Secondary-age students were asked about some science-related careers, using an 'interviews-about-scenarios' technique. This article reflects on students' comments relating to the nature of scientific knowledge. Some comments reflected the aim of science as a means to better understand the world and our place in it. Other comments reflected perceptions of the possibility of applying scientific knowledge to engineer change -- something that had great benefits, but also risks. There was also evidence that some students might hold misleadingly positivistic notions about scientific knowledge that may distort perceptions of some areas of scientific work.