Independent Variable: Type of plant used
Dependant Variable: The diameter in cm of clearing
Confounding Variables: Room temperature
Concentration of plant solution
Volume of plant solution
No food or drink was to be consumed during the experiment as we were using living bacteria which could harm our health.
When using the methylated spirits eye goggles were worn to prevent it from splashing into our eyes.
Lab coats were worn throughout the experiment to protect our clothes from methylated spirits.
To avoid contamination during this experiment I used the following aseptic techniques:
Washed hands thoroughly before and after experiment.
Disinfected work surfaces with 1% Virkon
No eating or drinking
Made sure equipment was sterile before use by immersing in methylated spirits and then heating in a Bunsen burner.
Reliability of Results
To make sure my results were reliable I repeated it many times and found the average. Extreme anomalies have been left out of the data used. I also recorded the results of a control for both variables. The control was soaked in methylated spirits to see if this inhibited the growth of bacteria also.
After analysing the data obtained from the experiments I worked out the average diameter or bacteria cleared by each disk. I can see from my results that the garlic was more successful at clearing the bacteria. The average clearing by garlic was 9.56 mm. However the mint solution made an average clearing of 7.43 mm. This is a lower value than the garlic and so I can deduce that garlic has better antibacterial properties than mint. The results vary quite a lot which suggest unreliability. In this experiment we used dried mint leaves, if we had used fresh leaves the results may have been more reliable.
If I had the chance to repeat this experiment I could obtain better results by doing the following things:
Leave the paper to dry fully before placing it in the agar
To increase the accuracy when measuring the solution I could have used a syringe instead of a pipette.
Use fresh mint leaves instead of dried mint leaves to increase the validity of my results.
Use equipment like a blender to crush the mint leaves and cloves of garlic for the same amount of time each time, for example 10 seconds.
Carry out experiment in completely aseptic conditions instead of on a disinfected classroom table.