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What are Parasites and Parasitism?
Certain organisms like protozoans, fungi, etc., infect the host (organism on which they survive) and use the host mechanism and metabolism to grow themselves.
Single-celled protozoans act as an infecting agent of diseases like malaria, sleeping sickness, animals like female anopheles mosquito, fungi like trichophyton, or plants such as mistletoe act like parasites on the host organism.
These parasites depend on the host’s metabolism for the food to survive; on the other hand, the host may not get any benefit from parasites and can even be dangerous for the host.
So based on dependence on the host, the parasites get divided into two categories: obligate parasites and facultative parasites.
Facultative Parasites
Parasites that are not dependent on the host for completing their life cycle are called facultative parasites; they can survive independently without the host; hence, they have their own metabolic mechanism and can reproduce without host machinery. So the presence of hosts for these parasites is not an essential factor. They live freely and infect the host rarely in their life span.
Examples of facultative parasites are candida, acanthamoeba, etc.
Certain fungi exist as facultative parasites but also as saprophytes when they are not infecting the host.
Obligate Parasite
Parasites that are dependent on the host for completing their life cycle are called obligate parasites; they cannot survive independently without the host, hence they do not have their own metabolic mechanism and cannot reproduce without the presence of host machinery. These parasites are also called holoparasites.
The host is an essential factor of the growth and development of obligate parasites as, without the host, both growth and development are hindered, the parasite may even die without the presence of a host.
Usually, they hurt the host and do not benefit the host; they may even kill the host.
Examples of obligate parasites are – rickettsia, taenia, etc.
Major distinguishing features in between obligate parasites and facultative parasites:
Parameters | Obligate parasites | Facultative parasites |
|---|---|---|
Definition | Parasites which are dependent on the host for completing their life cycle are called obligate parasites | Parasites which are not dependent on the host for completing their life cycle are called facultative parasites |
Dependence on host | they cannot survive independently without the host | They can survive independently even without the host |
Metabolic dependence | They do not have their own metabolic mechanism, without the host, their growth or development is stagnant or hindered | They have their own metabolic mechanism and can also reproduce without the presence of host machinery |
Reproduction | Obligate parasites Cannot reproduce without the absence of host | Facultative parasites can reproduce without the presence of a host |
Mode of transmission | Can infect another host from the primary host, and transmit directly | Cannot transmit directly from one host to another and have a synchronized life cycle for transmission |
Free living | Obligate parasite do not live freely, their growth and development is stagnant without the host | Facultative parasites can live freely, presence of host is not essential |
Life cycle | Life cycle is dependent on host, that makes the life cycle comparatively complicated | The life cycle is not dependent on the host, so independence makes its life cycle comparatively easier |
Examples | Examples of obligate parasites are – rickettsia, taenia | Examples of facultative parasites are candida, acanthamoeba |
Also See:
- Difference Between Plant Tissue and Animal Tissue
- Difference Between Non-statutory and Statutory Bodies
- Difference Between Exons and Introns
- Difference Between Endosmosis and Exosmosis
- Difference Between Inhalation and Exhalation
- Difference Between Ideal and Non-ideal Solution
Conclusion
Parasites infect the host for completing their life cycle; a parasite may be utterly dependent on the host for metabolic and reproductive activity, whereas a parasite may be free-living and infects the host at some intervals of time. Parasites which completely depend on the host are called obligate parasites, whereas those which can live freely are called facultative parasites. These two categories differ in terms of reproduction, dependence on the host, their metabolic activities and life cycle as a whole.
Obligates cannot complete the life cycle without the host. In contrast, facultative parasites can complete it, and they can live freely by different means and reproduce, facultative parasites necessarily do not infect the cell. In contrast, obligate parasites have to infect the cell for growth and development.
