Question

what is a group of parts that work together as a whole?

Answer 1

There are several words that could qualify as that. If you think about machines, they have that nature. On and on the list can go. If you look at the words you might be able to pick from, some will probably have nothing to do with a group. You could eliminate those.

Answer 2

A system

Answer 3

Yes, that is one good one.