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Primitive Protista and ancient members of the Domain Archaea and Eubacteria (both prokaryotes) were the first living organisms to inhabit this planet circa 3.5 billion years ago. Organisms in the Domain Eukaryota evolved some time later, with the fossils of primitive protists dating back to the late Proterozoic era. Most biologists are in agreement that protists arose from primitive bacteria by way of more than one ancestral group. Various phyla of protists, therefore, represent separate evolutionary lineages or are polyphyletic in origin. Some protists are plant-like and are primarily autotrophic (they produce their own food), some are fungus-like and are absorptive heterotrophs. Ohters are animal-like and are heterotrophs themselves however they ingest their food. In this exercise, you will observe and study four phyla of animal-like protists. biologist, the animal-like Protists (those To an animal without chlorophyll), were described as protozoans (formerly a phylum designation). We will use this term to describe all unicellular, animal like protists, but it is important to realize that the term protozoa is not a taxonomic designation. The protozoa are most certainly descendant from those forms of life that gave rise to eumetazoans (multicellular organisms). Protists present today, however, have had a long evolutionary history and may be considerably different from their more primitive ancestors. It is therefore unreasonable to describe the protozoa as "primitive" as is commonly done. We describe protozoa as unicellular (cytoplasmic organization) as all functions are preformed with the limits of a single plasma membrane. Even though there are no tissues or organs in protists, there is a division of labor Amoeba protus within the organism not seen in more primitive bacteria. This division of labor within the organism are characterized by specific organelles. In addition, some protozoans may Currently taxonomists have described over 65,000 different protozoan species with over half of these organisms exant. These associate together to form colonies, and there may be extant Protozoa live in many different environments; they can drift in the ocean and are thedivision of labor among members of a colony. main components of zooplankton, creep across vegetation in fresh water rivers and ponds, crawl in deep soil, and even reproduce in the bodies of other organisms. All Protozoa can reproduce asexually, usually by binary fission. During binary fission, a protozoan divides into two genetically Identical Individuals. Some species reproduce by multiple fission, a form of cell division that results in a number of identical individuals. While ALL species can reproduce asexually, a few also reproduce sexually through conjugation. During conjugation, individuals from opposite mating strains pair and exchange genetic material. 1
CLASSIFICATION A Convenient way, but certainly not the only way to classify animal-like protists, is based on the way they move: 1. Phylum SARCODINA (SCARCODINIANS) are motile and move by extending their psuedopodia (extensions of their cytoplasm) or are planktonic and use ocean currents for locomotion. 2. Phylum ZOOMASTIGINA (ZOOFLAGELLATES) are also motile and propel themselves by means of a flagella. 3. Phylum CILIOPHORA (CILIAPHORANS) these cilliates are also motile and move by the uniform beating of their hair-like cillia. Phylum: SARCODINA (SAHR-kuh-DE-nuh) 4. Phylum APICOMPLEXA (SPOROZOANS) are sessile and do have an active means of Foraminfera Sarcodines include hundreds of propulsion Species of Amoebas, which inhabit fresh water, salt water, and soil. Some can even live on mud, rocks, and other surfaces in shallow, slow moving streams and ponds. Locomotion occurs when the lobes of cytoplasm extend, called --pseudopodia, which means "false foot", these form when endoplasm the inner portion of cytoplasm, pushes the ectoplasm, the outer layer, forward to create a blunt, armlike extension. Sarcodines also use pseudopodia for feeding. Sarcodines ingest bacteria and other protists, which they engulf by phagocytosis. Many Sarcodines have hard shells or a test, made of calcium carbonate or silica. These tests are common in foraminiferans and radiolarians. These tests will eventually sink to the bottom of the ocean making huge deposits of Amoeba sp. limestone called chalk.
Radiolaria
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Exercise Observe the representative organisms in the phylum Sarcodina using the 10x and 40x objectives on the microscope and note structures when possible. Amoeba sp. Identify the following structures: plasma plasmagel, plasmasol, vacuole, Radiolarians and Foraminiferans (common name) Not all amebas are naked. Some, including organisms including the protists representing these groups form tests. Observe the non-living portion of these Sarcodines, and identify these constituents of limestone and chalk beds. Some questions to ponder: Like many Sarcodines, leukocytes (white use blood amoeboid movement, do you think characteristic that has been
membrane, pseudopodia, nucleus, food contractile vacuole.
cells) also this is a evolutionarily conserved?
