On the face of it, the differences between undergraduate and graduate level writing and research should be rather obvious. After all, we expect more of our graduate students than we do of our undergraduate students. Education is a progression, something we build upon and improve upon as we travel through the years. However, just because this makes intuitive sense does not mean that the actual differences between the written products of each level of study are that clear. After all, we expect the grammar, punctuation, mechanics, and other such issues to be correct in both cases. So let's examine some of the differences that should be in play when comparing the two.
First, graduate level students are expected to think on a higher level than undergraduate students. This means the vocabulary should be more sophisticated; the thoughts should be better developed and deeper; the analysis should be stronger; and so forth. The topics don't necessarily have to be very different for each level, but the approach to, and handling of, those topics should differ. For example, an undergraduate and graduate student could each write a paper about global climate change. But while the undergraduate level paper might talk about Gore's "An Inconvenient Truth," and discuss how that movie made some excellent points, the graduate level paper might reference a UN white paper on the matter, and analyze what effect that paper has had upon international policy.
Second, graduate level students are expected to have read and written about a much wider array of subjects, and learned about a much larger variety of theorists, scientists, and other scholars in their particular field(s) of study, than are undergraduate level students. As a result, graduate level papers should include a much deeper referencing of, and building upon, those previous thinkers. It should be clear, not in a name-dropping way, but in a way that shows a true integration of a wealth of knowledge, that the graduate level student has integrated previous work and is building upon it.
Finally, graduate level writing and research (but especially writing) should show a much greater percentage of original thought than does undergraduate level writing. In the early college years, students are absorbing a great deal of knowledge about their chosen area(s) of study. It is not to be expected – and in fact, it is often frowned upon – that students at that level are thinking original thoughts about their disciplines. For example, it would not make sense that an undergraduate would believe he had the answer to a philosophical dilemma that had plagued philosophers for centuries – his depth and breadth of knowledge in philosophy would simply not be there. However, by the time people are graduate students – especially doctoral students – it is expected that they have absorbed that knowledge and are starting to think their own thoughts that extend that knowledge base. Of course, graduate level students continue to research what others have discovered before them, but again, they are expected to contribute to their field(s), while undergraduate level students are not.
Certainly, there are other differences between these two types of writing. However, the basic idea is that much more is expected of graduate level students in the way of sophisticated writing and original thought than is expected of undergraduate level students. While not all graduate students are free-thinking geniuses, and while not all undergraduate students are mere sponges, these general guidelines apply.