Micro - LAB test 1

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  1. what is the purpose of the oil immersion microscope?
    necessary to determine the morphology of prokaryotes
  2. which knob is used for focusing with the high power or oil immersion lens
    fine adjustment knob
  3. what is the highest magnification and which lens?
    • oil immersion
    • 1,000 (100x10)
  4. steps of performing aseptic technique while transferring bacteria and the reason for performing aseptic technique
    • Disinfect work area before and after
    • Pass bacterial test tube through flame x3 (before and after)
    • Flame needle or loop (before and after) be sure to let cool
    • Pass inoculation test tube through flame x3 (before and after)
  5. Reason for performing aseptic technique
    to alleviate contamination
  6. Purpose of Broth cultures?
    provide large numbers of bacteria in a small space and are easily transported
  7. Purpose of Agar Slants?
    provide a solid growth surface and are easier to store and transport than petri dishes
  8. Purpose of Agar Deep?
    used to grow bacteria that require less oxygen than is present on the surface of the medium
  9. Purpose of Semisolid deep?
    used to determine whether a bacterium is motile
  10. The steps needed to prepare slides for staining of bacteria (any staining)
    • Mark slides (circles) with wax pencil
    • Flame loop to sterilize
    • Uncap test tube and pass through flame x3
    • Get sample on loop from test tube and rub on slide
    • Flame loop to sterilize
    • Pass test tube though flame x3
    • Repeat for second sample
    • Allow slide to dry completely, then pas through flame x3 to set
    • Place drop of Crystal Blue on each sample for 30 seconds
    • Rinse with distilled water
    • Blot dry and then add other dyes, as necessary
  11. What is Complex media?
    media for which the exact chemical composition varies slightly from batch to batch
  12. What is Defined media?
    a medium in which the exact chemical composition is known
  13. Explain the reason why some cells stain positive and some negative in a gram stain
    Bacteria stain differently because of chemical and physical differences in their cell walls. Gram+ cell walls contain multiple layers of peptidoglycans and Gram- bacteria contain a thin layer…
  14. What is the Reason for using Crystal violet as a reagent?
    primary stain
  15. What is the reason for using Iodine solution as a reagent?
    fixes the violet the the cell wall for Gram+
  16. What is the reason for using Ethanol as a reagent?
    decolorizes sample in Gram- cells because the cell wall is thinner
  17. What is the reason for using Safranin as a reagent?
    dyes Gram- cells red to confirm
  18. What is the purpose of dilution?
    dilute the original sample to reduce the population of bacteria to a countable number
  19. Steps for Streak plate technique
    • Flame loop to sterilize
    • Uncap bacterial and pass tube through flame x3
    • Get sample on loop and spread onto one section of agar
    • Flame loop allow to cool
    • Spread sample on agar to second section
    • Flame loop allow to cool
    • Spread sample on agar to third section
    • Flame loop allow to cool
    • Spread sample on agar to fourth section not touching first section
  20. What is the purpose for counting bacteria and what is the formula?
    A plate with less than 25 colonies is too little and more than 250 colonies is too many. Colony forming units = number of colonies / dilution x amount plated
  21. Purpose of streak plate method?
    to isolate pure cultures
  22. Define Inoculate and purpose
    introduce bacteria to various forms of culture media to keep them alive and study their growth
  23. Define Contaminant
    unwanted microbes
  24. Define Aseptic technique and purpose
  25. Asepsis is the absence of bacteria, aseptic technique is used in microbiology to exclude contaminants
  26. Define Selective Medium and purpose
    suppresses growth of unwanted organisms and encourages the growth of desired microbes. Used to isolate or identify particular organisms.
  27. Define Differential Medium and purpose
    allows differentiation between colonies growing on the same plate. Used to isolate or identify particular organisms.
  28. Define Enrichment Medium and purpose
    contains chemicals that enhance the growth of desired bacteria. Used to support the growth of a particular organism, while inhibiting the growth of others
  29. Define Pellicle
    a membrane appearing on the surface of the nutrient agar where the bacteria is growing
  30. Define Nutrient Agar and purpose
    • an extract made from marine red algae
    • Purpose: cannot metabolize bacteria
  31. Define Mannitol Salt Agar and purpose
    • Pink (soft one)
    • Purpose: higher salt content is selective for staph as it ferments mannitol which produces acid. Acid turns one phenol red-yellow
  32. Define EMB Agar and purpose
    • (Purple one)
    • Purpose: inhibits Gram+ growth
  33. Simple dilution problem...
    • 1ml bacteria added to 9ml nutrient broth = 1:10
    • take 1ml of that dilution add to 9ml = 1:100… 
    • 10x10x10x10x10 = 1:100,000 
    • number of colonies on plate of 1:1000 dilution is 54,
    • then the count is 54 x 1000 = 54,000 bacteria/ml in sample
  34. The purpose of a starch plate
    tests the ability of an organism to produce certain exoenzymes that hydrolyze starch. The starch molecules are too large to enter the bacterial cell, so some bacteria secrete exoenzymes to degrade starch into subunits that can then be utilized by the organism.
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Micro - LAB test 1
Micro - LAB test 1
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