There is a vast difference between undergraduate studies and graduate studies. It is like comparing Kindergarten to High School. One prepares you for the other, but they are very different if how and what they are teaching you.
Undergraduate school is what you do when you first leave high school and want to pursue a higher education. It is your first experience at education on your own. Except for that rare individual, you are often unsure about fields of study and in some cases even how to study! Teaching and helping the student determine this is the purpose of an undergraduate degree. This is why the courses and topics are varied and wide ranging in most Universities. There are various writing courses as every field requires you to be able to communicate, this is the same reason most schools will require public speaking. As an undergraduate, you will be given a choice of electives, this allows you to delve into other areas that might be of interest. Many undergraduate students will change majors before finishing their degree.
The graduate program is usually very specific and focused. You have your undergraduate degree and now you really want to become as knowledgeable in a specific area as possible. Graduate studies generally do not have courses outside of the field of study, and in some programs you may be under a private mentor working on specific projects and take very few courses. The undergraduate was learning about school and how to learn, the graduate study can be fun, but it is intense and detailed. The graduate student may take elective courses, but they are rare and not required.
You should now be able to clearly define the differences between graduate and undergraduate studies. They are basic and easy to see. The undergraduate is learning about university, himself and different fields of study. The social aspects can be as important as the classes in many cases. The graduate studies are highly focused and specific. The graduate student already knows what he wants to study and do, now he just needs to learn how to do it! In undergraduate school you are like in kindergarten, learning how to adjust and deciding what you need to know. In graduate studies, like in High School, you know what you want to do, you just have to learn how to do it!
Those are the differences between graduate and undergraduate study.