4. Discussion

4.1 Key finding

From the data we collected, We could deduce that for both E.coli and B.subtilis, the amount of bacteria colonies decreases when the time of exposure to UV light increases

4.2 Explaination of key findings

Studies show that when DNA is irradiated with UV light, some of that light is absorbed by the ethylene bond in pyrmidine (thymine, T, and cytosine, C) bases in the DNA. This energy permits the formation of new bonds between adjacent pyrimidine bases, forming dimers (pairs connected by covalent bonds) of pyrimidines. Most of the time, this happens with thymines, forming thymine dimers, but cytosine dimers and thymine-cytosine heterodimers can also be formed. For the DNA of E.coli and B.subtilis, it would have the same effect on them hence hindering the rate of growth of the colonies.

4.3 Evaluation of hypothesis

Our hypothesis 'The longer the bacteria is exposed to the UV light source, the slower the bacteria will grow and sometimes even killed if exposed for too long.'
Our hypothesis was proven to be true with with our bacteria exposed to 1 hour of UV ray unable to grow and a decrease in colony when the time of UV exposure increases. However the effect is stronger for B.subtilis and E.coli is more resistant

4.4 Areas of improvement

Our experiment could have been more accurate if we made sure our petri dishes containing bacteria was dry so some of our plates would not have been accurate as it has water droplets on the agar causing the bacteria to not be able to grow well.

Another area of improvement is that we could have used serial dilution to reduce the concentration of microscopic organisms or cells in a sample. As for instance the number and size of bacterial colonies that grow on an agar plate in a given time is concentration dependent

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