Microscopy Overview and Techniques
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What is the function of the ocular lens in a compound light microscope?

  • It is responsible for the resolving power.
  • It magnifies by 20x.
  • It magnifies by 10x. (correct)
  • It serves as the lens closest to the specimen.
  • Which of the following is true regarding the resolution in microscopy?

  • Resolution allows us to distinguish two points that are closer together. (correct)
  • Resolution is not affected by the wavelength of light used.
  • Resolution decreases with shorter wavelengths.
  • Higher resolution means the ability to see at greater distances.
  • How is total magnification calculated in a compound microscope?

  • Ocular lens / Objective lens
  • Objective lens + Ocular lens
  • Ocular lens x Objective lens (correct)
  • Ocular lens + Objective lens - 1
  • What is a characteristic of an electron microscope compared to a light microscope?

    <p>Allows greater magnification, up to 500,000x.</p> Signup and view all the answers

    What type of electron microscope is used for examining internal structures of a specimen?

    <p>Transmission Electron Microscope (TEM)</p> Signup and view all the answers

    Which statement about light and resolution is accurate?

    <p>Resolution requires light to pass between two objects.</p> Signup and view all the answers

    What is the resolving power of a microscope if two points can be distinguished as long as they are at least 4 nm apart?

    <p>4 nm</p> Signup and view all the answers

    Why do samples prepared for a TEM often require staining with metal?

    <p>To enhance the contrast of internal structures.</p> Signup and view all the answers

    What defines a prokaryote?

    <p>Lacks membrane-enclosed organelles.</p> Signup and view all the answers

    Which shape describes a bacterium that is corkscrew-shaped?

    <p>Spirochete</p> Signup and view all the answers

    What is the function of capsules in bacteria like Streptococcus pneumoniae?

    <p>Protect against phagocytosis.</p> Signup and view all the answers

    What distinguishes a slime layer from a capsule in bacteria?

    <p>Capsules are organized and firmly attached to the cell wall.</p> Signup and view all the answers

    Which of the following eukaryotic organisms is classified as multicellular?

    <p>Fungi</p> Signup and view all the answers

    What type of organism typically possesses a single circular chromosome?

    <p>Archaea</p> Signup and view all the answers

    How do slime layers aid bacteria like Streptococcus mutans?

    <p>They promote biofilm formation.</p> Signup and view all the answers

    What is the primary characteristic of eukaryotes?

    <p>Have membrane-enclosed organelles.</p> Signup and view all the answers

    Which of the following is a characteristic feature of eukaryotic cells?

    <p>Presence of membrane-bound organelles</p> Signup and view all the answers

    What component of the cytoplasmic membrane provides rigidity compared to bacterial membranes?

    <p>Sterols</p> Signup and view all the answers

    Which type of eukaryotic cell wall component is found in fungi?

    <p>Chitin</p> Signup and view all the answers

    What is the primary function of mitochondria in eukaryotic cells?

    <p>Energy production</p> Signup and view all the answers

    What structural feature distinguishes eukaryotic ribosomes from prokaryotic ribosomes?

    <p>Size and weight</p> Signup and view all the answers

    What is the primary function of the bacterial cell wall?

    <p>To prevent rupture and protect against environmental changes</p> Signup and view all the answers

    Which of the following is NOT a function of the cytoskeleton in eukaryotic cells?

    <p>Protecting against pathogens</p> Signup and view all the answers

    Which of the following eukaryotic organelles is responsible for photosynthesis?

    <p>Chloroplasts</p> Signup and view all the answers

    Which macromolecule primarily composes the bacterial cell wall?

    <p>Peptidoglycan</p> Signup and view all the answers

    What function do flagella and cilia serve in eukaryotic cells?

    <p>Movement and motility</p> Signup and view all the answers

    Which of the following statements accurately describes Gram positive bacteria?

    <p>They have a thick peptidoglycan layer and only one membrane.</p> Signup and view all the answers

    What characterizes the outer membrane in Gram negative bacteria?

    <p>It is made of lipopolysaccharides, proteins, and lipids.</p> Signup and view all the answers

    What are the alternating monosaccharides that make up the polysaccharide portion of peptidoglycan?

    <p>N-acetyl glucosamine (NAG) and N-acetyl muramic acid (NAM)</p> Signup and view all the answers

    What type of acids are found in Gram positive bacteria that are not present in Gram negative bacteria?

    <p>Teichoic acids</p> Signup and view all the answers

    Which component of the Gram negative cell wall is known to be toxic?

    <p>Lipid portion of lipopolysaccharides</p> Signup and view all the answers

    What is a significant mechanism for distinguishing Gram negative bacteria such as E. coli?

    <p>The structure of their outer membrane and O-sugars</p> Signup and view all the answers

    What type of flagellar arrangement consists of a single polar flagellum?

    <p>Monotrichous</p> Signup and view all the answers

    Which of the following describes the motion produced by flagella when they turn in one direction?

    <p>Run</p> Signup and view all the answers

    What is the primary purpose of fimbriae in bacteria?

    <p>Adhesion to surfaces</p> Signup and view all the answers

    In which flagellar arrangement do tufts of flagella originate from opposite poles?

    <p>Amphitrichous</p> Signup and view all the answers

    Which statement accurately describes chemotaxis in bacteria?

    <p>It involves movement toward attractants and away from repellents.</p> Signup and view all the answers

    What is the function of pili in bacteria?

