1. introduction

Background Research

There are three different types of UV rays, and there's a common misconception that they all do the same thing. While they are similar, each type of ray has a different wavelength and can penetrate surfaces to a certain extent.


UV-A has the longest wavelength of 320-400 nm and is responsible for 95% of the UV radiation that reaches the Earth's surface. These rays penetrate deep into the skin and are a factor in premature aging.


UV-B is likely the UV ray you are most familiar with, as it is what will give you sunburns and possibly skin cancer (shameless plug for sunscreen!)! This ray has a wavelength of 280-320 nm.


UV causes the formation of lethal thymine dimers on bacterial DNA. It has been demonstrated that UV is effective in killing microorganisms contaminating the surfaces of a variety of materials. Thus the number of bacteria would reduce as the duration of the bacteria under the UV light increases. Ultraviolet (UV) light is a type of light, invisible to the human eye, that exists on the electromagnetic spectrum between X-beams and visible light and which travels in a vacuum with the same speed of light equal to c. We are presented with low levels of UV light from the sun’s beams each day, although the ozone layer consumes a significant part of the UV energy. The UV light has three different bands depending on the wavelength; the UV-A, UV-B and UV-C light spectrums. This spectrum differs in their wavelengths.



UV or ultraviolet light is a type of radiation. In simple terms, when bacteria or another type of microbe is directly exposed to certain types of UV light, the DNA (its fundamental building block) of the cell is damaged, preventing it from replicating. If a cell cannot reproduce, then the cell cannot cause infection, which is how UV light kills bacteria.


The UV process is a physical process as opposed to the addition of chlorine to the water to address microbiological issues which is a chemical process. This is important, because it allows UV to kill bacteria and other microorganisms without adding anything to the water or creating what is known as disinfection by-products (like trihalomethanes, called THMs for short, which are proven to be carcinogenic).

Research Questions

How UV exposure affects the growth of bacteria in the water?

How Multiple screening for the bacteria with UV Rays affects the number of bacteria compared to once?

    Hypothesis

As the amount of time the pond water is exposed to UV rays increases, the lesser the amount of bacteria that would survive. The independent variable is the amount of time the bacteria in the pond water is exposed to the UV rays. The dependent variable is the number of bacteria left after UV exposure. The controlled variable is the amount of pond water to be placed in the agar plates (dripped onto the agar plates as it can affect the number of bacteria in the results later on.)