Undergraduate / "finding employment in the medical field" - UC Prompt #1 [4]

"Every day I am subjected to stories of how my parents have shaped another person's life, while I listened."
I'm thinking you should take out "while I listened" because wouldn't that make it a bit redundant?

Undergraduate / Foundations of Journalism / Middle ages - NYU academic areas of study [8]

maybe cut out what you originally wanted to be and how long you've been volunteering...
Or perhaps join that with something else.
You have a good idea with giving being your passion and NYU being the place that will help with that, so maybe focus a little more on those two.

Undergraduate / "a second generation child in America" - my family and my world [4]

Personally I think this is well done.. Unfortunately, I don't think it answers the prompt... it asks for your dreams and aspirations and although you caught my attention, I don't think it says anything about your dreams.

Undergraduate / "The Key to all Doors" - UC Prompt #1 [3]

Ever since I started the application process for universities I have realized how fortunate I am for having the opportunity to an education. I am a first generation student going to college, which I'm proud of.(that seems a little out of place, try rewriting it to tie into the privileges the US gives you) I believe that it is a privilege to be in the United States of America, which offers an infinite number of opportunities to better the lives of those who want to better themselves, like myself. I come from a very modest family who migrated from Mexico for the only purpose that their children, my sister and I could study,(it seems a little unnecessary to state you and your sister) because in Mexico it would not be possible. From then on,(from when? I don't think you stated a time) I have struggled a lot to learn the language, that has not been easy but I have never given up, and also to do my assignments since both of my parents were not able to help me. However, I have overcome my struggle with the help of others and my very own efforts. All the challenges I have gone through have shaped my dreams and aspirations because I know that every effort has made me stronger, (something needs to be added here to make the sentence more fluid ) will pay back the day that(take "that" out) I obtain a career .

My parents taught me to dream big, to do my best and I will achieve.(my parents taught me that if I dream big and do my best I will achieve.) Every time I remember their words, I get sentimental and give myself an extra push to follow the path for success, which is education. With this in mind I plan to achieve and overcome any circumstances that life can put me into prove(take out "prove" or perhaps separate "into" to "in to") . Everything that comes I will use it(take out "it") as a stepping stone to help me get anywhere I want. I believe that maintaining positive is the key to walk thought the road of success. I know that to any university I go to I will be a great student, that will accomplish a lot for the school and for myself.