Some aspects of Visual Basic for Applications (VBA) which runs alongside Excel are not available on the Mac. What is most likely happening here is that your professor has used ActiveX controls (buttons etc) which will not work on the Mac. They just appear as bitmap images. He/she could have used buttons from the Forms toolbar which would have worked on both platforms.
The only way to remedy this is to re-write some of the spreadsheet code. If it's just a few simple things, it might be quite easy to do, but it depends if you are familiar with VBA or not.