jaibik, i haven't applied for grad schools yet. but i can give you some tips based on my essay/statement writing experiences for internships and memberships of research organizations. 

- talk about what research you did. like, whose lab you worked in, what project you had, and what you did after the project (results/papers/presentations, if any). you don't have to explain everything (like what assays you ran, or what buffers you used, that'd be too much). just say what you did and briefly state if anything productive came out of it.
- write what inspired you to join biomedical research and why you want to keep on being involved in research
- if you have already made your mind about what kind of project you want to do during gradschool, do a little bit of research on the school's faculties and write name of 1 or 2 profs and include your interest in the type of research they do.

that should be more than enough. remember, grad schools look for 3 main things (said by nation's one of the top school's grad school admissions committee director): how passionate you are about research, what you did during undergrad (mentored research, internships, etc), how wiling you are to fail and learn from you failures.
good luck man!