DOCSLIB.ORG

Contribution of Electron Microscopy to the Study of Parasitic Protozoa

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Contribution of Electron Microscopy to the Study of Parasitic Protozoa Contribution of Electron Microscopy to the Study of Parasitic Protozoa W. de Souza Instituto de Biofisica Carlos Chagas Filho, UFRJj Rio de Janeiro, Brazil Tropical diseases represent a serious constraint on human development, imposing on 500 million people their heavy burden of sickness and incapacity, and killing some two millon people each year (World Health Organization,1995). Some of these tropical diseases are caused by parasitic protozoa which comprise a large number of species some of which are responsible for diseases with a high prevalence, such as (a) malaria, caused by members of the. genus Plasmodium, affecting about 500 millon people per year, (b) leishmaniasis, caused by members of the genus Leishmania, affecting about 16 millon people, (c) Chagas’ disease, caused by Trypanosoma cruzi, affecting about 14 millon people in Latin America, (d) sleepness disease, caused by members of the Trypanosoma brucei group, affecting about 3 millon people in Africa, (e) amebiais, caused by the anerobic protozoa Entamoeba histolytica, affecting about 16 millon people throughout the world. Some of these protozoa have a complex life cycle with developmental stages found in vertebrate and invertebrate hosts, as occur with Tcruzi and Leishmania. Others developed the ability to penetrate into mammalian cells, developing either in direct contact with cytoplasmic structures (T. cruzi) or within modified endocytic vacuoles of the host cell, known as parasitophorous vacuole ( Toxoplasma, Leishmania) . Still others only live in oxygen-poor media, as occur with Trichomonas, Entamoeba and Giardia. The analysis of the fine strucuture of these protozoa using several techniques associated with transmission electron microscopy revealed that some of them present organelles found in all eucaryotic cells, like mitochondria, peroxisomes, Golgi complex, etc. Others, do no present some of these structures. Still others show the presence of specialized organeles such as the kinetoplast and glycosome in protozoa of the Kinetoplastida order, and peripheral vesicle in Giardia. In addition they also present special cytoskeletal structures, such as the sub-pellicular microtubules and the paraflagellar rod in trypanosomatids, the axostyle and the costae in trichomonads. In this communication we will review some of the basic aspects of these structures. The kinetoplast is a compact array of extranuclear DNA associated with proteins, concentrated in the portion of the mitochondrion located close to the flagellar basal body. Is is formed by concatenated minicircles and peripheral maxicircles. Its morphology varies according to the parasite developmental stage. The glycosome is found in all members of the Kinetoplastida order. Usually it appears as a membrane bounded and rounded organelle with a homogenous matrix. In some species it may present an elongated form, as observed after three- dimensional reconstruction of the whole cell. Most of the time they are randomly distributed throughout the cell. Occasionally, however, they are closely associated to each other. In trypanosomatids which harbour an endosymbiont a close association between glycosomes and the ensosymbiont is observed. Biochemical studies have shown that most of the enzymes of the glycolytic pathway, which are usually localized in the cytosol of mammal cells, concentrate in the glycosome of trypanosomatids. These enzymes present a high pHi and can be localized in cells fixed in glutaraldehyde and incubated for a few hours in the presence of ethanolic phosphotungstic acid before embedding, a procedure usually employed to localize basic proteins. The glycosome is a specialized peroxisome. Cytochemical studies have shown the presence of catalase in the