topics in the "Microbial Physiology" section

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