Lab Quiz 2 Study Guide

  1. Substrate: Starch
    Exoenzyme(s): ?
    Product(s): ?
    • Exoenzyme(s) and (Products):
    • Amylase and (Starch --> Dextrans --> Energy)
    • Maltase and (Maltose --> Glucose --> Glycolysis (energy))
  2. Substrate: Casein
    Exoenzyme(s): ?
    Product(s): ?
    • Exoenzyme(s) and (Products):
    • Caseinase and (Proteins --> Peptones --> Polypeptides --> Dipeptides --> Amino Acids)
  3. Substrate: Gelatin
    Exoenzyme(s): ?
    Product(s): ?
    • Exoenzyme(s) and (Products):
    • Gelatinase and (Proteins --> Amino Acids)
  4. A gelatin tube that is entirely solid after being refrigerated for 30 minutes:
    positive result because of solid, the reaction is a rapid gelatin hydrolysis
  5. A clear area around the bacterial growth appears on a skim milk plate:
    positive result because of clear area, positive caseinase
  6. Growth occurs on a starch plate. After iodine is added the agar surrounding the growth appears a blue-black color
    negative result because of blue-black color (starch+iodine), blue-black precipitation around growth = negative amylase or negative maltase
  7. Why a gelatin tube should not be shaken before refrigeration?
    Because mixing hydrolyzed gelatin with gelatin that hasn’t been broken down give us false negative.
  8. Why turbidity should be present in a fermentation tube that appears red before interpretation?
    Because it represent neutral pH 7 red color.
  9. Why, if two organisms are being tested on the same skim milk or starch plate, the streaks should be placed as far apart as possible?
    Because having enough room is very important for two organisms to show growth.
  10. A glucose fermentation tube is bright yellow in color and gas bubbles are seen in the Durham tube:
    Positive fermentation because of bright yellow which represents acid is produced and positive gas production which means bubble in Durham tube.
  11. A lactose fermentation tube is red in color and turbidity is present:
    Negative fermentation because of red which represents original and the presence of turbidity serves as control for growth.
  12. A surcose fermentation tube is bright yellow in color but has no visible gas bubbles within the Durham tube:
    Positive fermentation because of bright yellow which represents that acid was produced and negative gas production because of no visible gas bubbles within the Durham tube.
  13. When a fermentation tube color is yellow the pH is ________ while red color implies a pH that is _____.
    7, 6.8
  14. Why are negative results of morphological tests never useful in the identification of a bacterium?
    Negative results for morphological tests may be due to growth conditions rather than the organisms behavior (ex: no capsules may be due to growth conditions, not due to the organisms inability to form capsules.)
  15. What two characteristics of a microbe can be determined using a peptone iron deep?
    Agar deep: enhances anaerobic respiration and allows observation of motility.
  16. What does the formation of a black color along the bacterial growth indicate about the microbe?
    It indicates that the result is positive in H2S and motility.
  17. Name a genra or a family associated with IMViC:
  18. Interpret this: A urease tube appears deep pink.
    This means that this is positive (+) urease (alkaline).
  19. Explain what substance is produced by bacteria in the urease tubes to alter the color.
    The alkaline end product ammonia is produced by bacteria in the urease tube to alter the color.
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Lab Quiz 2 Study Guide
Study Guide