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Dr. W. Crone (303 FTZ, 629-7439, cronewil@hvcc.edu, www.hvcc.edu/academ/faculty/crone/index.html)

Text: Ch. 2, pp. 31-35; Ch. 16 9/13/99

possible web site: http://martin.parasitology.mcgill.ca/JIMSPAGE/WORLDOF.HTM

(The World of Parasites--a map of what you can expect to find in your travels!)

possible HVCC a/v source: VT 0440,"Conquest of the Parasites" (we'll see in class in Week 7)


PROTISTS: The organisms that we will discuss this week are 1) single-celled (or colonial) and 2) not members of the animal kingdom. Our understanding of the classification of living organisms continues to change: see Ch. 15. Looking at major nuclear differences, scientists now discuss the three major domains of

  1. Eucarya: eukaryotic organisms: animals, plants, fungi, etc.
  2. Bacteria: bacteria and their relatives (e.g., cyanobacteria, the blue-green algae)
  3. Archaea: bacteria-like organisms which tend to live in extreme environments, e.g., hot springs


In contrast, there are many"traditional" terms to help us organize our thoughts:

protists: simple, single-celled, colonial, or simply organized organisms made of eukaryotic cells with organelles and a membrane-bound nucleus.

  1. protozoans are more animal-like in that they eat.
  2. algae are more plant-like in that they photosynthesize.

animals: multi-celled, eukaryotic organisms that eat other organisms for nutrition.

plants: multi-celled, eukaryotic organisms with cell walls that synthesize their own food.

fungi: multi-celled, eukaryotic organisms with cell walls that absorb food for nutrition.

There are four major"kinds" (structural approaches) of single-celled protists:1,2


amoeba-like ones


with flagella, closely related to sarcodines


a general term for protozoans with a"spore-like" phase in their life cycle


have at least a band of cilia, if not fully covered with it


Given that these organisms are trying to fulfill all of life's functions at the single-cell stage, recognizing what is happening at membranes is important: to regulate passage of material, define inside from outside, define organelles, provide lots of surface area, separate cells, and act as receptor sites. What are some major ways to get across membranes?

  1. Simple diffusion or random movement in response to a concentration gradient, e.g., O2 from lungs to blood stream.
  2. Facilitated diffusion through protein channels or carrier molecules in the membrane, e.g., for amino acids after digestion.
  3. Osmosis, passage of water from area of higher concentration to one of lower concentration through a selectively permeable membrane, e.g., the contractile vacuoles seen in fresh-water protists.
  4. Filtration, a forcible filtering of small molecules through a membrane with (hydrostatic) water pressure, e.g., your kidneys.
  5. Active transport, requiring energy to take in materials against a concentration gradient, e.g., the potassium concentration in a cell much higher than that of the outside.
  6. Endocytosis, bulk movement of materials inward, e.g., an amoeba eating.
  7. Exocytosis, the packaging of materials for secretion, e.g., secreting of materials for the arthropod exoskeleton.

With their small size, diffusion is sufficient for protist respiration, excretion, and internal (intracellular) distribution of materials. Most protozoans do not make their own food, but eat such things as bacteria, food particles, or other protozoans. Most protozoa will multiply by fission, leading to two daughter cells, although sexual exchange of genetic material can occur, e.g., with the micronucleus of ciliates.

Phylum Sarcomastigophora ("fleshy whip bearing"): protists that have pseudopodia, flagella, or both; have a single type of nucleus.2 Flagella help to move through a fluid, but pseudopodia help to crawl on a surface.

Subphylum Sarcodina includes the sarcodines, or those with pseudopodia.

  1. Amoeba. The principle form of amoeboid movement is the pseudopodium ("false foot"). In lab you should see a difference between the clear ectoplasm on the outside and the granular endoplasm on the inside. The advancing end of the pseudopodium is called the hyaline cap. The endoplasm pours into the pseudopodium, reaching the hyaline cap, and converting to the stiffer ectoplasm. This acts as a sleeve in order to extend the pseudopodium. The process can be reverted easily.
  2. Disease-causing amoeba. Entamoeba histolytica is a world-wide cause of amebic dysentery, as it burrows into the walls of the large intestine and causes ulcers. Not all who carry it show symptoms.3 We will look at slides of Acanthamoeba in lab, a genus that can create severe corneal lesions for those patients with poor contact lens hygiene.3
  3. Radiolarians are marine amebae, with shells made out of silica. Foraminiferans are also marine, but with a shell of calcium carbonate. The shells of forams are full of"windows" through which pseudopodia poke out These incredibly common organisms make up a major portion of the marine plankton and sediment: the White Cliffs of Dover are made up of foram shells, for example.1

Subphylum Mastigophora: with flagella. The flagellates.

