I think that psychological states are more important and essential than biological states.
Identity:
If you had a brain transplant, where is your identity located? Does your identity follow your brain into a new body? Or does your identity stay with your biology?
Sentience:
Which would you prefer - to psychologically feel pain, but have no biological injuries; or to psychologically feel no pain, but have some biological injuries? The psychological state is what we care about, not the biology. The only reason you would prefer the biology is because you are choosing to care about future pain over pain in the present. Hence, the value of psychology over biology is inescapable.
Epistemics:
Based on Descartes thought experiment in skepticism, the fact that psychology exists is more epistemically reliable than the fact that biology exists - there is more truth value in psychology than biology.