Protozoa Outline David Fan I.
Protozoa A. Introduction 1. According to the traditional five kingdom classication system, the Eukaryotic kingdom Protista consists of two major groups; protozoa and algae 2. Due to transitioning changes in protist classification, this outline will regard protozoa as an informal group encompassing eukaryotic unicellular or colonial organisms that lack true tissues, thus including both protozoa and algae. 3. Major difference: algae are photosynthetic, protozoa are heterotrophic 4. Though unicellular, they exhibit a wide variety of movements, feeding and behaviors 5. Most protozoan are free living and inhabit aquatic environments or moist soil, and only a few are pathogenic to humans 6. All can reproduce asexually and most can sexually B. Size 1. Average size of protozoan cell ranges from 10-200 micrometers, however some are as long as 0.16 inch (4mm) C. Cell Structure 1. No cell wall 2. Possess all eukaryotic structures except chloroplast 3. Cytoplasm consists of endoplasm and ectoplasm 4. The outer ectoplasm functions in feeding, mobility and protection 5. The endoplasm is the inner part of the cytoplasm that houses the nucleus and other organelles 6. Some protozoa have special structures for feeding, while others absorb food through their cell membrane 7. Motility is achieved through flagella, cilia and pseudopods 8. Structures called contractile vacuoles remove excess water from cell, especially in freshwater species D. Life Cycle 1. Includes trophozoite and cyst stages 2. The trophozoite or vegetative feeding form rounds up and becomes immobile if adequate nutrients and moisture aren’t available 3. A tough wall forms around the cell which becomes a dormant, resting structure called a cyst that persists until moisture and nutrient levels are sufficient 4. When conditions return to favorable, the cyst breaks open and releases an active trophozoite
5. Some protozoa are unable to form cysts and are less likely to survive changes in the environment E. Types of Protozoa 1. Tremendous diversity makes classification very difficult 2. Traditional approach groups protozoa by motility, instead of evolutionary history or relationships 3. Molecular data suggests that the evolutionary distance between some organisms grouped together based on motility mechanisms appears to be greater than the evolutionary distance between plants and animals F. Mastigophora (Flagellates) 1. The Mastigophora, or the flagellates, share the distinguishing characteristic of having one or more flagella. 2. Locomotion occurs when the flagella beat in an undulating motion, with a wave initiating at the junction of the cell body and the flagellum and traveling toward the end of the flagellum. 3. The flagella of some mastigophora are arranged in a unique pattern. 4. Flagellated protozoa that are sessile (non-motile) use their flagella to gather food, rather than to move from one location to another. 5. Since the system for grouping protozoa based on locomotory organelles is not phylogenetic (based on similarities), the flagellates actually consist of two vaguely distinct groups, the plantlike flagellates (Phytomastigophora) and the animal-like flagellates (Zoomastigophora). 1. Plantlike flagellates are considered algae because they have chloroplasts that carry out photosynthesis 6. Flagellates reproduce asexually by binary fission, in which a cell splits into two genetically identical, equally sized daughter cells, and some also reproduce sexually by syngamy, the fusion of two gametes 7. Most are free living, some are parasitic 8. Living inside flagellates are prokaryotic endosymbionts (organisms living inside another) that probably perform tasks such as nitrogen fixation, ammonium assimilation, and hydrogen metabolism F. Sarcodina (Amoebas) 1. Possess pseudopods (false foot) and cytoplasmic protrusions that function in locomotion and in gathering food 2. Some have blunt, cytoplasmic lobe-like pseudopods 3. Others have long, firm, needle-like projections supported by microtubules 4. Amoeba that are encased in a hard shell protrude their pseudopods through pores
5. The calcareous shells, or tests, from amoebas such as foraminifers and radiolarians form layers of chalk deposits in the ocean. 6. Moving: Extrudes pseudopodium from the cell body, anchors it to a surface, and then pulls the rest of the cell in that direction by contracting its body 7. When an amoeba senses nearby food such as bacteria, algal cells, or other protozoa, the pseudopodia reach around to envelope the particle, form a vacuole around it, and digest it into nutrients the organism can use. 8. Indigestible material leaves the cell by exocytosis. 9. Most are freeliving, but some are parasitic 10. Reproduce by binary fission, and can form cysts G. Siliophora 1. Includes protozoa such as paramecium that possess hundreds of cilia: short, dense, hairlike structures used for locomotion and feeding 2. Cilia usually occur in organized rows called kineties but also in tufts. 3. The cilia beat in a coordinated fashion to propel through the environment and to move food particles toward the mouth. 4. Most ciliates produce cysts, have a mouth, are harmless, and contain two types of nuclei: one large macronucleus and several micronuclei. 