Veritable powerhouses—even without DNA

Whether human beings or animals, plants or algae: the cells of most life forms contain special structures that are responsible for energy production. Referred to as mitochondria, they normally have their own genetic material, ...

Exotic signaling mechanism in pathogens

The unicellular parasite that causes sleeping sickness differs from other eukaryotes in the mode of regulation of an essential cellular signaling pathway. This provides a promising point of attack for drug development.

Expert discusses alternatives to pesticides

A researcher at the University of Arizona has discovered compounds derived from Photorhabdus, an insect pathogenic bacterium, that have antimicrobial and nematicidal properties that can potentially replace chemical pesticides.

Harnessing plant hormones for food security in Africa

Striga is a parasitic plant that threatens the food supply of 300 million people in sub-Saharan Africa.Scientists have found that they can take advantage of Striga's Achilles' Heel: if it can't find a host plant, it dies.The ...

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Parasitism

Parasitism is a type of symbiotic relationship between two different organisms where one organism, the parasite, takes favor from the host, sometimes for a prolonged time. In general, parasites are much smaller than their hosts, show a high degree of specialization for their mode of life, and reproduce more quickly and in greater numbers than their hosts. Classic examples of parasitism include interactions between vertebrate hosts and diverse animals such as tapeworms, flukes, the Plasmodium species, and scabs. Parasitism is differentiated from parasitoidism, a relationship in which the host is always killed by the parasite such as moths, butterflies, ants, flies and others.

The harm and benefit in parasitic interactions concern the biological fitness of the organisms involved. Parasites reduce host fitness in many ways, ranging from general or specialized pathology (such as castration), impairment of secondary sex characteristics, to the modification of host behaviour. Parasites increase their fitness by exploiting hosts for food, habitat and dispersal.

Although the concept of parasitism applies unambiguously to many cases in nature, it is best considered part of a continuum of types of interactions between species, rather than an exclusive category. Particular interactions between species may satisfy some but not all parts of the definition. In many cases, it is difficult to demonstrate that the host is harmed. In others, there may be no apparent specialization on the part of the parasite, or the interaction between the organisms may be short-lived. In medicine, only eukaryotic organisms are considered parasites, with the exclusion of bacteria and viruses. Some branches of biology, however, regard members of these groups as parasitic.[citation needed]

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