Three wasnt any written test for me .. as my 10th, 12th and B.Tech aggregates were over 75%.

Nothing much. They asked few basic Questions about C++, other software packages and languages that are taught to us. There were few biotechnology Questions (define biotechnology!) also

personal introduction followed by Why do you want to change the field? and where do you want to see yourself after 5 years?

Learn the basic of all the subjects taught you in your class...
basics of C are necessary which was taught in 1st year.