Because some apps need it
Ok so. At the top next to the 3.5 mm Head phone jack you will see a little hole. That is the microphone.
Yes.
It is on the very top of the iPad. If you look on the left side, you'll see two holes, a large one and a smaller one. The smaller one is the microphone.
The Microphone on the iPad Works when Needed, There is no on and off button for it.