I may have a few pointers...

First and foremost, don't think of it as a presentation; think of it as a conversation. It is, essentially. Have fun with it.

Beyond deep breathing, which other posters have mentioned... Stand/sit up straight. Good posture looks good and is likely to benefit your grade... But, more importantly, it will help you feel more confident and relaxed. When you hunch over, you compress your organs, and your lungs are more constricted, which will cause you to feel stressed. Good posture actually has a lot of physical benefits, but I won't get into that...

Maintain eye contact. I noticed that another poster mentioned to look just above someone. Only do this if you absolutely cannot look someone in the eyes. If you can't, I highly encourage you to practice this skill in the future. If you have friends or acquaintances with whom you're more comfortable, look at them more often.

Take your time and articulate what you're trying to say. Don't be afraid of long pauses or silence. A well placed pause is very effective, and it gives you some time to think about what you're going to say next.

I don't know if the topics pertain to something you've been studying recently. If they do, then simply look over what you've been studying so you have some idea of what the topics may be and how you would answer. If they don't, then just wing it... Don't try to imagine each and every question that may be asked and formulate responses. It's highly unlikely you'll even get one of those questions, and you'll only succeed in making yourself more anxious. The only practice I would recommend is getting a few of your friends and having them act as an audience while you talk about any given topic, preferably one they pick for you.

Organize your thoughts. You only have a minute; don't try to write an essay. After you get your topic, scribble a few key words for subtopics that you could go over on a note card. For best results, try to use subtopics that are similar. It'll make the discussion much more comfortable for you if you can easily translate from one subtopic to the next. The key words will help jog your memory if you get stuck, but don't rely on them. Notes are an unnecessary crutch, and the vast majority of speakers do much better without them. You know more about a topic than you think you do.