List and Tuple initialized from string object

How the following two are differ:

>>> s = 'string'
>>> tuple(s)
('s', 't', 'r', 'i', 'n', 'g')
>>> tuple([s])
('string',)
>>> tuple((s))
('s', 't', 'r', 'i', 'n', 'g')
>>> tuple((s,))
('string',)
>>>    

String is an iterable object thats why it split into multiple element inside the tuple ?