<p>hey guys, I am an incoming freshman, abhorrently in Bio. Sys. Eng. Major. I am looking to transfer into BioChem. Currently, I am signed up for 21A, but for BioSci student, theya re taking 17A. So, is there a big difference between 17A and 21A? I mean 21A may be a bit harder, but is it by alot? As well, after I take 21A, what if I was to switch to 17B, would the transition be hard?</p>