Difference between an ATO and CTO

[dabz]

Hi,

Sorry if this is a silly question but I've got my last ATPL exam tomorrow, ATPL Law and I can't figure out the difference between an Air Transport Op and a Commercial Transport Op.

I'm doing it correspondence so unfortunately I can't ask anybody...

Says in the book:

Air Transport Op means an operation for the carriage of passengers or goods by air for hire or reward except:

A Commercial Transport Op; or
A list of items such as sightseeing flight, joyriding VFR, microlight, gliding etc
Commercial Transport Op means an operation for the carriage of passengers or goods by air for hire or reward where:

Each passenger is performing, or undergoing training to perform a task or duty on the operation; or
the passengers or goods are carried to or from a remote aerodrome; except
that same list of items that was in an ATO.
I thought passengers were just that, paying passengers and they aren't performing any roles to do with a CTO.
Also a CTO says it carries passengers and/or goods to or from remote aerodromes but doesn't an ATO do the same thing?