Class Phytomastigophorea: with chloroplasts, more plant-like.

  1. Euglena: Common in ponds, where they help to give a green tint to the water (from their chloroplasts). Flagellum is on the anterior end. Characteristic movement called euglenoid movement, with many changes in shape as the organism spirals along. A clear pellicle secreted by the ectoplasm helps with this shape change of the organism.
  2. Volvox: The name means"to roll" and you will see why in lab. A colonial flagellete with coordinated flagellar motion. Each individual cell has two flagella, a chloroplast, and is connected to the cells around it. Daughter colonies are a form of asexual reproduction.

Class Zoomastigophorea: without chloroplasts, more animal-like.

  1. Trypanosoma: A flagellate that causes sleeping sickness in Africa; spread through the bite of the tsetse fly. It has an undulating membrane or fold of plasma membrane along its length. Invasion of the central nervous system creates drowsiness and stupor before death.3
  2. Giardia lamblia: intestinal flagellate parasite that causes diarrhea, now widespread.
  3. Trichonympha: a flagellate of the termite gut that digests wood cellulose for the termite.1

Phylum Apicomplexa ("apical complex," a structure that helps with penetration of host cells): parasitic protists with complex life cycles. The sporozoans. From Class Sporozoea:

  1. Plasmodium: all sporozoans are internal parasites. There is usually an immature stage when the cell is enclosed in a resistant wall as a spore. The Anopheles mosquito bites a man, injecting Plasmodium (sporozoite stage) from its saliva into the blood stream. These then penetrate liver cells, undergo schizogeny or asexual cleavage multiplication, and produce merozoites, which then head to red blood cells. They form trophozoites (the ring stage) in there, and again multiply by fission to create more merozoites. When these break out of the rbcs, they cause the typical fever of malaria from the toxic byproducts of their metabolism. Eventually, some malaria cells mature and sexual gametocytes may be picked up by mosquito for next round. Sexual fusion occurs in the gut of the mosquito and those cells then travel to its salivary glands, ready to infect the next human.
  2. Toxoplasma gondii: another sporozoan that causes human disease. Pregnant women should stay away from cat feces.2

Phylum Ciliophora ("cilia bearing"): protists with cilia and well-developed feeding systems.

  1. Paramecium: Can be large and complex; some can be seen with the naked eye. Food is taken down an oral groove that ends in the cell mouth (cytostome). Food gets put into vacuoles and"paraded" around the organism before being dumped out a"anal pore" region. Two contractile vacuoles are quite noticeable to pump out water. As with other ciliates, Paramecium has a macronucleus for running the day to day stuff, and a micronucleus that is involved when the Paramecium becomes sexual.2 One should see spiral swimming movements, as its cilia beat in an orderly pattern. Trichocysts, in the ectoplasm deep to pellicle, can be released for defense.
  2. Vorticella: body of Vorticella is trumpet-shaped and the cilia are around the mouth. The macronucleus is long and curved. This body is on a thin stalk that can retract.
  3. Stentor. Like Vorticella in that its cilia surround the mouth, but Stentor's macronucleus is beaded and its body is not stalked.

1 R Buchsbaum, Animals Without Backbones, 3rd ed. (Univ of Chicago Press, Chicago, 1987), pp. 41, 50, 53.

2 CP Hickman et al., Biology of Animals, 7th ed. (WCB McGraw-Hill, Boston, 1998), pp. 365, 366, 375, 378.

3 WA Volk, JC Brown, Basic Microbiology, 8th ed. (Benjamin Cummings, Menlo Park, CA, 1997), pp. 571, 572, 616, 681.


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|03050: Invertebrate Zoology| |03051: Vertebrate Zoology| |03074: Economic Botany|


Please send comments and questions to: cronewil@hvcc.edu


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This page updated on September 15, 1999