protist

Examples of protist in the following topics:

• Cell Structure, Metabolism, and Motility

  • The cells of protists are among the most elaborate and diverse of all cells.
  • Many protist cells are multinucleated; in some species, the nuclei are different sizes and have distinct roles in protist cell function.
  • Protists exhibit many forms of nutrition and may be aerobic or anaerobic.
  • The majority of protists are motile, but different types of protists have evolved varied modes of movement .
  • Protists use various methods for transportation.

• Protists as Primary Producers, Food Sources, and Symbionts

  • Protists function as sources of food for organisms on land and sea.
  • Protists function in various ecological niches.
  • Protists are essential sources of nutrition for many other organisms.
  • In some cases, as in plankton, protists are consumed directly.
  • Protists do not only create food sources for sea-dwelling organisms.

• Protist Life Cycles and Habitats

  • Protist life cycles range from simple to extremely elaborate.
  • There are over 100,000 described living species of protists.
  • Paramecia are a common example of aquatic protists.
  • In addition to aquatic protists, several protist species are parasites that infect animals or plants and, therefore, live in their hosts.
  • Other protist species live on dead organisms or their wastes and contribute to their decay.

• Rhizaria

  • Rhizaria are a supergroup of protists, typically amoebas, that are characterized by the presence of needle-like pseudopodia.
  • Pseudopodia function to trap and engulf food particles and to direct movement in rhizarian protists.
  • The protist then transports its cytoplasm into the pseudopod, thereby moving the entire cell.
  • This type of motion, called cytoplasmic streaming, is used by several diverse groups of protists as a means of locomotion or as a method to distribute nutrients and oxygen.
  • Radiolarians display needle-like pseudopods that are supported by microtubules which radiate outward from the cell bodies of these protists and function to catch food particles.

• 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 fungus-like protist saprobes are specialized to absorb nutrients from non-living organic matter, such as dead organisms or their wastes.
  • Saprobic protists have the essential function of returning inorganic nutrients to the soil and water.
  • Describe the ways in which protists act as decomposers and the actions of parasitic protists on plants

• Archaeplastida

  • Archaeplastida are a supergroup of protists that comprise red and green algae, which include unicellular, multicellular, and colonial forms.
  • It is well documented that land plants evolved from a common ancestor of these protists; their closest relatives are found within this group.
  • Molecular evidence supports that all Archaeplastida are descendants of an endosymbiotic relationship between a heterotrophic protist and a cyanobacterium.
  • Other protists classified as red algae lack phycoerythrins and are parasites.
  • It is well supported that this group of protists share a relatively-recent common ancestors with land plants.

• Protists as Human Pathogens

  • Many protists exist as parasites that infect and cause diseases in their hosts.
  • 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.
  • However, T. brucei has thousands of possible antigens; with each subsequent generation, the protist switches to a glycoprotein coating of a different molecular structure.

• Early Eukaryotes

  • Protists are eukaryotes that first appeared approximately 2 billion years ago with the rise of atmospheric oxygen levels.
  • Others invade the cells of other protists, animals, and plants.
  • Not all protists are microscopic.
  • Some protists are multicellular, such as the red, green, and brown seaweeds.
  • It is among the protists that one finds the wealth of ways that organisms can grow.

• Pre-Cambrian Animal Life

  • Early animal life (Ediacaran biota) evolved from protists during the pre-Cambrian period, which is also known as the Ediacaran period.
  • It is believed that early animal life, termed Ediacaran biota, evolved from protists at this time.
  • Some protist species called choanoflagellates closely resemble the choanocyte cells in the simplest animals, sponges.

• Excavata

  • Many of the protist species classified into the supergroup Excavata are asymmetrical, single-celled organisms with a feeding groove "excavated" from one side.
  • Until recently, these protists were believed to lack mitochondria.
  • Whereas men rarely exhibit symptoms during an infection with this protist, infected women may become more susceptible to secondary infection with human immunodeficiency virus (HIV) or genital wart virus infection, which causes over 90% of cervical cancer.
  • The mammalian intestinal parasite Giardia lamblia, visualized here using scanning electron microscopy, is a waterborne protist that causes severe diarrhea when ingested.