glycosome of some trypanosomatids. The peripheral vacuoles are found at the dorsal region of Giardia. Using different electrondense tracers we could show that macromolecules ingested via an endocytic process are localized in a few minutes in these vacuoles, remaining in these structures for several hours. In addition acid phosphatase, a well known marker of lysosomes, is also found in the vacuole, thus suggesting its lysosomal nature.Using three-dimensional reconstruction technique and electron tomography of cells incubated in cytochemical media for detection of acid phosphatase and glucose-6- phosphatase results were obtained suggesting that Giardia presents a primitive endo- lysosomal system in a single compartment. The cytoskeleton of trypanosomatids is mainly composed by sub-pellicular microtubulles arranged in a parallel array, running throughout the cell. They are localized below the plasma membrane and are connected to each other, as well as to profiles of the endoplasmic reticulum and the inner face of the plasma membrane, via small filamentous structures. The use of the quick freeze, freeze-tiacture, deep- etching and rotary replication technique revealed details of the cytoskeleton of trypanosomatids. No other cytoskeletal structures were found in the cytoplasm, except some filaments which connect the kinetoplast to the basal body. One characteristic feature of the flagellum of trypanosomatids is the presence of a complex array of filamentous structures, known as the paraflagellar or paraxial rod, located at the side of a typical axoneme. Thick and thin filaments were seen organized in a complex array. Special Y-shaped bridges connect the filaments to axonemal microtubules. This structure is not observed in trypanosomatids which harbour a cytoplasmic endosymbiont. The axostyle found in trichomonads is formed by a layer of microtubules associated to each other by filamentous bridges. The costae is a complex array of globular and filamentous proteins, which can be visualized in replicas of quick f&en, freeze- fractured and deep etched cells. Sunnorted bv PRONEX, FINEP. CNPa and FAPERJ .
Load more

Recommended publications
  • Base J Originally Found in Kinetoplastida Is Also a Minor Constituent of Nuclear DNA of Euglena Gracilis
    © 2000 Oxford University Press Nucleic Acids Research, 2000, Vol. 28, No. 16 3017–3021 Base J originally found in Kinetoplastida is also a minor constituent of nuclear DNA of Euglena gracilis Dennis Dooijes, Inês Chaves, Rudo Kieft, Anita Dirks-Mulder, William Martin1 and Piet Borst* Division of Molecular Biology and Centre for Biomedical Genetics, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands and 1Institute of Genetics, Technical University of Braunschweig, Spielmannstrasse 7, 38023 Braunschweig, Germany Received June 8, 2000; Accepted July 4, 2000 ABSTRACT DNA blots or by immunoprecipitation. The immunoprecipi- tated DNA can be analyzed by combined 32P-postlabeling and We have analyzed DNA of Euglena gracilis for the two-dimensional thin-layer chromatography (2D-TLC) experi- presence of the unusual minor base β-D-glucosyl- ments (6,7) to verify that J is present. Using these methods we hydroxymethyluracil or J, thus far only found in have shown that J is a conserved DNA modification in kineto- kinetoplastid flagellates and in Diplonema.Using plastid protozoans and is abundant in their telomeres (5). J was antibodies specific for J and post-labeling of DNA not detected in the animals, plants, or fungi tested, nor in a digests followed by two-dimensional thin-layer range of other simple eukaryotes, such as Plasmodium, chromatography of labeled nucleotides, we show Toxoplasma, Entamoeba, Trichomonas and Giardia (5). that ~0.2 mole percent of Euglena DNA consists of J, Outside the Kinetoplastida, J was only found in Diplonema,a an amount similar to that found in DNA of Trypano- small phagotrophic marine flagellate, in which we also soma brucei.
