Please remember that 11th and 12th standard are the days when a student really gets motivated to work on his/her project based on their own interests.. So, please follow what topics you really liked in your Biology / Physics chapters and find a project from those chapters..
We can't really suggest you some random projects.. as it will never be useful to do projects what others find them as important..
If you still require our help in this regard.. do tell us some names of chapters in your text book that you really liked.
We can help you with the website locaitons where you can find important research happening.. so that you can get your mind ignited..
our best wishes..
You can find projects of Organ transplant & Stem cells in these places:
basics of what is an organ transplant is here: http://en.wikipedia.org/wiki/Organ_transplant