2. Materials and Methods

Independent Variables:
1. Material of water bottles
Dependent Variables:
1. Amount of bacteria water
Constant Variables:
1. Volume of water in water bottles
2. Volume of water consumed
3. Who drinks the water
4. Intervals between water consumption
5. Temperature of the room
6. Osmotic pressure of the room
7. pH of medium
8. Intensity of Light


    1. Fill all bottles with cold water to the brim, taking note of the time.
    2. Fill up a beaker to act as a control.
    3. Every two hours, drink similar amounts of water from each bottle. (Only one person should be drinking as individuals have varying bacteria in their mouth)
    4. After twelve hours, start up a flame at the methylated spirit lamp to heat the mouth of the centrifuge tubes.
    5. Serial dilute 1µl from the bottles’ water into 999µl of sterile water.
    6. Use a micropipette to take 100µl of water onto the agar plates and spread onto Lysogeny Broth (LB) agar plates. (Remember to label the plates)
    7. Incubate the plates at 37°C for 1 day.
    8. After incubation, interpret and record the number of colonies in each plate.
    9. Once recording is done, dispose of the plates. (Biohazards)
    10. Repeat steps 3 to 9, refilling all bottles with the similar amounts of water - at the same time - if they run out of water.
    11. After 3 days of testing, stop the experiment. 

    Risk assessment and management

    1. As this experiment involves heating, use mittens or tongs when carrying hot liquids or objects to prevent being burned.
    2. As the experiment involves chemicals, avoid consuming these chemicals or being in contact with it to prevent any injuries.
    3. As the experiment involves bacteria, avoid inhaling in the bacteria and always wear gloves to prevent bacterial infections.
    4. As the experiment involves bacteria, ensure that the petri dishes are always closed so that bacteria is not inhaled, preventing bacterial infections.

    Method of analysis of results

      1. Tabulate the data of the colonies of bacteria.
      2. Taking overgrown colonies as 50 units each, plot a graph of the average colonies of bacteria against the time taken.
      3. From the graph, we can find out the bottle with the fastest bacteria growth.
      4. From the graph, we can know which bottle has the most bacteria present.

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