    [Show full text]
  • Download the Abstract Book
    1 Exploring the male-induced female reproduction of Schistosoma mansoni in a novel medium Jipeng Wang1, Rui Chen1, James Collins1 1) UT Southwestern Medical Center. Schistosomiasis is a neglected tropical disease caused by schistosome parasites that infect over 200 million people. The prodigious egg output of these parasites is the sole driver of pathology due to infection. Female schistosomes rely on continuous pairing with male worms to fuel the maturation of their reproductive organs, yet our understanding of their sexual reproduction is limited because egg production is not sustained for more than a few days in vitro. Here, we explore the process of male-stimulated female maturation in our newly developed ABC169 medium and demonstrate that physical contact with a male worm, and not insemination, is sufficient to induce female development and the production of viable parthenogenetic haploid embryos. By performing an RNAi screen for genes whose expression was enriched in the female reproductive organs, we identify a single nuclear hormone receptor that is required for differentiation and maturation of germ line stem cells in female gonad. Furthermore, we screen genes in non-reproductive tissues that maybe involved in mediating cell signaling during the male-female interplay and identify a transcription factor gli1 whose knockdown prevents male worms from inducing the female sexual maturation while having no effect on male:female pairing. Using RNA-seq, we characterize the gene expression changes of male worms after gli1 knockdown as well as the female transcriptomic changes after pairing with gli1-knockdown males. We are currently exploring the downstream genes of this transcription factor that may mediate the male stimulus associated with pairing.
    [Show full text]
  • Autophagy in Trypanosomatids
    Cells 2012, 1, 346-371; doi:10.3390/cells1030346 OPEN ACCESS cells ISSN 2073-4409 www.mdpi.com/journal/cells Review Autophagy in Trypanosomatids Ana Brennand 1,†, Eva Rico 2,†,‡ and Paul A. M. Michels 1,* 1 Research Unit for Tropical Diseases, de Duve Institute, Université catholique de Louvain, Avenue Hippocrate 74, postal box B1.74.01, B-1200 Brussels, Belgium; E-Mail: [email protected] 2 Department of Biochemistry and Molecular Biology, University Campus, University of Alcalá, Alcalá de Henares, Madrid, 28871, Spain; E-Mail: [email protected] † These authors contributed equally to this work. ‡ Present Address: Centre for Immunity, Infection and Evolution, Institute of Immunology and Infection Research, School of Biological Sciences, King’s Buildings, University of Edinburgh, West Mains Road, Edinburgh EH9 3JT, UK. * Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel.: +32-2-7647473; Fax: +32-2-7626853. Received: 28 June 2012; in revised form: 14 July 2012 / Accepted: 16 July 2012 / Published: 27 July 2012 Abstract: Autophagy is a ubiquitous eukaryotic process that also occurs in trypanosomatid parasites, protist organisms belonging to the supergroup Excavata, distinct from the supergroup Opistokontha that includes mammals and fungi. Half of the known yeast and mammalian AuTophaGy (ATG) proteins were detected in trypanosomatids, although with low sequence conservation. Trypanosomatids such as Trypanosoma brucei, Trypanosoma cruzi and Leishmania spp. are responsible for serious tropical diseases in humans. The parasites are transmitted by insects and, consequently, have a complicated life cycle during which they undergo dramatic morphological and metabolic transformations to adapt to the different environments.
    [Show full text]
  • The Intestinal Protozoa
    The Intestinal Protozoa A. Introduction 1. The Phylum Protozoa is classified into four major subdivisions according to the methods of locomotion and reproduction. a. The amoebae (Superclass Sarcodina, Class Rhizopodea move by means of pseudopodia and reproduce exclusively by asexual binary division. b. The flagellates (Superclass Mastigophora, Class Zoomasitgophorea) typically move by long, whiplike flagella and reproduce by binary fission. c. The ciliates (Subphylum Ciliophora, Class Ciliata) are propelled by rows of cilia that beat with a synchronized wavelike motion. d. The sporozoans (Subphylum Sporozoa) lack specialized organelles of motility but have a unique type of life cycle, alternating between sexual and asexual reproductive cycles (alternation of generations). e. Number of species - there are about 45,000 protozoan species; around 8000 are parasitic, and around 25 species are important to humans. 2. Diagnosis - must learn to differentiate between the harmless and the medically important. This is most often based upon the morphology of respective organisms. 3. Transmission - mostly person-to-person, via fecal-oral route; fecally contaminated food or water important (organisms remain viable for around 30 days in cool moist environment with few bacteria; other means of transmission include sexual, insects, animals (zoonoses). B. Structures 1. trophozoite - the motile vegetative stage; multiplies via binary fission; colonizes host. 2. cyst - the inactive, non-motile, infective stage; survives the environment due to the presence of a cyst wall. 3. nuclear structure - important in the identification of organisms and species differentiation. 4. diagnostic features a. size - helpful in identifying organisms; must have calibrated objectives on the microscope in order to measure accurately.
