I agree with Sean, especially about the metaphor. Also, imho, the sentence:
ambition of becoming a Doctor was expected of me
seems like it was forced and not your choice. I know it is your choice, and you explain it in the rest of the essay, but I just dont think that that sentence is necessary.
Therefore, I will attend a university with a strong biological research department to further my knowledge of biology and be helpful to the mankind.
^That last sentence is good, but the part about being "helpful to mankind" does not fit with the rest of the sentence. It just seems like you just put it there to sound good.
But, I think it's good besides that.