How many signatures are there in one non-multisig transaction I checked this How is a transaction&#39;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?
1.: For typical P2PKH/P2PK you will always need to provide one signature. If all inputs spend outpoints of this form, then each one of them must provide one signature.

2.: They must sign a "special" transaction structure, see here: Redeeming a raw transaction step by step example required