    [Show full text]
  • A KEY to the COMMON PARASITIC PROTOZOANS of NORTH AMERICAN FISHES Thomas L. Wellborn, Jr. and Wilmer A. Rogers Zoology-Ent
    . A KEY to the COMMON PARASITIC PROTOZOANS of NORTH AMERICAN FISHES Thomas L. Wellborn, Jr. and Wilmer A. Rogers Zoology-Entomology Department Series Fisheries No. 4 AGRICULTURAL EXPERIMENT STATION AUBURN UNIVERSITY E. V. Smith, Director March 1966 Auburn, Alabama (Revised June 1970) A KEY TO THE COMMON PARASITIC PROTOZOANS 1 OF NORTH AMERICAN FISHES Thomas L. Wellborn, Jr. 2/— and Wilmer A. Rogers 3/— Private, state, and federal fish husbandry industries suffer great losses each year because of disease and parasites. The parasitic protozoans included in this key are the ones most commonly associated with fish mortalities. A total of 23 genera of parasitic protozoans may be identified by use of this key. The fish protozoan parasites are responsible for a large part of the mortalities that occur at fish hatcheries each year. This is because they are capable of building up tremendous populations within relatively short periods of time, and some are capable of causing extreme damage to fish. Proper treatment and control of the diseases caused by the various protozoans are impossible without knowing their identity. This key will be helpful to fishery workers in identifying the more common genera. It must be remembered, however, that a microscope and knowledge of its use are absolute prerequisites for identifying protozoans. Certain parasitic protozoans cannot be identified below the rank of Order - without use of special techniques; therefore, all known genera are not included in the herein reported key. Protozoans belonging to such Orders should be sent to a specialist for identification. 1/ Supported in part by Southeastern Cooperative Fish Parasite and Disease Project (Fish Restoration Funds).
    [Show full text]
  • The Cytological Events and Molecular Control of Life Cycle Development of Trypanosoma Brucei in the Mammalian Bloodstream
    pathogens Review The Cytological Events and Molecular Control of Life Cycle Development of Trypanosoma brucei in the Mammalian Bloodstream Eleanor Silvester †, Kirsty R. McWilliam † and Keith R. Matthews * Institute for Immunology and Infection Research, Centre for Immunity, Infection and Evolution, School of Biological Sciences, King’s Buildings, University of Edinburgh, Charlotte Auerbach Road, Edinburgh EH9 3FL, UK; [email protected] (E.S.); [email protected] (K.R.McW.) * Correspondence: [email protected]; Tel.: +44-131-651-3639 † These authors contributed equally to this work. Received: 23 May 2017; Accepted: 22 June 2017; Published: 28 June 2017 Abstract: African trypanosomes cause devastating disease in sub-Saharan Africa in humans and livestock. The parasite lives extracellularly within the bloodstream of mammalian hosts and is transmitted by blood-feeding tsetse flies. In the blood, trypanosomes exhibit two developmental forms: the slender form and the stumpy form. The slender form proliferates in the bloodstream, establishes the parasite numbers and avoids host immunity through antigenic variation. The stumpy form, in contrast, is non-proliferative and is adapted for transmission. Here, we overview the features of slender and stumpy form parasites in terms of their cytological and molecular characteristics and discuss how these contribute to their distinct biological functions. Thereafter, we describe the technical developments that have enabled recent discoveries that uncover how the slender to stumpy transition is enacted in molecular terms. Finally, we highlight new understanding of how control of the balance between slender and stumpy form parasites interfaces with other components of the infection dynamic of trypanosomes in their mammalian hosts.
