Final answer:
A UV light is used for presumptive tests in biological applications like DNA visualization after gel electrophoresis, detecting microbial presence, and methods of disinfection. It is instrumental in genotyping and the use of UV spectroscopy with Nanodrop spectrometers or disinfecting with UV lamps.
Step-by-step explanation:
A UV light is used when performing presumptive tests with DNA and bacteria, among other biological applications. For instance, DNA fragments can be visualized under UV light after being separated by gel electrophoresis and stained with a fluorescent dye. This is crucial in genotyping, which helps in identifying and mapping various DNA sequences. Similarly, in a microbiology context, UV light is utilized in methods like the Wood's lamp to detect fungal infections or to check the sterility of a workspace or tools since microbial DNA absorbs UV light forming thymine dimers which can be lethal.
Moreover, the use of a Nanodrop spectrometer for UV spectroscopy allows the measurement of DNA concentration in small volumes. This instrument relies on the absorbance of UV light by nucleic acids to quantify them. Lastly, UV lamps emitting light at a wavelength of 260 nm are regularly used in disinfection procedures to control microbial growth, as UV light has the ability to induce mutations and kill microorganisms.