5. The macronucleus contains thousands of short pieces of DNA and is involved in regulation of the cell cycle. 6. The diploid (two sets of chromosomes) micronuclei contain two copies of each chromosome and divide by mitosis 7. Micronuclei are necessary for sexual reproduction by conjugation, a process during which individuals exchange genetic information but do not increase in numbers. 8. Ciliates reproduce asexually by binary fission. H. Apicomplexa 1. Parasitic 2. Contain no specialized locomotory structures, but sometimes move by creeping or bending 3. Used to be called Sporozoa because many members produce spores, but Apicomplexa is preferred since they all have specialized organelles that form an apical complex at their anterior end. 4. Microtubules extend from the apical complex to provide structural support for the cell, and enzymes produced in organelles of the complex assist in penetration of host tissues during infection. 5. have complicated life cycles that include both asexual and sexual stages and that involve at least one host species
6. Following sexual reproduction, apicomplexans form thick-walled zygotes called oocysts that undergo meiosis, giving rise to sporozoites, specialized sporelike cells that play a role in the transmission of infection. 7. Asexual reproduction occurs by repeated fissions to form many cells I. Pathogenic Protozoa 1. Relatively few protozoa are pathogenic but the ones that are affect millions of people a year 1. The four mentioned groups of protozoa all contain species that are pathogenic to humans or animals, but all of the members belonging to the phylum Apicomplexa are pathogenic 2. An infected individual can be asymptomatic, or have mild symptoms including diarrhea, stomach aches, and cramping. More severe cases are called ameobic dysentery and involve bloody stools, intense stomach pain, and fever 3. A person becomes infected by ingesting resistant cysts, which germinate upon entering the small intestine. 4. In the trophozoite stage, the amoebas migrate to the large intestine where they feed, grow, and divide. 5. The trophozoites can penetrate the intestinal lining and travel to the liver, lungs, or brain, but this is rare. 6. Some of the trophozoites in the intestine will form cysts that exit the body in feces 7. Treatment usually consists of prescribed antibiotics. Lack of sewage treatment facilities, improper treatment of sewage, and poor sanitation practices cause the spread of this disease. The cysts can persist in soil and water or on contaminated foods 8. Most affect digestive system 9. When the organism overgrows, gastroenteritis results. Symptoms include diarrhea, fatigue, bloating, cramping, and flatulence, caused when a thick layer of Giardia coats the lining of the small intestine and prevents nutrient absorption 10. Many people never show any symptoms and fight the infection without treatment, but some cases require antibiotics 11. Spread by direct or indirect contact 1. Oral-fecial, skin contact, contaminated objects, sex 2. Four different species of Plasmodium, belonging to the phylum Apicomplexa, cause malaria 3. After becoming infected, a person develops malaise, nausea, and sometimes diarrhea, followed by chills, fever, and sweating. These symptoms cycle every 48 to 72 hours. 4. Malaria causes anemia from lysis of red blood cells and leads to liver, spleen, and kidney damage resulting from the accumulation of cellular debris. In some types of malaria, vessels in the brain can become blocked, causing death.
5. The life cycle of Plasmodium is complex, involving an asexual stage carried out in a human host and a sexual stage in the Anopheles mosquito. 6. When a female Anopheles mosquito bites a human host, she injects an anticoagulant into the blood before sucking up her meal. 7. If the mosquito is carrying the protozoa, sporozoites are also injected. 8. The sporozoites enter the blood through a capillary and travel to the liver where they asexually reproduce to form thousands of merozoites (first stage) per cell. 9. After 5-16 days infected liver cells burst open, releasing the merozoites into the bloodstream. 10. The merozoites invade red blod cells, in which they develop into ring-shaped trophozoites and further asexual reproduction occurs, leading to the infection of more red blood cells 11. A pathologist can easily identify the ring-shaped trophozoites in a blood smear under the microscope. 12. Microgametocytes and macrogametocytes form from the merozoites, and persist in the person's bloodstream until another mosquito bites the human host. 13. While feeding, the mosquito ingests both types of gametocytes (eukaryotic germ cells), and inside the insect host the microgametocytes release spermlike gametes that fertilize the macrogametocytes, creating oocysts. 14. After multiple mitotic divisions, the oocysts release sporozoites that can infect another human host when the mosquito seeks its next blood meal. 15. The use of bed netting dipped in insecticide and the elimination of standing water where mosquitoes can breed are two effective preventative measures for the spread of malaria.