    [Show full text]
  • Novel Lineages of Oxymonad Flagellates from the Termite Porotermes Adamsoni (Stolotermitidae): the Genera Oxynympha and Termitim
    Protist, Vol. 170, 125683, December 2019 http://www.elsevier.de/protis Published online date 21 October 2019 ORIGINAL PAPER Novel Lineages of Oxymonad Flagellates from the Termite Porotermes adamsoni (Stolotermitidae): the Genera Oxynympha and Termitimonas a,1 b a c b,1 Renate Radek , Katja Meuser , Samet Altinay , Nathan Lo , and Andreas Brune a Evolutionary Biology, Institute for Biology/Zoology, Freie Universität Berlin, 14195 Berlin, Germany b Research Group Insect Gut Microbiology and Symbiosis, Max Planck Institute for Terrestrial Microbiology, 35043 Marburg, Germany c School of Life and Environmental Sciences, The University of Sydney, Sydney, NSW 2006, Australia Submitted January 21, 2019; Accepted October 9, 2019 Monitoring Editor: Alastair Simpson The symbiotic gut flagellates of lower termites form host-specific consortia composed of Parabasalia and Oxymonadida. The analysis of their coevolution with termites is hampered by a lack of informa- tion, particularly on the flagellates colonizing the basal host lineages. To date, there are no reports on the presence of oxymonads in termites of the family Stolotermitidae. We discovered three novel, deep-branching lineages of oxymonads in a member of this family, the damp-wood termite Porotermes adamsoni. One tiny species (6–10 ␮m), Termitimonas travisi, morphologically resembles members of the genus Monocercomonoides, but its SSU rRNA genes are highly dissimilar to recently published sequences of Polymastigidae from cockroaches and vertebrates. A second small species (9–13 ␮m), Oxynympha loricata, has a slight phylogenetic affinity to members of the Saccinobaculidae, which are found exclusively in wood-feeding cockroaches of the genus Cryptocercus, the closest relatives of termites, but shows a combination of morphological features that is unprecedented in any oxymonad family.
    [Show full text]
  • Kmcb-Abstract-Book-2019-Final
    VIII April 27 – May 1, 2019 2 Eight Kinetoplastid Molecular Cell Biology Meeting April 27 – May 1, 2019 Hosted by the Marine Biological Laboratory Woods Hole, Massachusetts, USA The meeting was founded by George A.M. Cross in 2005 Organizers George A.M. Cross 2005-2011 Christian Tschudi 2013-2019 3 KMCBM 2019 Acknowledgements The organizer wishes to thank: The Program Committee Barbara Burleigh (Harvard T. H. Chan School of Public Health, Boston, USA) James D. Bangs (University at Buffalo, Buffalo, USA) Stephen M. Beverley (Washington University School of Medicine, St. Louis, USA) Keith R. Matthews (The University of Edinburgh, Edinburgh, Scotland, UK) The Staff at MBL: Paul Anderson and the MBL Housing and Conference Staff for registration and housing; All the IT AV Support staff and the staff in Sodexo Food Service at the MBL. Cover Design: Markus Engstler 4 KMCBM 2019 Program Saturday, April 27 02:00 – 05:00 Arrival, Registration and Poster Session A setup 04:00 – 06:30 Greeting and Dinner 07:00 – 09:00 Session I: VSG (chair: Mark Carrington) 09:00 – 11:00 Mixer Sunday, April 28 07:00 – 08:30 Breakfast 08:45 – 11:45 Session II: Biochemistry/Metabolism (chair: Ken Stuart) 12:00 – 01:30 Lunch 02:00 – 04:30 Session III: Cell Biology (chair: Kimberly Paul) 06:00 – 07:00 Dinner 07:00 – 09:00 POSTER PRESENTATIONS: Session A 09:00 – 11:00 Mixer & Poster A/B Changeover Monday, April 29 07:00 – 08:30 Breakfast 08:45 – 11:45 Session IV: Pathogenesis I (chair: Luisa Figueiredo) 12:00 – 01:30 Lunch 01:30 – 06:00 Free Time 06:00 – 07:00 Dinner 07:00
    [Show full text]
  • Visceral Leishmaniasis (Kala-Azar): Caused by Leishmania Donovani
