Every adult remembers from a school biology course what symbiosis is. Or at least heard that word. However, not everyone knows that the most common example of symbiosis is a couple of people - lactic acid bacteria. In fact, symbiosis is any form of relationship between two living organisms having a different genotype and origin, in which they coexist as a single system. However, symbiosis should not be confused with parasitism, as is often the case.
In nature, the following types of symbiosis exist: the aforementioned parasitism (a type of relationship useful to one partner and harmful to the other), mutualism (mutually beneficial relationship), commensalism (relationship useful for one partner and indifferent to the other), and amenismism (relationship harmful to one side and indifferent to the second). In addition, in modern science it is customary to distinguish symbiogenesis or endosymbiosis, which is intracellular symbiosis: one organism lives inside the cell of another. Organisms in symbiotic relationships are called symbionts.
In order to understand what symbiosis is, it is first 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 inside simple eukaryotic cells. Initially, they were characterized by a symbiosis of 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 entrenched.
All other types of symbiotic relationships are built on the same principle. The easiest way to imagine what is symbiosis, on the classic example of lichens. This type of relationship should be regarded as mutualism, since the fungus receives from the cyanobacteria the nutrients synthesized by the latter, and, in turn, creates favorable environmental conditions for bacteria that protect against drying out, ultraviolet radiation and other adverse environmental factors, and also makes possible the existence of on a substrate having an acidic pH.
Parasitism is also a type of symbiosis. All eukaryotic pathogens of infectious diseases, including fungal ones, are considered its classic example. In such relationships, the parasite lives in the host’s body and feeds on its resources. There are obligate (permanent) and optional (periodic) parasitism. The first include viruses, the second - lice, helminths and others.
An example of mutualism is the aforementioned pair of human-intestinal microflora.
In the framework of commensalism, it is customary to distinguish many subspecies: zoochoria (distribution of parts of plants that serve for reproduction, with the help of animals) - these are birds that feed on seeds or carry them on their feet), sinoykia (use by one organism of a house without harming the first, for example, fish laying eggs in mollusk shells). It should not be confused with Inquilism - using the owner’s dwelling with the destruction of the latter, for example, insects that set off larvae in mollusk shells or galls, while destroying the host’s body.
The most common example of amenalism is the relationship between the tree and the moss growing under it. Moss experiences a negative effect from such a symbiosis (lack of lighting, nutrients, water, etc.), and the tree is indifferent.
Thus, using fairly simple and vivid examples, it is easy to illustrate what symbiosis is and not to confuse mutualism with commensalism and parasitism.