Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Microscopy How to see the little ones How small are they? • Viruses - 50-100 nanometers • Bacteria - 1-5 micrometers • Eukaryotic cells - 10-100 micrometers Two major aspects of microscopy: Magnification and Resolution • Magnification - an ability to make objects appear larger, expressed as a number combined with X (times). • Example: A microscope magnifies a specimen by 100X. (This means the object looks 100 times as large as it really is). Two major aspects of microscopy: Magnification and Resolution • Resolution - the ability to show detail, to see magnified objects clearly. • Officially defined as the ability of an optical system to distinguish between two adjacent points. • Resolving power has to do with the wavelength of light employed for viewing, as well as other technical considerations. Two major aspects of microscopy: Magnification and Resolution • A good illustration of the relationship: “Even if a light microscope could be designed to magnify e.g. 10,000X, its resolving power COULD NOT be increased (due to the wavelength of visible light), and the enlarged image would be big but fuzzy”. The Compound Light Microscope (“Brightfield Microscopy”) • Two lenses: the ocular (10x) and the objectives (often 4x, 10x, 40x, and 100x) • Uses visible light • Maximum resolving power = 200 nanometers; maximum magnification = 2000X Cont'd • Specimens are usually stained since most microorganisms are clear; this increases the refractive indices of the specimen and the medium. Immersion oil • Immersion oil must be used under high magnification to reduce loss of light; the oil has a refractive index similar to the microscope slide. • Much better resolution Other types of microscopy • Darkfield microscopy - specimen appears light against a dark background (no staining necessary) • Fluorescence microscopy - specimens are stained with "fluorochromes", which absorb and reradiate UV light. The sample appears bright against a dark background. (Often used for diagnostic purposes with fluorescent antibodies) Electron microscopy • A beam of electrons is used instead of visible light • This allows much greater magnification and resolution • Electromagnets act as lenses to focus the beam Two types • Transmission electron microscopy • Beam penetrates sample just like in light microscopy. • Samples must be very thin! • Highest magnification and resolution (up to 1,000,000x, 1 nM) • Similar in idea to brightfield microscopy Scanning electron microscopy • Electrons bounce off the surface of the specimen, revealing a three-dimensional image. Deflected electrons are picked up by a detector. • Best pictures - magnifications typically 10,000x, res. 10 nM. • Similar in idea to darkfield microscopy Taxonomy • Taxonomy – The science of classifying organisms – Provides universal names for organisms – Provides a reference for identifying organisms Taxonomy • Systematics or phylogeny – The study of the evolutionary history of organisms • All Species Inventory (2001-2025) – To identify all species of life on Earth Taxonomy • 1735 Plant and Animal Kingdoms • 1857 Bacteria & fungi put in the Plant Kingdom • 1866 Kingdom Protista proposed for bacteria, protozoa, algae, & fungi • 1937 "Prokaryote" introduced for cells "without a nucleus" • 1961 Prokaryote defined as cells in which nucleoplasm is not surrounded by a nuclear membrane • 1959 Kingdom Fungi • 1968 Kingdom Prokaryotae proposed • 1978 Two types of prokaryotic cells found The Three-Domain System Table 10.1 The Three-Domain System Figure 10.1 Scientific Names Source of Genus Klebsiella pneumoniae name Honors Edwin Klebs Source of Specific epithet The disease Pfiesteria piscicida Honors Lois Pfiester Disease in fish Scientific binomial Salmonella Honors Daniel Salmon typhimurium Streptococcus pyogenes Chains of cells (strepto-) Penicillium notatum Tuftlike (penicill-) Trypanosoma cruzi Corkscrew-like (trypano-, borer; soma-body) Stupor (typh-) in mice (muri-) Forms pus (pyo-) Spores spread in wind (nota) Honors Oswaldo Cruz Taxonomic Hierarchy Figure 10.5 Species Definition • Eukaryotic species: – A group of closely related organisms that breed among themselves • Prokaryotic species: – A population of cells with similar characteristics – Clone: Population of cells derived from a single cell – Strain: Genetically different cells within a clone • Viral species: – Population of viruses with similar characteristics that occupies a particular ecological niche Domain Eukarya • Animalia: Multicellular; no cell walls; chemoheterotrophic • Plantae: Multicellular; cellulose cell walls; usually photoautotrophic • Fungi: Chemoheterotrophic; unicellular or multicellular; cell walls of chitin; develop from spores or hyphal fragments • Protista: A catchall for eukaryotic organisms that do not fit other kingdoms Prokaryotes