Purchasing Manager Question:

Again, companies want to hire people who are passionate about the job, so you should have a great answer about why you want the position. (And if you don't? You probably should apply elsewhere.)
First, identify a couple of key factors that make the role a great fit for you (e.g., "I love customer support because I love the constant human interaction and the satisfaction that comes from helping someone solve a problem"), then share why you love the company (e.g., "I've always been passionate about education, and I think you guys are doing great things, so I want to be a part of it").