If a freshwater Sarcodine were placed in a low Phylum: Zoomastigina also known as salt solution, zooflagellates. <0.5% could it survive? What if it were place in a 5% These protists are animal-like flagellates, that is, solution? What would happen? flagellates who don't posess the abillity to do photosynthesis. This taxon is considered as Entameba histolytica is capable of forming outdated, because it is paraphyletic or even cysts, why would polyphyletic. Most have one or more whip-like this ability be important for this parasitic organelles called flagella, which are made up of protist? nine fused pairs of microtubles surrounding two central singlets. These flagella are far different then flagella observable in many bacterial species. Many species that represent this group Cross section of a Clamydomonas flagella at high magnification of protists Exercise are parasitic or act as symbionts. Observe Trypanosoma sp. using the 40x objective; note the size of the organism in comparison to neighboring erythrocytes. Also note the position of the parasite with respect to host cells. Also locate the nucleus and flagella. 3
1. Trypanosoma sp. This is a vertebrate parasite and it causes Sleeping sickness or African trypanosomiasis. Trypanosoma is transmitted by the tsetse fly, the disease it causes is endemic in certain regions of Africa, covering about 36 countries. It is estimated that 300,000 - 500,000 people are infected, and about 40,000 die every year. Many species in this genus also have the ability to undergo antigenic variation, a process in which the parasite evades the host's immune system by constantly modifying their surface membrane proteins.
Phylum: Apicomplexa Also known as Sprorozoans, all apicomplexans are animal parasites, and like Trypanosoma, can cause serious human disorders. Some species have multiple life cycles and can infect more then one host. In this lab we will look at Plasmodium falciparum, the causative agent of malaria. P. faciparum spreads throughout the human host as a tiny infectious cell called a sporozoite. The sporozoite has an complex of organelles located at the apical tip of the that contains enzymes used to perforate host hepatocytes. After development in the liver tissue the parasite is capable of infecting erythrocytes. Most Apicomplexans have an intricate life cycle with both sexual and asexual stages, and two different hosts. For example, P. falciparum, gametogenesis occurs in the cytoplasm of human erythrocytes, Exercise fertilization occurs in the gut of an Observe P. falciparum sporozoites using the 40x objective; note the position of the Anopheles mosquito. parasite within host cells. Some questions to ponder: How is this parasite different then Trypanosoma sp.? How are they similar? How could this disease (malaria) be controlled? 4
Phylum: Ciliophora
Paramecium sp. undergoing conjugation (left) and binary fission (right) [40x]
This is the largest, most complex, and most diverse group of protozoans. Ciliates occupy nearly all aquatic habitats, with some being symbiotic. As their name suggests, organism in this phyla have multiple cilia which the use for locomotion and feeding. Some ciliates may also have structures called trichocysts, which are specialized organelles capable of being discharged from the cell. Trichocysts may be used to anchor the organism, or to capture prey by paralyzing it with a poisoned tip. An interesting aspect of ciliates is their possession of two nuclei. One is called the micronucleus, and the other is known as the macronucleus. It is currently believed that the micronucleus is involved with sexual reproduction, while the macronucleus controls such aspects of the organism's life as growth, respiration, and asexual reproduction.
Paramecium sp. which is a common genus in this phyla, may reproduce asexually through binary fission, but they may also engage in a sharing of genetic information with another compatible paramecium through a process Stentor [40x] called conjugation. In this process, the two mating Exercise pairs of paramecia align their oral grooves and Observe Paramecium sp. using both the 10x and 40x objective. Compare slides swap mitotically produced DNA in displaying conjugation and binary fission. Survey the stentor slide and identify the form of multiple micronuclei, thus increasing the genetic nuclei and cilia. diversity for the next generation. Paramecium sp. Paramecium sp. [40x] Identify the following structures: plasma membrane, macronucleus, micronucleus, cilia, contractile vacuole, pellicle, oral groove. Some questions to ponder: What is conjugation? Is conjugation really a form of sexual reproduction, why or why not? The paramecium has an oral groove but no anus, why? What exactly is the function of the oral groove? 5