2.7 bio-Micro organisms

• Growing micro-organisms


  1. Micro-organisms can be cultured to increase their population numbers, enabling scientists to study them more easily

  2. Each bacterial colony arises from a single cell, enabling the estimation of the number of cells in the initial culture

  3. Clumping of cells can lead to misleading estimates

  4. Culturing may be done using solid agar or a nutrient broth

  5. The culture medium contains the essential nutrients required by the micro-organisms
• Aseptic techniques


  1. Aseptic techniques reduce contamination from other micro-organisms

  2. To avoid contamination of samples: Sterilise all equipment and surfaces before and after the experiment

  3. Inoculating loop held in the Bunsen burner flame to kill any bacteria already present

  4. Flame the rim of the culture bottle (before and after a sample of culture is removed) to create an updraft of air moving out of the bottle (prevents contamination of the culture)

  5. Lid of agar plate lifted only slightly, keeping it low over the agar

  6. Inoculating loop sterilised again (after transfer of the culture) in the Bunsen burner flame
• Effect of temperature on the growth of bacteria

  • Bacteria grow most rapidly at warm temperatures (optimum)
  • If the temperature rises too high above this optimum, the bacteria are killed
  • If temperatures fall too low, the rate of growth decreases
• Food preservation


  • Food is refrigerated to slow the growth of micro-organisms, allowing it to last longer before becoming spoilt
  • Freezing completely stops growth
• Penicillin is an antibiotic
• At warm temperatures (optimum)


  Bacteria grow at their best
• If the temperature rises too high above the optimum

  The bacteria are killed
• If temperatures fall too low

  The rate of growth decreases
• Food preservation


  1. Refrigeration slows the growth of micro-organisms, allowing food to last longer before spoiling

  2. Freezing completely stops growth
• Production of penicillin


  Penicillin is an antibiotic produced by the Penicillium fungus and can be prepared industrially using a fermenter
• Conditions controlled in a fermenter

  • Temperature
  • Oxygen levels
  • pH
  • Nutrient levels
• Optimum temperature for Penicillium is between 23 to 28°C
• Penicillium respires aerobically so it requires oxygen
• Optimum pH for Penicillium is around 6.5
• Penicillin is produced at low nutrient levels only
• How to control conditions in a fermenter

  1. Aerobic respiration in Penicillium produces heat, cooling jacket cools the culture

  2. Sterile air enters via the air intake

  3. pH probe used to monitor pH levels

  4. Acid/alkali intake enables adjustment of pH levels

  5. Once growth has started, no further nutrients are added

  6. Liquid medium is drained and filtered after approximately 200 hours

  7. Chemicals are added to extract the penicillin