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Exam 1

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Termini in questo insieme (24)

  • What are the two main sources of carbon for microbes?
    Autotrophs use CO2 as a carbon source, while heterotrophs use organic compounds from other organisms.
  • How do microbes acquire energy?
    Microbes are chemotrophs if they use chemicals and phototrophs if they use light as their energy source.
  • What are organotrophs and lithotrophs?
    Organotrophs use organic molecules as electron sources, while lithotrophs use inorganic molecules.
  • What is the difference between obligate aerobes and obligate anaerobes?
    Obligate aerobes require oxygen for growth, while obligate anaerobes are killed by oxygen.
  • Name four toxic forms of oxygen that can damage cells.
    Singlet oxygen (1O2), superoxide radicals (O2−), peroxide anion (O22-), and hydroxyl radical (OH·).
  • Which enzymes detoxify reactive oxygen species (ROS)?
    Superoxide dismutase, catalase, and peroxidase detoxify ROS by converting them to less harmful molecules.
  • What are facultative aerobes?
    Organisms that can grow with or without oxygen but generally prefer oxygen for aerobic respiration.
  • What is nitrogen fixation and why is it important?
    Conversion of atmospheric N2 to ammonia (NH3) by certain bacteria; essential for making nitrogen available for biosynthesis.
  • Why are trace elements important for microbial growth?
    Trace elements act as enzyme cofactors and are required in small amounts for anabolic pathways.
  • How does temperature affect microbial growth?
    Temperature influences protein and membrane structure; microbes have an optimum growth temperature range.
  • Define psychrophiles, mesophiles, and thermophiles.
    Psychrophiles grow best below 15°C, mesophiles between 20-40°C, and thermophiles above 45°C.
  • How does pH affect microbial growth?
    pH affects protein and nucleic acid folding; microbes are classified as neutrophiles, acidophiles, or alkalinophiles based on pH preference.
  • What is osmotic pressure and how does it affect microbes?
    Pressure from solutes on a semipermeable membrane; hypotonic causes swelling, hypertonic causes shrinking of cells.
  • What are halophiles?
    Salt-loving microbes that require moderate to high salt concentrations for growth.
  • What is quorum sensing?
    Bacterial communication system where cells detect population density via signaling molecules to regulate gene expression.
  • Describe binary fission.
    A form of asexual reproduction where one cell divides into two genetically identical daughter cells.
  • How is generation time calculated?
    Generation time (G) = time interval (t) divided by number of generations (n), \(G=\frac{t}{n}\).
  • How do you calculate the total number of cells after n generations?
    Total cells = initial cells (b) × 2^n, \(B=b \times 2^n\).
  • What are the phases of microbial growth in batch culture?
    Lag phase, log (exponential) phase, stationary phase, and death (decline) phase.
  • What is a chemostat?
    A continuous culture system that maintains microbial populations in a specific growth phase by adding fresh medium and removing old.
  • Name two direct methods to count microbial cells without incubation.
    Electronic counters like Coulter counters and flow cytometry.
  • What is the viable plate count method?
    A direct counting method using serial dilutions and plating to count colony-forming units (CFUs) after incubation.
  • What is the most probable number (MPN) method?
    A statistical method estimating bacterial concentration based on dilution series and growth in multiple tubes.
  • How does turbidity estimate microbial population size?
    Indirect method measuring culture cloudiness with a spectrophotometer; more turbidity indicates higher cell density.