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Protist diversity

With the advent of DNA sequencing, the relationships among protist groups and between protist groups and other eukaryotes are beginning to become clearer. Many relationships that were based on morphological similarities are being replaced by new relationships based on genetic similarities. Protists that exhibit similar morphological features may have evolved analogous structures because of similar selective pressures—rather than because of recent common ancestry. This phenomenon is called convergent evolution. It is one reason why protist classification is so challenging. The emerging classification scheme groups the entire domain Eukaryota into six “supergroups” that contain all of the protists as well as animals, plants, and fungi ( [link] ); these include the Excavata    , Chromalveolata    , Rhizaria    , Archaeplastida    , Amoebozoa    , and Opisthokonta    . The supergroups are believed to be monophyletic; all organisms within each supergroup are believed to have evolved from a single common ancestor, and thus all members are most closely related to each other than to organisms outside that group. There is still evidence lacking for the monophyly of some groups.

The chart shows the relationships of the eukaryotic supergroups, which all arose from a common eukaryotic ancestor. The six groups are Excavata, Chromalveolata, Rhizaria, Archaeplastida, Amoebozoa, and Opisthokonta. Excavata includes the kingdoms diplomads, parabasalids, and euglenozoans. Chromalveola includes the kingdoms dinoflagellates, apicomplexans, and ciliates, all within the alveolate lineage, and the diatoms, golden algae, brown algae, and oomyctes, all within the stramenopile lineage. Rhizaria includes cercozoans, forams, and radiolarians. Archaeplastida includes red algae and two kingdoms of green algae, chlorophytes and charophytes, and land plants. Amoebozoa includes slime molds, gymnamoebas, and entamoebas. Opisthokonta includes nucleariids, fungi, choanoflagellates, and animals.
Protists appear in all six eukaryotic supergroups.

Human pathogens

Many 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. Other protist pathogens prey on plants, effecting massive destruction of food crops.

Plasmodium Species

Members of the genus Plasmodium must infect a mosquito and a vertebrate to complete their life cycle. In vertebrates, the parasite develops in liver cells and goes on to infect red blood cells, bursting from and destroying the blood cells with each asexual replication cycle ( [link] ). Of the four Plasmodium species known to infect humans, P . falciparum accounts for 50 percent of all malaria cases and is the primary cause of disease-related fatalities in tropical regions of the world. In 2010, it was estimated that malaria caused between 0.5 and 1 million deaths, mostly in African children. During the course of malaria, P . falciparum can infect and destroy more than one-half of a human’s circulating blood cells, leading to severe anemia. In response to waste products released as the parasites burst from infected blood cells, the host immune system mounts a massive inflammatory response with delirium-inducing fever episodes, as parasites destroy red blood cells, spilling parasite waste into the blood stream. P . falciparum is transmitted to humans by the African malaria mosquito, Anopheles gambiae . Techniques to kill, sterilize, or avoid exposure to this highly aggressive mosquito species are crucial to malaria control.

The light micrograph shows round red blood cells, each about 8 microns across, infected with ring-shaped P. falciparum.
This light micrograph shows a 100× magnification of red blood cells infected with P . falciparum (seen as purple). (credit: modification of work by Michael Zahniser; scale-bar data from Matt Russell)

Concept in action

This movie depicts the pathogenesis of Plasmodium falciparum , the causative agent of malaria.

Questions & Answers

Species A has 12 pairs of chromosomes and Species B has 11 pairs of chromosomes. Explain what occurs during mitosis and during meiosis in the hybrid that allows normal development and growth from zygote to adult, but causes the adults to be sterile.
Christina Reply
Why does water move through a membrane?
Christina Reply
How many bones are in the human skeleton
Treasure Reply
procce of digestion of proteins a long human alimentarycanal
Carson Reply
what are the properties of lipids?
Isiah Reply
They are: Fatty acids, fats, oils, waxes, phospholipid, glycolipids, steroids and some vitamins
explain why a fresh water fish excrete ammonia
Leonard Reply
plz answer my question
sorry i meant it has a nucleous unlike plant cells lol
Ammonia is the end product of protein catabolism and is stored in the body of the fish in high concentrations relative to basal excretion rates. Ammonia, if allowed to accumulate, is toxic and is converted to less toxic compounds or excreted
What are eukaryotic cells?
Nwosueke Reply
cell with no nucleous so not a plant cell
eukaryotic cells are membrane bound organelles that have a membrane bound nucleus
where does the cell get energy for active transport processes?
A'Kaysion Reply
IDK maybe glucose
what is synapsis
Adepoju Reply
how many turns are required to make a molecule of sucrose in Calvin cycle
Amina Reply
why Calvin cycle occurs in stroma
why do humans enhale oxygen and exhale carbondioxide?
Maryam Reply
why do humans enhale oxygen and exhale carbondioxide? For the purpose of breaking down the food
what is allele
uzoka Reply
process of protein synthesis
what is cell
Zulf Reply
a cell is a smallest basic, structural and functional unit of life that is capable of self replication
why does a fresh water fish excrete ammonia
plz answer my question
Ammonia is a toxic colorless gas and when its inside the fish biological system is converted to a less toxic compound then excreted in the form of urea. However too much ammonia will kill the fish " Ammonia Poisoning " which is a very common disease among fish.
what is cytoplasm
uzoka Reply
cytoplasm is fluid of cell.

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Source:  OpenStax, Concepts of biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11487/1.9
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