I would agree with Variola's answers ; just seen that she has replied in between me typing and pressing post. 
 
  Stick to third person and also try to keep tenses simple; verbs referring to an object should be self-consistent.  I would avoid rhetorical questions, they are a verbal flourish rather than a written device; don't you agree? Don't make lists with missing entries :-) A benefit must be shown against a historical background, my understanding is that you are describing the technological advance and explaining the benefits this advance has wrought; this needs a little bit of before and after.  maybe a critical eye would be useful as well; have health gains been universal? what threats are on the horizon (super-bugs?)? is it technology that is providing gains or ways of living (ie drugs/machines vs diet/cleanliness)? 

  Although essays need plans - I firmly believe that it is essential to get your prose down on paper and then go about chopping it about and re-editing.  read and re-read before handing in any work.  if it is an important essay - get someone else to read it through.  this is not in order to cheat or to plagiarise.  You can be so familiar with your own arguments that you fail to see the gaping hole; others, even if not a specialist will spot it straight away.

Good Luck!
Matthew

And do use the spellcheck!  Good format, spelling, grammar, and presentation all make an essay easier to read and easier to give a good mark to.