How many signatures are there in one non-multisig transaction

How many signatures are there in one non-multisig transaction

I checked this How is a transaction's output signed?.

I need clarification for:

For each input there is one signature, so there are as many signatures as there are inputs?

Why is that so and not use just one master signature per transaction, is it because sender of transaction can use funds from more than one address he controls?

Is there also a master signature that signs entire transaction or just the per input signatures mentioned before?

http://ift.tt/2jmCP6w