You should give a picture of how you see your future. Do you see your graduate study as preparation for a career in industry, government, or academia? You should also give a picture of how your past shaped you and your record. For example, you can describe what motivated you to seek a graduate degree in Biophysics. Was this something you wanted to do since before you went to college or was it something you realized after you had graduated from college and worked in industry for a while? Were you inspired by a book, a teacher, a colleague, or a parent? You can also use this statement to address any unusual circumstances that will show up elsewhere in your record. For example, if illness caused you to take leave from school for a semester, say so. If you transfered between many schools, say why.
The above paragraph is only intended to give you some guidance in preparing your statements. Do not be constrained by it. Address only points that you feel are important, whether they are suggested above or not. If you feel the only way to address your objectives is by explaining your past then you can combine the two statements into one.