Hi,

Since, you are a science student, let me explain it through example of science. Example, after 12th you want to do something in science no matter what you do, you will have to get a bachelors degree. I might choose BSc as my graduate course. I cannot in any case do MSc first and then BSc without having bachelors degree. I might do BSc after MSc only if i want to do BSc again in that field again or in some other field.