Chemistry and Biological Chemistry personal statement example

Personal statement example

For two weeks last spring our kitchen table was covered in apple slices. I had cut them into equal wedges, set them on a sheet of white card under the same lamp, and photographed them every ten minutes with my phone clamped to a shelf. Some were dipped in lemon juice, some in salt water, some warmed briefly in a bowl over the kettle, and some left alone as controls. I was trying to find out how quickly polyphenol oxidase turns a cut apple brown, and which treatment slows it most.

The chemistry turned out to be more interesting than the browning. The enzyme uses oxygen to oxidise phenolic compounds in the fruit into quinones, which then react further to form brown pigments. Reading around this, I learned that the enzyme contains copper at its active site, and that ascorbic acid in lemon juice works partly by reducing quinones back before they can polymerise, while the low pH also suppresses the enzyme. I measured browning by opening each photograph in a free image editor and recording the average brightness of a fixed square on each slice. The method was crude, as lighting shifted slightly over the afternoon, so I added a grey card to every frame and corrected each reading against it. With that correction, the lemon-juice slices stayed noticeably paler for far longer than the controls, and briefly heated slices browned more slowly too, which fitted the idea of partly denaturing the enzyme. I wrote it up in six pages and showed my Chemistry teacher, who pointed out that I had confounded acidity with antioxidant effect. I am now planning a second round using a vitamin C tablet dissolved in water, buffered to neutral, to separate the two.

Measuring colour properly became a theme. In class I worked with two friends to build a simple colorimeter from an LED, a light sensor and a microcontroller. One wrote the code and another built the housing from black card. My job was calibration: I made up a dilution series of copper sulfate solutions and checked that absorbance rose in a straight line with concentration, as the Beer-Lambert law predicts. It did, until the most concentrated samples, where the readings levelled off. Working out that our cheap sensor was saturating, rather than the law failing, was one of the most satisfying afternoons of the year. Our device now sits in the prep room and younger students use it.

I am drawn to chemistry where it meets living systems because that is where the questions feel most alive to me. Nick Lane's The Vital Question explained how cells store energy as a proton gradient across a membrane and use it to make ATP. Having balanced redox equations in lessons, I found it striking that the same electron transfers power every cell in my body. It made me want to understand biological reactions at the level of molecules and mechanisms, not only as diagrams.

Outside school I work weekend shifts as a kitchen porter in a busy café. It is not glamorous, but it has taught me to keep a workspace organised under pressure, to follow hygiene procedures exactly, and to stay cheerful during a Sunday rush. I also play trombone in a community brass band, where I sit beside players three times my age and have learned that a section only sounds good when everyone listens as carefully as they play.

I enjoy working out how something happens, designing a way to test it, and then admitting honestly what my measurements can and cannot show. I would like to develop those habits through rigorous study of chemistry and its biological applications, with proper instruments and teachers who will question my methods as usefully as mine has.