Symbiosis is close co-living between two different organisms that in most cases both benefit from being in the relationship. The biological definition does not require mutual benefits, but in everyday language, we typically use the term when both organisms gain from the other. The co-living can be life-long (called obligatory symbiosis), or it can be for periods only (called facultative symbiosis).
A common form of symbiosis is between fungi and plants (primary producers), which forms mycorrhiza to exchange nutrients, water and energy. Another form is symbiosis between gut microorganisms and animals, especially large herbivores (plant eaters). The microorganisms use some of the herbivore’s food in the gut, but “in return” they improve the herbivore’s digestibility of it.
This creative view of gut bacteria was made with the aim of challenging the idea that a sterile world is desirable, and instead note that a flourishing bacterial community in the gut is beautiful. These images represent the fusion of science and artistic techniques to communicate this concept of ecology. Created by Dr Nicola Fawcett and Christopher Wood, CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0), via Wikimedia Commons).