What is symbiosis: theory and classical examples

Every adult person remembers from the school course of biology what symbiosis is. Or, at least, I've heard that word. However, not everyone knows that the most common example of symbiosis is a pair of people - lactic acid bacteria. In fact, symbiosis is any form of relationship between two living organisms that have a different genotype and origin, in which they coexist as a single system. However, one should not confuse symbiosis with parasitism, as it often happens.

In nature, there are the following types of symbiosis: the aforementioned parasitism (a type of relationship useful to one partner and harmful to another), mutualism (mutually beneficial relationships), commensalism (relationships useful to one partner and indifferent to another), and amensalism (relationships harmful to one party and Indifferent to the second). In addition, in modern science it is customary to single out symbiogenesis or endosymbiosis, which is an intracellular symbiosis: one organism lives inside the cell of another. Organisms that are in symbiotic relationships are called symbionts.

In order to understand what symbiosis is, first of all it is necessary to consider its earliest form, namely symbiogenesis. Scientists have proved that the cellular organelles of mitochondria and plastids were previously separate ancient microorganisms: mitochondria were prokaryotic bacteria, and plastids were autotrophic bacteria that settled within the simplest eukaryotic cells. Initially, they were characterized by a symbiosis in the type of mutualism, that is, mutually beneficial relations. Then these organisms merged so much that they became a single structure, which eventually became genetically established.

By the same principle, all other types of symbiotic relationships are built. It is simplest to imagine what symbiosis is, on the classic example of lichens. This type of relationship should be considered as mutualism, since the fungus receives nutrients from cyanobacteria synthesized by the latter, and in turn creates favorable environmental conditions for bacteria, which protect against drying out, ultraviolet and other unfavorable environmental factors, and also makes possible the existence of On a substrate that has an acidic pH reaction.

Parasitism is also one of the types of symbiosis. A classic example of it are all eukaryotic pathogens of infectious diseases, including fungal ones. With such a relationship, the parasite lives in the host's body, feeds on its resources. There are obligate (permanent) and facultative (periodic) parasitism. The first include viruses, to the second - lice, helminths and others.

An example of mutualism is the above-mentioned man-intestinal microflora.

Within the framework of commensalism, it is customary to distinguish between a variety of subspecies: zoochoria (propagation of parts of plants that serve for reproduction, with the help of animals), such are birds that feed on seeds or carry them on their paws), sinoikia (using one organism of another's home without harming the first, Fish, laying eggs in shells of mollusks). It should not be confused with Inquilism - the use of a host's dwelling with the destruction of the latter, for example, insects, which unmask the larvae into the shells of mollusks or galls, while destroying the host's body.

The most common example of amensalism is the relationship between the tree and the moss that grows under it. Moss experiences a negative effect from such symbiosis (lack of lighting, nutrients, water, etc.), and the tree does not care.

Thus, with the help of fairly simple and vivid examples it is easy to illustrate what symbiosis is, and not to confuse mutualism with commensalism and parasitism.