The students are more relaxed and their responsibilities are not that complicated and heavy in a sense that there are fewer requirements and their due dates are not immediate
In college you have greater responsibility. You are an adult, and they expect you to act like one. The teachers expect you to except the consequences if you do not do the required work. In high school the teacher would probably call your parents, and let them know that you aren't doing what you are supposed to do.
The subjects a student will learn and discuss are much more specific since you chose a career path you will take in the future
They have more responsibilities to study in college because the curriculum is much more specific and complicated because detailed topics are being discussed regarding your chosen career path