Microbiology 4

• What is one of the learning outcomes related to cell growth?

  Cell growth
• What process do bacteria use to replicate?

  Binary fission

  
• How is growth defined for multicellular organisms?

  Growth involves the whole organism getting bigger
• How is growth defined for single-celled organisms?

  Growth is an increased number of cells
• What is the term for the time required for binary fission to occur?

  Generation time
• What factors influence generation time in bacteria?

  Nutritional and environmental factors
• What is the generation time of E. coli in a laboratory culture?

  About 20 minutes
• How does bacterial growth in nature compare to laboratory conditions?

  Cells grow much slower in nature
• What is measured in a laboratory experiment regarding bacterial growth?

  The dynamics of population growth
• What happens to the population every 30 minutes in a bacterial growth experiment?

  The population doubles

  
• What are the two scales that can be used on the y-axis of an exponential growth graph?

  Arithmetic scale and logarithmic scale

  
• What is a semi-logarithmic graph?

  Logarithmic scale on y-axis, linear on x-axis
• How do you plot data on semi-logarithmic graph paper?

  Plot absolute values without conversion
• What does each block of ten lines represent on semi-logarithmic graph paper?

  Increase by power of ten
• How can generation time be estimated using semi-logarithmic graphs?

  By calculating the number of generations
• What is the formula for calculating the final cell number in exponential growth?

  N = N0$2^n$
• How can you calculate the number of generations during exponential growth?

  n = logN - logN0 / log2
• What does the variable 'n' represent in the growth calculation?

  Number of generations during growth
• If the initial cell number is $2.5 \times 10^7$ and the final cell number is $10^8$, how many generations occurred?


  2 generations
• What is the generation time if there are 2 generations in 2 hours?

  1 hour
• What are the phases of bacterial population growth in closed systems?

  • Lag Phase
  • Exponential Phase
  • Stationary Phase
  • Death Phase

  
• What occurs during the lag phase of bacterial growth?

  Time before significant growth occurs

  
• What factors affect the length of the lag phase?

  History of inoculum and growth conditions
• What happens during the exponential phase of bacterial growth?

  Cell population doubles at regular intervals

  
• Why can't organisms grow exponentially indefinitely in closed vessels?

  Nutrients run out and waste builds up
• What occurs during the stationary phase of bacterial growth?

  No net increase or decrease in cell numbers
• What characterizes the death phase of bacterial growth?

  Exponential decline of viable cells

  
• What are the methods to measure bacterial growth?

  1. Microscopic counts
  2. Viable counts
  3. Spectrophotometry

  
• What is the purpose of microscopic counts in measuring growth?

  Count the number of cells present
• What is a counting chamber used for?

  To count cells under a microscope
• What is a viable count?

  Count of cells able to divide
• What is the spread plate method?

  Sample spread evenly over agar surface

  
• What is the main assumption of viable counts?

  Each viable cell forms one colony
• What does spectrophotometry measure in bacterial growth?

  Light scattering to estimate cell mass
• What is a limitation of spectrophotometry?

  Turbidity does not equal cell number
• What are the issues with microscopic counting?

  • Dead and live cells indistinguishable
  • Imprecise counting
  • Small cells difficult to see
  • Debris may be mistaken for cells
• What are the sources of error in viable counts?

  • Culture medium and incubation conditions
  • Mixed cultures affect growth rates
  • Colony sizes vary
  • Inaccurate pipetting and non-uniform samples
• What are the issues with spectrophotometry?

  • Turbidity ≠ number of cells
  • Cell size matters
  • Debris causes false positives
  • Clumping affects readings
• What is the summary of bacterial growth?

  • Bacterial cells grow by binary fission
  • Growth phases: lag, exponential, stationary, death
  • Growth can be measured in various ways