functional groups as substituents in naming?

[Sophia Xu 3F]

When we are doing naming for functional groups, do we treat the functional groups as substituents? like in the course reader, PROP-AN-AL C3H6 is just propanal, not 1-propanal because we neglect the 1 like we do in substituent namings?
for the molecule right below it, which has a KEYTONE attached to second carbon, its name is written as 2-PENT-AN-TONE to indicate the 2nd carbon.
so my question is in naming, do we treat the functional groups as substituents?
Thanks!

[Sophia Xu 3F]

and do we just neglect the 1 in PROPANE because ALDEHYDE group has to be at the end of the chain?

[Chem_Mod]

the number 1 is omitted in propanal because an aldehyde group must be at the end of a chain and is therefore 1 by default (not needed to be specified)

In 2-pentanone, we need to specify where the ketone is. There are only two possibilities: 2-pentanone and 3-pentanone. Note that it cannot be 1 because that would be an aldehyde, and 4 would be the same as 2 but with a higher (bad) number