1. Introduction


Bacteria are often maligned as the causes of human and animal disease. Studies and research have shown that most bacteria might be harmful but there are also good bacteria that benefits mankind in many ways. People might wonder how they can stay away from all these bad bacteria and keep the good ones. Such methods are so sophisticated, and only used in experimental labs. Bacteria seems so easy to understand- some harmful, good and tiny. But is more complex then any normal person thinks. So many types of beneficial or harmful bacteria, and new ones are getting researched every minute. People have the knowledge but do they understand the philosophy behind all these tiny living things? Does people know that UV disinfection is the best way of getting rid of bacteria? Our investigation seeks to find out how UV light affects the growth of these bacteria. Studies have shown that bacteria will get mutated if it has been exposed to UV for a period of time. Mutations are a heritable change in the base sequence of DNA. We learned previously that some mutations can be neutral or beneficial to an organism, but most are actually harmful because the mutation will often result in the loss of an important cellular function. Mutations occur naturally in bacteria at a rate 10-7 – 10-8 per base pair during one round of replication. In the presence of a mutagen,however this rate can increase dramatically. Mutagens can be in the form of a chemical, such as nicotine, or in the form of electromagnetic radiation. There are two forms of electromagnetic radiation that are mutagenic; ionizing radiation and non-ionizing radiation. Ionizing radiation, such as x-rays or gamma radiation carries enough energy to remove electrons from molecules in a cell. When electrons are removed from molecules, ions called free radicals are formed. Free radicals can damage most other molecules in a cell, such as DNA or RNA, by oxidizing them. Non-ionizing radiation, such as ultraviolet (UV) light, exerts its mutagenic effect by exciting electrons in molecules. We decided to test if this was true on E coli and B subtilis. E coli can be found in our intestines and it is a harmful bacteria as it causes diarrhea. In contrast, Bacillus subtilis occurs independently in the environment around us and was first used by Nazi army to manage diarrheal illness. It helps in normalizing gut motility and metabolic functioning. We exposed them to UV and let them grew.

Our hypothesis is 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.

The independent variable: Growth rate of bacteria
The dependent variable:   Time bacteria is exposed to UV ray
The constants variables:  
Intensity of UV ray                                       
The amount of bacteria exposed to UV ray
Size of petri dish
Time each bacteria is allowed to grow
Humidity of environment around bacteria
Distance between the bacteria and the UV light source

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