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Symbiosis Definition

What do you mean by symbiosis? A symbiosis definition suggests that it is a relationship where at least one species profits from the other. The relationship between the other species can be negative, positive, or neutral. Mutualism, commensalism, and parasitism are the three main categories of symbiosis.

Each symbiont, or community of organisms, have to be of a distinct species. Heinrich Anton de Bary described it in 1879 as "the coexistence of dissimilar species." A century-long controversy raged about whether the word should actually refer to mutualism, as in lichens. The restriction has now been lifted by biologists. 

Symbiosis can be either obligatory (whenever one or even more symbionts are completely reliant on one another for sustainability) or facultative (when they can lead their life independently).

Physical attachment is another way to describe symbiosis. Conjunctive symbiosis occurs when symbionts create a single body, whereas disjunctive symbiosis occurs when symbionts form separate bodies. Ectosymbiosis occurs when one person lives on the body of another, including head lice over human beings; endosymbiosis occurs when one partner resides within the tissues of someone else, for example, Symbiodinium inside the coral.

Physical Interaction

Symbiotic meaning: A symbiotic relationship wherein one symbiont resides inside the tissues of another, either intracellularly or extracellularly, is known as endosymbiosis.

Rhizobia, nitrogen-fixing bacteria which reside in root nodules along with legume roots; actinomycetes, nitrogen-fixing bacteria like Frankia that exist in alder root nodules; single-celled algae within reef-building corals; and bacterial endosymbionts which provide vital nutrients of approximately 10%–15% of insects are all representatives of diverse microbiomes.

Any symbiotic relationship wherein the symbiont resides on the host's body surface, such as the internal layer of the digestive tract or the ducts of exocrine glands, is known as ectosymbiosis. Ectoparasites like lice, commensal ectosymbionts like barnacles that stick themselves to the jaws of baleen whales, and also mutualist ectosymbionts including cleaner fish are examples of this.

We now know what is meant by symbiosis, let us look at the types of symbiosis.

Types of Symbiosis

Types of symbiotic relationships: 


Mutualism, also known as interspecies mutual altruism, is a long-term relationship amongst members of various species that benefits both parties. Mutualistic partnerships may be mandatory for both sexes, facultative for one but not the other (might be obligate for other), or facultative for both. Herbivores have quite a lot of mutualistic gut flora that support them in eating plant/organic material, that is harder to break down than animal prey. Throughout the intestines of herbivores, cellulose-digesting bacteria or protozoans make up the gut flora. Coral reefs are the product of a mutualistic relationship between coral species and the algae that reside within them. The majority of land and plant life and ecosystems depend on mutualism between plants and mycorrhizal fungi, which aid in the extraction of water and minerals from the earth.

The relationship between both the ocellaris clownfish and the tentacles of Ritteri sea anemones is an indicator of mutualism. The anemone is protected by the territorial fish against anemone-eating fish, and the anemone's stinging tentacles shield the clownfish against predators. The clownfish is protected from the stinging tentacles by a special mucus.


The host cell loses a few of the resources that the endosymbiont offers in endosymbiosis. As a consequence, the host encourages endosymbiont growth by developing specialised cells within itself. These cells modify the genetic makeup of the host in order to monitor the growing population of endosymbionts and guarantee which genetic changes are transmitted down the generations through vertical transmission (heredity).


Commensalism is a connection/relationship amongst two living beings in which one profit while the other is neither affected nor benefited significantly. It comes from the English term commensal, which refers to human social contact. It comes from the mediaeval Latin word com- (with) and mensa, which means "to share food." 

Commensal relationships can include one organism needing another for transportation (phoresy) or accommodation (inquilinism), or one organism using something produced by another after it has died (metabiosis). Hermit crabs use gastropod shells to cover their bodies, and spiders weave webs on plants are examples of metabiosis.


The parasite profits whereas the host is injured in a parasitic relationship. Endoparasites which reside inside the host's body, ectoparasites and parasitic castrators which exist on the host's surface and micro predators like mosquitoes that visit regularly, are all examples of parasitism.

Symbiosis parasitism is a very effective form of living; parasites make up approximately 40% of all species of animals, and the typical mammal hosts four nematodes, two cestodes, and two trematodes.


Mimicry is a kind of symbiosis where an organism pursues unique features of another species in order to change the dynamic of its connection with the mimicked organism for the sake of its benefit. Batesian and Müllerian mimicry are two forms of mimicry, the very first comprising one-sided manipulation and the other including mutual benefit. Batesian mimicry is a three-part exploitative interaction in which one animal, the mimic, has grown to imitate the other, the model, in order to manipulate a third, the dupe. The mimic and model has emerged to transmit a signal, while the dupe has grown to obtain it from the model, according to signalling theory.


Amensalism is an asymmetric relationship in which one species is damaged or destroyed by another while the other remains unaffected. Competition and antagonism are the two forms of amensalism. When a greater or stronger organism deprives a weaker or inferior one of a resource, this is known as a rivalry. 

When one entity is injured or destroyed by another via a chemical secretion, this is known as antagonism. A sapling growing in the shade of a mature tree would be an instance of rivalry. The mature tree will deprive the sapling of essential sunlight, and when it is big enough, it will absorb rainwater and reduce nutrients of the soil. The mature tree is not affected by the sapling in the whole process.

When a sapling dies, the mature tree benefits from the dying sapling's nutrients. Juglans nigra (black walnut), which secretes juglone, a substance that kills most herbaceous plants inside its root zone, is indeed an illustration of antagonism.

Define Symbiotic Nutrition.

Define symbiotic nutrition: Symbiotic feeding refers to a relationship wherein species share their shelter and food. This reciprocal partnership may or may not be advantageous to both parties.

Cleaning Symbiosis

Cleaning symbiosis is a relationship between two animals in which one (the cleaner) eliminates and consumes parasites as well as a few more substances from another's surface (the client). While it seems to be mutually beneficial, biologists have extensively discussed whether this is reciprocal selfishness or merely exploitative behaviour.

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FAQs on Symbiosis

1. What Role Does Symbiosis Play in Nature?

Ans. Symbiotic relationships are extremely significant in the ocean and in fact the whole of nature. Plants or animals of distinct species might become reliant on one another for existence in these kinds of relationships. They might share environments or ways of life, or they might communicate in a particular way to support the existence of some other organism.

2. What is the Major Difference Between Negative and Positive Symbiosis?

Ans. The major difference between negative and positive symbiosis is that positive symbiosis involves beneficial interactions/association whereas negative symbiosis tends to be unfavourable to harmful.

3. Give the Difference Between Symbiosis and Mutualism.

Ans. The major difference between symbiosis and mutualism is symbiosis is a close and long-term relationship amongst two organisms of different species whereas Mutualism defines relationships between members of similar or distinct species that are mutually beneficial. Mutualistic partnerships do not have to be symbiotic.