parasitism

Examples of parasitism in the following topics:

• Symbiosis

  • In this relationship the parasite benefits, but the organism being fed upon, the host, is harmed.
  • The parasite, however, is unlikely to kill the host.
  • The parasite moves from species to species as it requires two hosts to complete its life cycle.
  • This diagram shows the life cycle of a pork tapeworm (Taenia solium), a human worm parasite.
  • Here, the parasite will absorb the nutrition from the host and continue to grow.

• Protists as Human Pathogens

  • Many protists exist as parasites that infect and cause diseases in their hosts.
  • Parasites live in or on an organism and harm that organism.
  • A significant number of protists are pathogenic parasites that must infect other organisms to survive and propagate.
  • Protist parasites include the causative agents of malaria, African sleeping sickness, and waterborne gastroenteritis in humans.
  • In response to waste products released as the parasites burst from infected blood cells, the host immune system mounts a massive inflammatory response with episodes of delirium-inducing fever as parasites lyse red blood cells, spilling parasitic waste into the bloodstream.

• Nutrients from Other Sources

  • A parasitic plant depends on its host for survival.
  • Some parasitic plants have no leaves.
  • The parasitic plant obtains water and nutrients through these connections.
  • The plant is a total parasite (a holoparasite) because it is completely dependent on its host.
  • There are about 4,100 species of parasitic plants.

• Excavata

  • This supergroup includes heterotrophic predators, photosynthetic species, and parasites.
  • Among the Excavata are the diplomonads, which include the intestinal parasite, Giardia lamblia .
  • Euglenozoans includes parasites, heterotrophs, autotrophs, and mixotrophs, ranging in size from 10 to 500 µm.
  • The human parasite, Trypanosoma brucei, belongs to a different subgroup of Euglenozoa, the kinetoplastids.
  • The parasite then travels to the insect salivary glands to be transmitted to another human or other mammal when the infected tsetse fly consumes another blood meal.

• Phylum Platyhelminthes

  • The Platyhelminthes are flatworms that lack a coelom; many are parasitic; all lack either a circulatory or respiratory system.
  • Many flatworms are parasitic, including important parasites of humans.
  • Parasitic forms feed on the tissues of their hosts.
  • The trematodes, or flukes, are internal parasites of mollusks and many other groups, including humans .
  • The cestodes, or tapeworms, are also internal parasites, mainly of vertebrates .

• Protists as Plant Pathogens

  • Many protists act as parasites that prey on plants or as decomposers that feed on dead organisms.
  • Protist parasites prey on terrestrial plants and include agents that cause massive destruction to food crops.
  • The oomycete Plasmopara viticola parasitizes grape plants, which causes a disease called downy mildew .
  • Describe the ways in which protists act as decomposers and the actions of parasitic protists on plants

• Root Modifications

  • Plants have a wide variety of roots for functions as diverse as structural support, food storage, and parasitism.
  • Epiphytic roots are a type of aerial root that enable a plant to grow on another plant in a non-parasitic manner.
  • Haustorial roots are often seen in parasitic plants such as mistletoe.

• Density-Dependent and Density-Independent Population Regulation

  • Most density-dependent factors, which are biological in nature (biotic), include predation, inter- and intraspecific competition, accumulation of waste, and diseases such as those caused by parasites.
  • An example of density-dependent regulation is shown with results from a study focusing on the giant intestinal roundworm (Ascaris lumbricoides), a parasite of humans and other mammals.
  • The data shows that denser populations of the parasite exhibit lower fecundity: they contained fewer eggs .

• Chytridiomycota: The Chytrids

  • Some species thrive as parasites on plants, insects, or amphibians, while others are saprobes.
  • An example of a harmful parasitic chytrid is Batrachochytrium dendrobatidis, which is known to cause skin disease .

• Protist Life Cycles and Habitats

  • Protists live in a wide variety of habitats, including most bodies of water, as parasites in both plants and animals, and on dead organisms.
  • Certain parasitic protists have complicated life cycles and must infect different host species at different developmental stages to complete their life cycle.
  • In addition to aquatic protists, several protist species are parasites that infect animals or plants and, therefore, live in their hosts.
  • Amoebas can be human parasites and can cause dysentery while inhabiting the small intestine.