As I can recall if you take B.Sc in Psychology, you'll be learning a fair bit of Biology especially how the brain system works as it relates to psychological function.

What kind of Biology are you looking for - the entire human body, just the brain alone or plants too?

If you're looking for more Biology, you'd have to look for a double major or double degree.

Psychiatry would require a medical degree... then further specialisation in Psychiatry.

Under a medical degree you'll be focusing more on diagnosis, surgery and treatment. Less Biology after 1st year...