CHAPTER 4

• How is microbial growth defined?


  As the increase in the number of cells, which occurs by cell division.
• What is the primary method of cell division in bacteria?


  Binary fission.
• Describe the budding process in microbial growth.


  A new cell grows out of the parent cell and eventually detaches to become independent.
• In which organisms is budding common?


  Yeast, some fungi, and some animals like hydra.
• What occurs during binary fission?


  The parent cell divides into two equal halves, each becoming a daughter cell.
• What is the standard bacterial growth curve composed of?


  Lag phase, log phase, stationary phase, and decline phase.

  
• What happens during the lag phase of bacterial growth?


  Organisms do not increase significantly in number but are metabolically active.
• Why is the lag phase important for bacteria?


  It allows bacteria to adjust to the new medium and produce necessary enzymes.
• What characterizes the log phase of bacterial growth?


  Population growth occurs at an exponential rate with rapid cell division.
• What is the generation time in the log phase?


  A regular, genetically determined interval at which the population doubles.
• How can logarithmic growth be maintained?


  By using a chemostat that continuously adds fresh medium.
• What occurs during the stationary phase of bacterial growth?


  New cells are produced at the same rate as old cells die, keeping the population constant.
• What factors contribute to the stationary phase?


  Limited nutrients, toxic waste accumulation, and inadequate oxygen supply.
• What happens during the decline phase of bacterial growth?


  The number of live cells decreases at a logarithmic rate as the medium becomes less supportive.
• What is involution in the context of bacterial decline?


  Cells assume unusual shapes, making them difficult to identify.
• What is serial dilution?


  A technique used to prepare samples with successively lower concentrations of a substance.
• What is the purpose of a pour plate method?


  To mix a sample with agar medium and trap bacteria in the solidified agar.
• How is a spread plate method performed?


  The sample is spread onto the surface of an agar plate using a sterile spreader.
• What does CFU stand for?


  Colony-forming units.
• What is the equation to calculate the number of bacteria in the original sample?

  N = (D)(C), where N is the number of bacteria, D is the dilution factor, and C is the number of colonies counted.
• What does the dilution factor represent?


  The ratio of the volume of solvent to the volume of the original sample.
• What is a Petroff-Hausser counting chamber used for?


  To count cells, such as bacteria and sperm.
• What is the Most Probable Number method?


  A statistical method of measuring bacterial growth when samples contain too few organisms for reliable plate counts.
• How does filtration measure microbial growth?


  By filtering the sample through a membrane filter that traps microbes.
• What does turbidity indicate in a culture?


  A cloudy appearance indicates the presence of microorganisms.
• How is turbidity measured?


  Using a photoelectric device like a colorimeter or spectrophotometer.
• What is the relationship between absorbance and bacterial concentration?


  The amount of light transmitted decreases in proportion to the number of bacteria present.
• What does metabolic activity indicate in terms of bacterial growth?


  It is in direct proportion to the number of bacteria present.
• What does dry weight measure in bacterial growth?


  The moisture removal of a bacterial suspension.
• What are acidophiles?


  Organisms that grow best at a pH of 0.1 to 5.4.
• What pH range do neutrophiles exist in?


  pH 5.4 to 8.5.
• What are alkaliphiles?


  Organisms that exist from pH 7.0 to 11.5.
• What are psychrophiles?


  Cold-loving organisms that grow best at temperatures of 15°C to 20°C.
• What distinguishes obligate psychrophiles from facultative psychrophiles?

  Obligate psychrophiles cannot grow above 20°C, while facultative psychrophiles can grow above that temperature.
• What temperature range do mesophiles prefer?


  Between 25°C and 40°C.
• What are thermoduric organisms?


  Organisms that ordinarily live as mesophiles but can withstand short periods of high temperatures.
• What temperature range do thermophiles prefer?


  From 50°C to 60°C.
• What are obligate thermophiles?


  Organisms that can grow only at temperatures above 37°C.
• What are facultative thermophiles?


  Organisms that can grow both above and below 37°C.
• What is the minimum growth temperature?


  The lowest temperature at which cells can divide.