Microbio Chapter 7 Grace

Journal Questions and Answers

  1. Define growth? Describe how bacteria reproduce.
    Growth: Increase in the number of cells, not cell size.
    Reproduction: Bacteria reproduce through binary fission, budding, conidiospores, or fragmentation of filaments.

  2. What is generation time?
    Generation time: The time taken by bacteria to double in number.

  3. Draw the bacterial growth curve and describe what happens in each of the phases. Which phase is used for testing the effect of antibiotics?

    • Lag phase: Bacteria adapt to the environment; no significant growth.

    • Log (exponential) phase: Rapid cell division and growth; this phase is used for antibiotic testing.

    • Stationary phase: Nutrient depletion slows growth; equilibrium of growth and death.

    • Death phase: Cell death exceeds new growth.

  4. If you have 4 bacteria on a Petri dish, how many bacteria do you expect to have after 5 generations?
    Calculation: 4 × 2⁵ = 128 bacteria.

  5. How many hours will it take for the 4 bacteria to become 4096 in numbers? The generation time for the bacteria is about 30 minutes.
    Calculation:
    (log₂ 4096 / log₂ 2) × 30 mins = 6 hours.

  6. What are the physical requirements and chemical requirements for the bacteria?

    • Physical requirements: Temperature, pH, osmotic pressure.

    • Chemical requirements: Carbon, nitrogen, sulfur, phosphorus, oxygen.

  7. Classify the bacteria based on temperature requirement and what temperature range do you expect them to grow?

    • Psychrophiles: 0-15°C

    • Mesophiles: 25-40°C

    • Thermophiles: 50-60°C

    • Hyperthermophiles: >80°C

  8. Define minimum, optimum and maximum temperature with respect to growth

    • Minimum temperature: Lowest temperature for bacterial growth.

    • Optimum temperature: Best temperature for maximum growth rate.

    • Maximum temperature: Highest temperature at which bacteria can survive.

  9. Which bacteria grow in the refrigerator temperature? What is the optimum temperature for most types of bacteria?

    • Refrigerator bacteria: Psychrotrophs (0-20°C).

    • Optimum temperature for most bacteria: 25-40°C.

  10. Describe a practical application of extreme thermophiles
    Application: PCR (Polymerase Chain Reaction) uses Taq polymerase, an enzyme from the extreme thermophile Thermus aquaticus.

  11. What is the optimum pH for bacterial and mold growth?

  • Bacteria: pH 6.5-7.5

  • Molds and yeasts: pH 5-6

  1. What are acidophiles? Give examples
    Acidophiles: Bacteria that thrive in acidic environments.
    Example: Helicobacter pylori.

  2. Define obligate and facultative halophiles and give examples

  • Obligate halophiles: Require high salt concentrations for survival.

  • Facultative halophiles: Can tolerate high salt but do not require it.

  1. Describe what happens when bacteria are placed in hypotonic, hypertonic and isotonic solutions

  • Hypotonic solution: Water enters the cell, causing swelling.

  • Hypertonic solution: Water leaves the cell, causing plasmolysis (shrinkage).

  • Isotonic solution: No net water movement.

  1. Why do we preserve food in high concentration of salt or sugar?
    Reason: High salt/sugar creates a hypertonic environment, causing plasmolysis and inhibiting bacterial growth.

  2. Why did grandma ask you to gargle with salt water when you are suffering from throat infection? Is grandma a good microbiologist?
    Reason: Salt water creates a hypertonic environment, causing plasmolysis in bacteria, reducing infection.
    Conclusion: Yes, grandma understands microbiology!

  3. Why is condensed milk stored on the store shelf while 2% milk is refrigerated?

  • Condensed milk: Low water activity prevents bacterial growth.

  • 2% milk: Higher water content allows bacterial growth.

  1. Define osmotic pressure, osmolysis and plasmolysis

  • Osmotic pressure: Force exerted by water movement across a membrane.

  • Osmolysis: Cell bursts due to excessive water intake.

  • Plasmolysis: Cell shrinks due to water loss in a hypertonic solution.

  1. What are trace elements? Name some trace elements and why do bacteria require trace elements for growth?
    Trace elements: Inorganic elements required in small amounts, usually as enzyme cofactors.
    Examples: Iron (Fe), Zinc (Zn), Copper (Cu).

  2. Name the C, N, S and P sources for bacterial growth and what are these elements used for by the bacterium?

  • Carbon (C): Energy source, structural molecules.

  • Nitrogen (N): Amino acids, proteins, DNA.

  • Sulfur (S): Amino acids, vitamins.

  • Phosphorus (P): DNA, RNA, ATP.

  1. What are autotrophs and heterotrophs?

  • Autotrophs: Use CO₂ as a carbon source.

  • Heterotrophs: Obtain carbon from organic molecules.

  1. What are buffers? Name some substances in the media which can act as buffers?
    Buffers: Substances that maintain a stable pH in a medium.
    Examples: Phosphate buffers, peptones.

  2. Classify bacteria based on oxygen requirement and define each of the terms

  • Obligate aerobes: Require oxygen.

  • Obligate anaerobes: Cannot survive in oxygen.

  • Facultative anaerobes: Can grow with or without oxygen.

  • Aerotolerant anaerobes: Do not use oxygen but tolerate it.

  • Microaerophiles: Require low oxygen levels.

  1. What is the function of thioglycollate in the media? In a thioglycollate tube, where is the oxygen concentration higher and what indicates the presence of oxygen?
    Function: Reduces oxygen, creating anaerobic conditions.
    Oxygen concentration: Highest at the top.
    Indicator: Resazurin or methylene blue.

  2. Give examples for obligate aerobe, obligate anaerobe and facultative anaerobe and draw the growth pattern of these bacteria grown on a Petri dish in an aerobic condition and in an anaerobic jar.

  • Obligate aerobe: Pseudomonas aeruginosa

  • Obligate anaerobe: Clostridium sporogenes

  • Facultative anaerobe: E. coli

  1. What gases are produced by gas pak? What catalyst is required for the formation of water?

  • Gases produced: Hydrogen (H₂) and carbon dioxide (CO₂).

  • Catalyst: Palladium.

  1. What indicator is used in an anaerobic jar to detect the presence or absence of oxygen and what color changes will you observe with respect to the indicator?

  • Indicator: Methylene blue or resazurin.

  • Presence of oxygen: Blue or pink.

  • Absence of oxygen: Colorless.

  1. What are the toxic forms of oxygen? What are the enzymes required for removing the toxic forms of oxygen?

  • Toxic oxygen forms: Superoxide (O₂⁻), Peroxide (O₂²⁻), Hydroxyl radical (OH⁻).

  • Enzymes: Superoxide dismutase, catalase, peroxidase.

  1. Why do some bacteria grow in the presence of oxygen and others cannot?
    Reason: Some bacteria produce enzymes to neutralize toxic oxygen forms.

  2. Reason the growth pattern of obligate aerobe, obligate anaerobe and facultative anaerobe in the presence, absence and presence/absence of oxygen respectively.

  • Obligate aerobe: Grows only in oxygen.

  • Obligate anaerobe: Grows only without oxygen.

  • Facultative anaerobe: Grows in both conditions