Understanding Symbiosis: Definition, Types, and Examples

Symbiosis:

     Symbiosis refers to a  relationship between different organisms that provide mutual benefits. These relationships can be either temporary or permanent. There are three main types of symbiosis.

• Parasitism
• Mutualism
• Commensalism

Parasitism:

    It is relationship in which a parasite gains food and shelter while causing disease to the host. There are two main types of parasitism.

Ectoparasitism:

      The parasitism in which parasites live outside the body. For example: ticks, lice, leeches and mosquitoes.

Endoparasitism: 

     The parasitism in which parasites live inside the host's body. For example bacteria, viruses and tapeworm.   

 As  mentioned above, parasitism can be temporary or permanent.

  

Temporary parasite:

    The parasites which live their life cycle freely. They live on host for very short time. The common example of these parasites are leech, bedbugs and mosquito.

Permanent parasites:

     The parasites which live their complete life cycle on their host, they associate with host as a permanent part of life. These parasites cannot survive without their host. Examples of these parasites are intestinal viruses and bacteria.

Some plants also live as parasites. For example, the plant Cuscuta lives as a parasite on other plants. It has special roots called haustoria that wrap around the host plant and absorb or intake nutrients from vascular tissue(xylem and phloem)of the plant's cell.

Mutualism:

    An association between organisms in which both the host and the symbiont gain benefit without adverse effect. 

There are two types of mutualism.

Obligate Mutualism:

    An association in which organisms cannot live without each other. They are permanently linked and entirely depend on each other. For example, coral and an alga called zooxanthella form such a relationship. Zooxanthella provides food through photosynthesis, and the coral offers shelter.

Facultative Mutualism:

        In this association, organisms live freely and are not entirely dependent on each other for survival. They linked solely for mutual benefit. The common example is honeybees and flowering plant. Honeybees gain nectar as a food source, and in return, they help plants with pollination.

There are more general examples of mutualism.   

• An insect, the termite, lives on wood. Termite cannot digest wood on their own; there is a protozoan in their intestine. It secretes an enzyme called cellulase which helps in the digestion of wood. Both organisms obtain nutrients through their association.
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  Another example is nitrogen-fixing bacterium Rhizobium, which lives in the root nodules of plants such as beans and peas. This bacterium convert nitrogen into nitrates which plant intake for better growth. Rhizobium absorb nutrient from plant. It is beneficial for both.
• One the most common type of mutualism is mycorrhizae. It is association between vascular plant and certain fungi.
  
• Lichen is also a mutualistic association. It is relationship between a fungi and autotroph such as cyanobacteria and green algae. Fungal hyphae protect algae from direct strong sunlight and get food from algae. Lichen can grow everywhere, as land is fertile or harsh rocky. They are very important for ecosystem as bio-indicators of pollution. But some lichens are poisonous. 

Commensalism:

    It is association in which one organism gain benefit and without harming other organism. There are three types of commensalism which are:

Metabiosis:

    It is type of commensalism in which organisms gain benefits from byproduct of other organisms. In simple terms, one organism modifies its habitat and other organisms can survive easily in this habitat. For example, maggots(the larval stage of flies) develop on corpses(remains of dead bodies).

Inquilinism:

    Inquilinism is a type of commensalism in which organism live in the home of another organism or inside the body of animal without causing harm or providing help. For example, gophers live in hole in the ground, and many insects resides in these holes without causing harm or providing assistance. 

Phoresy:

     Phoresy derived from Greek word phorein, meaning "to carry", phoresy is a type of commensalism in which one organism uses another animal for transportation. For example, sucker fish attach to the shark for move to other locations.