    <p>Genetic material transfer</p> Signup and view all the answers

    Which type of bacteria arrangement has flagella distributed all over the cell surface?

    <p>Peritrichous</p> Signup and view all the answers

    Which of the following best describes the structure of a flagellum?

    <p>Semi-rigid and helical</p> Signup and view all the answers

    Study Notes

    Microscopy

    • Light Microscope: Visible light is used to observe specimens
      • Compound light microscope: A type of light microscope that uses two lenses to magnify:
        • Ocular lens (Eyepiece): Magnifies by 10x.
        • Objective lens: Magnifies between 10x - 100x
    • Total magnification: Ocular lens x Objective lens
    • Resolution: Ability to distinguish fine detail.
      • Determined by the wavelength of light used, shorter wavelength, better resolution.
    • Electron Microscope: Uses electrons for viewing, higher resolution, higher magnification
      • Electron wavelengths are much shorter than light.
      • Magnification is much greater with this method (up to 500,000x).
      • Allows us to view viruses and internal cellular structures.
    • Types of Electron Microscope:
      • Transmission Electron Microscope (TEM): For visualizing internal structures, thin slices of the sample are required.
    • Prokaryotes:
      • "Before nucleus," DNA is not enclosed in a nucleus.
      • Usually have one circular chromosome.
      • Lack membrane-enclosed organelles.
      • Examples: Bacteria, Archaea.
    • Eukaryotes:
      • "True nucleus," DNA is located in the nucleus, surrounded by a nuclear membrane.
      • DNA is arranged in multiple chromosomes.
      • Contain membrane-enclosed organelles.
      • Examples: Algae, Protozoa, Fungi, Plants, Animals.

    Bacterial Morphology

    • Coccus: Spherical shape (plural: Cocci)
    • Bacillus: Rod-shaped (plural: Bacilli)
    • Vibrio: Curved shape
    • Spirillum: Spiral shape (plural: Spirilla)
    • Spirochete: Corkscrew shape.

    Bacterial Cell Structure

    • Capsule: Sticky gelatinous layer outside the cell, aids in protection from phagocytosis.
      • Examples: Streptococcus pneumoniae can cause disease when encapsulated, but not when lacking a capsule.
    • Slime layer: Unorganised and loosely attached, allows for surface adhesion.
      • Example: Streptococcus mutans can make polysaccharide slime from sucrose and attach to teeth, contributing to cavities.
    • Flagella: Long protein appendages used for motility.
      • Monotrichous: Single polar flagellum.
      • Lophotrichous: Two or more flagella originating from one pole.
      • Amphitrichous: Tufts of flagella originating from opposite poles.
      • Peritrichous: Flagella distributed all over the cell.
    • Fimbriae: Short hair-like appendages that allow the cells to adhere to surfaces.
      • They contribute to pathogenicity.
      • Example: Certain strains of E. coli can attach to the intestinal wall with fimbriae.
    • Pili: Allows attachment of two bacteria to each other, involved in genetic material transfer.
      • Example: E. coli sex pilus facilitates genetic exchange between bacteria.
    • Cell wall: Rigid structure defining the cell shape, prevents cell rupture, and protects from environmental changes.
      • Composed of peptidoglycan.
      • Used for bacterial identification.
      • Peptidoglycan: Composed of polysaccharide and amino acid chains, forming a mesh-like structure around the cell.
    • Gram positive cell wall: Thick layer of peptidoglycan outside the plasma membrane.
      • Contains teichoic acids:
        • Wall teichoic acids: Attached to the peptidoglycan.
        • Lipoteichoic acids: Attached to the plasma membrane and extend through the peptidoglycan.
      • Has only one membrane - the cytoplasmic membrane.
    • Gram negative cell wall: Thin layer of peptidoglycan sandwiched between two membranes.
      • Outer membrane composed of lipids (phospholipids), proteins, and lipopolysaccharides (LPS).
      • LPS contains O-sugars used for identifying Gram-negative bacteria.
      • The lipid portion of LPS is toxic and referred to as endotoxin.

    Eukaryotic cell structure

    • Includes a wide range of microorganisms: Algae, Fungi, Protozoa
    • Larger and more complex than prokaryotes
    • Cells contain a defined nucleus
    • Contains membrane-bound organelles
    • Cytoplasmic membrane: Similar structure to prokaryotic cells, composed of phospholipids, proteins, and sterols.
      • Sterols make the membrane more rigid compared to bacteria.
    • Cell wall: Not always present in eukaryotes, allows for endocytosis (taking in matter)
      • Simple structure, but different composition depending on the type of cell.
      • Made of cellulose (algae, plants), chitin (fungi).
    • Cytoplasm: The substance within the plasma membrane, outside of the nuclear membrane.
      • Contains the cytoskeleton - protein filaments that provide support, shape, and facilitate transport in the cell.
    • Ribosomes: Larger and heavier than bacterial ribosomes (80S).
    • Membrane-bound organelles: Structures with specialized functions, not found in bacteria.
      • Nucleus: Houses genetic material.
      • Mitochondria: Site of energy production.
      • Chloroplasts: Site of photosynthesis in algae and plant cells.
    • Flagellum and cilia: Long, flexible projections that contain protein and cytoplasm.
      • Used for motility and sweeping material past stationary cells.
    • Endocytosis: Process of bringing external matter into the cell.
    • Exocytosis: Process of releasing matter from the cell.

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