Factors Affecting Bacterial Growth (Leaving Cert Biology): Revision Notes

Factors Affecting Bacterial Growth

Factors that affect bacterial growth include:

1. Temperature
2. Oxygen concentration
3. pH
4. External solute concentration
5. Pressure

1. Temperature

• Bacterial growth is controlled by enzymes so most bacteria grow best between 25°C and 45°C.
• Some bacteria can grow in extreme temperatures, such as 0°C or 80°C.

2. Oxygen Concentration

• Oxygen availability determines how bacteria respire.
• Aerobic bacteria: need oxygen to survive (oxygen is needed for respiration).
• Anaerobic bacteria: do not need oxygen for respiration.
  • Obligate anaerobic bacteria: can only respire in the absence of oxygen.
  • Facultative anaerobic bacteria: can respire with or without oxygen.
  • Aerotolerant anaerobic bacteria: do not require oxygen but can survive in its presence.

3. pH

• pH affects enzymes, which are essential for bacterial survival and reproduction.
• Most bacteria require a neutral pH.

4. External Solute Concentration

• High solute concentration:
  • In a salty or highly concentrated environment, water leaves the cell by osmosis, causing the bacteria cell to shrivel and die.
  • Example: This principle is used in food preservation, like salting fish.
• Low solute concentration:
  • In a low-solute environment, water moves into the cell by osmosis, causing it to swell.
  • The cell wall prevents the bacteria cell from bursting.

5. Pressure

• High pressure can inhibit bacterial growth by causing the cell walls to collapse.
• Some bacteria, like those found on the ocean floor, have adapted to survive in high-pressure environments.