Hi...UCI *just graduated* senior here
UCI gives priority to people who are in that major so you may have difficulty getting the required classes in. The only time I came across non-bio majors in my classes is in the larger "specialized" upper division classes like Human genetics and even then they were two public health majors. If you are planning on using the upper div classes to fulfill your pre-reqs, I'd think twice about it. Its definitely possible but these classes are all on a curve and all the people that are in them are those that have survived the weeding out from the lower divs. Therefore, its harder to get good grades. Upper div bio also includes the labs (which are taken as 4 unit courses) separately from the class they're related to. These labs have a prereq called Bio100LW. Since ALL bio majors take this lab-class hybrid, it is nearly impossible to get into it (and thus you wouldn't be able to take this class).
What you can do is come in, finish a psychology degree, graduate and then take the pre-reqs in a post bac year. If you have yet to apply, I'd consider applying for the public health major. Public health has two tracks: policy and science. I believe either one will make it easier for you to take bio classes since they are required under this major. It is very difficult to transfer into the bio major since there are so many of us already. If you have any questions, feel free to pm me.
point of all this, as a psychology major it will be difficult for you to get into the upper division science courses.