There are a lot of universities that teach Maths or Biology or whatever. Explain what makes University of Pennsylvania the best? Maybe, it’s that particular teacher you want to learn from? Or the practice lessons, laboratories, and other facilities? Possibly, the interdisciplinary studies will allow you to connect different science areas to achieve your goals? Add some personal touch. What is the most important for you except the learning process? We all are living, breathing people and want to see the community that fulfills our needs. Tell the admission committee more about the extracurricular activities you are interested in. How do you plan to contribute to them, what else do you want to see among them? Share your plans for the future. Once become a part of the alumni family, your reputation will be the university’s reputation. So it’s fair to tell some words about your future way in life. Do you plan to become a scientist, work for a corporation, help people somewhere, or do something else, totally unique?