This question allows you to get a little bit of your personality across to the interviewer as well as describing your relationship with science. The subject of your answer is unimportant but it would benefit you to talk passionately. Good responses may be that you enjoy problem solving or discovering new information. To add depth to your answer you could describe how you have always had a relationship with science or describe your inspiration. Think carefully and research an answer that is appropriate to the role for which you are applying.