Well where to start? You may hear most, some, or little of what I describe. Many will ask you about your reason for choosing to undergo the rigourous path in graduate studies, what has prepared you for this challenge, as well as hobbies or interests you have had. You may also be asked why did you choose the institution, what previous research experience do you have, and may inquire further about your scientific coursework in college (they may likely probe any areas of weakness in your academic record as well). You may likely be asked about your presentation skills, since you willl do PLENTY of that in a graduate program. There are so many possible questions that it is hard to cover them all, but that should give a very rough flavor of the types of questions you may be asked.