    تابع 2 أ.د / فاطمة إبراهيم سنبل أستاذ الميكروبيولوجيا الصيدلية • (Plate 2) • Life cycle of Balantidium coli Mastigophora • General characters : • This subphylum includes those protozoa that move actively by means of a Flagellum (or several flagella) during all or part of their life. In addition, the body has a definite form (not irregular as in amoebae) maintained by a firm pellicle on its outer surface. Some flagellates are devoid of a mouth opening but some have an opening or Cytostome through which food is ingested. They reproduced by longitudinal binary fission (not transverse fission as in case of B. coli). • Some have undulating membrane which appear to consist of highly modified flagellum. Flagellates have vesicular type of nucleus . • The parasitic flagellated protozoa fall into two categories with respect to the type of disease produced in humans : • a) Intestinal and genital flagellates : these are found only in the intestinal or genital tracts and their transmission does not require a biological vector and so pass directly from man to man usually enclosed in a cyst. They include : • - Giardia intestinalis (lamblia) • - Enteromonas hominis • - Trichomonas hominis • - Trichomonas tenax • - Trichomonas vaginalis • - Dientamoeba fragilis (amoeba-like flagellate) • The parasites are nearly all harmless commensals but two species, Giardia intestinalis and Trichomonas vaginalis are associated with inflammatory lesions in heavy infections and for practical purposes may be regarded as pathogenic . • b) Blood and tissue flagellates (haemoflagellates) : these infect the vascular system and various tissues and their transmission requires a biological vector. usually an arthropod (insect) in which they undergo a fresh cycle of alteration and multiplication before they can again infect man.
    [Show full text]
  • P1891 Trichomonas Vaginalis Lifecycle Revisited
    P1891 Trichomonas vaginalis lifecycle revisited Piotr Kochan1, Agata Pietrzyk2, Alban Vogel*3, Maria Gołębiowska3, Karan Kumar3, Eivind Krågebakk3, Andreas Talgø Lie3, Rebekka Nilsen3, Vilde Strøm3, Michael Zbiegien3, Barbara Papir4, Małgorzata Bulanda5 1Chair of Microbiology, Department of Bacteriology, Microbial Ecology and Parasitology, Kraków, Poland, 2Chair of Microbiology, Head of Parasitology Laboratory, Kraków, , 3School of Medicine in English, Jagiellonian University, Parasitology Research Circle, Kraków, Poland, 4Chair of Microbiology , Parasitology Laboratory, Kraków, , 5Jagiellonian University Medical College, Head of the Chair of Microbiology, Kraków, Poland Background: The World Health Organization (WHO) states there are 1 million new sexually transmitted infections (STI) occurring daily. Among these, Trichomonas vaginalis with over 140 million infected is ranked 4th, just after HBV with over 250 million infected, HPV with over 290 million and HSV ranked 1st with over 500 million infected. Despite the availability of treatment of this protozoan, it’s still prevalent both in the developing and developed countries, although chlamydial infections are on the rise, currently ranked as 5th by WHO. Trichomoniasis is twice as common as gonorrhea (~78 million), almost 4 times more common than HIV infections (~37 million) and 25 times more common than syphilis (~6 million). Trichomonas infection not only facilitates HIV acquisition due to epithelial damage, but also promotes HIV propagation. We aimed to re-evaluate our current knowledge on the lifecycle of Trichomonas vaginalis, including not only its multiplication, but also possible genetic exchange. Materials/methods: The study made use of two strains of Trichomonas vaginalis: reference strain ATCC-PRA-92 and the strain from the Chair of Microbiology of Jagiellonian University Medical College.
