The combination of the finger-scan and the search code are then looked up in a central database, to ensure that they tally, before the transaction is approved.
That transaction itself happens to be fairly heavyweight, because it makes an extensive query of the database, and that might take one second, whereas normal transactions take one hundredth of a second.
Every transaction changes the balance in your account and as the bank gets new accounts or closes existing ones, that database must be updated to reflect accurately such changes as they happen.