Laminate over Different Surfaces

I was hoping to lay some laminate down in our kitchen diner which used to have carpet in the dining section but laminate in the kitchen. After removing the old carpet and laminate I have found that the kitchen has a concrete floor but the dining room has wooden floor boards. I have left the underlay in place in the kitchen because without it there will be about a 1cm difference in height between the floors.

Do I need different underlay for each section or can I use one for both? Can I use...

Laminate over Different Surfaces