    [Show full text]
  • Cell & Molecular Biology
    BSC ZO- 102 B. Sc. I YEAR CELL & MOLECULAR BIOLOGY DEPARTMENT OF ZOOLOGY SCHOOL OF SCIENCES UTTARAKHAND OPEN UNIVERSITY BSCZO-102 Cell and Molecular Biology DEPARTMENT OF ZOOLOGY SCHOOL OF SCIENCES UTTARAKHAND OPEN UNIVERSITY Phone No. 05946-261122, 261123 Toll free No. 18001804025 Fax No. 05946-264232, E. mail [email protected] htpp://uou.ac.in Board of Studies and Programme Coordinator Board of Studies Prof. B.D.Joshi Prof. H.C.S.Bisht Retd.Prof. Department of Zoology Department of Zoology DSB Campus, Kumaun University, Gurukul Kangri, University Nainital Haridwar Prof. H.C.Tiwari Dr.N.N.Pandey Retd. Prof. & Principal Senior Scientist, Department of Zoology, Directorate of Coldwater Fisheries MB Govt.PG College (ICAR) Haldwani Nainital. Bhimtal (Nainital). Dr. Shyam S.Kunjwal Department of Zoology School of Sciences, Uttarakhand Open University Programme Coordinator Dr. Shyam S.Kunjwal Department of Zoology School of Sciences, Uttarakhand Open University Haldwani, Nainital Unit writing and Editing Editor Writer Dr.(Ms) Meenu Vats Dr.Mamtesh Kumari , Professor & Head Associate. Professor Department of Zoology, Department of Zoology DAV College,Sector-10 Govt. PG College Chandigarh-160011 Uttarkashi (Uttarakhand) Dr.Sunil Bhandari Asstt. Professor. Department of Zoology BGR Campus Pauri, HNB (Central University) Garhwal. Course Title and Code : Cell and Molecular Biology (BSCZO 102) ISBN : 978-93-85740-54-1 Copyright : Uttarakhand Open University Edition : 2017 Published By : Uttarakhand Open University, Haldwani, Nainital- 263139 Contents Course 1: Cell and Molecular Biology Course code: BSCZO102 Credit: 3 Unit Block and Unit title Page number Number Block 1 Cell Biology or Cytology 1-128 1 Cell Type : History and origin.
    [Show full text]
  • 23.3 Groups of Protists
    Chapter 23 | Protists 639 cysts that are a protective, resting stage. Depending on habitat of the species, the cysts may be particularly resistant to temperature extremes, desiccation, or low pH. This strategy allows certain protists to “wait out” stressors until their environment becomes more favorable for survival or until they are carried (such as by wind, water, or transport on a larger organism) to a different environment, because cysts exhibit virtually no cellular metabolism. Protist life cycles range from simple to extremely elaborate. Certain parasitic protists have complicated life cycles and must infect different host species at different developmental stages to complete their life cycle. Some protists are unicellular in the haploid form and multicellular in the diploid form, a strategy employed by animals. Other protists have multicellular stages in both haploid and diploid forms, a strategy called alternation of generations, analogous to that used by plants. Habitats Nearly all protists exist in some type of aquatic environment, including freshwater and marine environments, damp soil, and even snow. Several protist species are parasites that infect animals or plants. A few protist species live on dead organisms or their wastes, and contribute to their decay. 23.3 | Groups of Protists By the end of this section, you will be able to do the following: • Describe representative protist organisms from each of the six presently recognized supergroups of eukaryotes • Identify the evolutionary relationships of plants, animals, and fungi within the six presently recognized supergroups of eukaryotes • Identify defining features of protists in each of the six supergroups of eukaryotes. In the span of several decades, the Kingdom Protista has been disassembled because sequence analyses have revealed new genetic (and therefore evolutionary) relationships among these eukaryotes.
    [Show full text]