Psychology is considered a "soft science". If your school's admission committee is composed of people with degrees in biology and chemistry, they will laugh if you send your psychology as a science LOR. Look at the website and if you have a specific question, just e-mail someone in the admissions office. It's better to contact them instead of base your decision off of something on here. 🙂 I am submitting a psy prof's LOR, but my school does not have a requirement of who the letters come from. They just require 3, one being a dentist.