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Measuring Growth by Biomass quiz

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  • What does a spectrophotometer measure to estimate microbial biomass in a liquid culture?
    A spectrophotometer measures light absorbance values, which indicate the turbidity or cloudiness of the culture due to microbial growth.
  • How does turbidity relate to microbial biomass in a liquid culture?
    Higher turbidity means higher microbial biomass because more organisms make the culture cloudier.
  • What does a high absorbance value from a spectrophotometer indicate about a culture's biomass?
    A high absorbance value indicates a high biomass, meaning there is significant microbial growth in the culture.
  • Why does high turbidity result in lower detected light in a spectrophotometer?
    High turbidity scatters and absorbs more light, so less light passes through to the detector.
  • What is the relationship between absorbance value and detected light in a spectrophotometer?
    As absorbance value increases, the amount of detected light decreases because more light is absorbed or scattered by the sample.
  • What is the minimum requirement for using a spectrophotometer to measure microbial biomass?
    The liquid culture must have a relatively high concentration of cells to be cloudy enough for the spectrophotometer to detect biomass.
  • What is the range of absorbance values typically measured by a spectrophotometer in these experiments?
    Absorbance values typically range between 0 and 1.
  • What is another method, besides spectrophotometry, to measure microbial growth by biomass?
    Another method is measuring the total weight of microbial cells by centrifuging the culture to form a cell pellet and then weighing it.
  • What does a centrifuge do in the process of measuring microbial biomass by weight?
    A centrifuge spins the sample rapidly to create centrifugal forces that pull cells to the bottom of the tube, forming a cell pellet.
  • What is the supernatant in the context of centrifugation?
    The supernatant is the liquid that remains above the cell pellet after centrifugation and is carefully removed before weighing the pellet.
  • Why must the empty tube be weighed before measuring the cell pellet's mass?
    Weighing the empty tube allows you to subtract its mass from the total, so you get the mass of just the cell pellet.
  • How does the mass of the cell pellet relate to microbial growth?
    A greater cell pellet mass indicates more microbial growth in the original culture.
  • What happens to cells in a liquid culture during centrifugation?
    Cells are pulled to the bottom of the tube by centrifugal force, forming a concentrated cell pellet.
  • What is the main limitation of using a spectrophotometer to measure microbial biomass?
    The main limitation is that the culture must be sufficiently cloudy, meaning it needs a high enough cell concentration for accurate measurement.
  • What are the three possible fates of light as it passes through a liquid culture in a spectrophotometer?
    Light can be absorbed, transmitted (pass straight through), or scattered by the culture.