Short Answer: It all depends on what actually is encrypted. E. g. if your boot partition itself is encrypted then grub2 in this early stage uses your password only to access and start loading the kernel. All unlocking after this stage doesn’t use your password(s) but refers to keyfile(s) that was/were added at the time the system was set up. Think of it as automatic “chain-unlocking”.
You can check by running:
sudo cryptsetup luksDump /dev/sdXn
on a partition set up this way. The LUKS header will contain at least two keys (slot0 is usually your password, slot1 the keyfile).
The file /etc/crypttab contains the information regarding what partitions should be unlocked and which keyfiles to use. You could add a separate home and a backup or data partition here, which would then be unlocked one after the other during boot.
Refer to ArchWiki for further information.