Aji, welcome to the board. I don't really have anything to add to what my esteemed colleagues have provided you with; they have done a very good job. The one example I thought of was a well-known song from an old Broadway musical [Annie Get Your Gun ?] which starts, "I can do anything better than you" and which goes on between two people, "No, you can't!" "Yes, I can!". Although this is an American musical and although can't would be spoken with the short, flat vowel, that vowel sound comes out rather silly when being sung, so it's sung with the deeper English pronunciation, or something close to it.

This put a question in my mind which you will be able to answer for me: If the tones in Chinese determine the meaning of words, how do you distinguish the tones when you are singing? Is there a way to separate the musical tone from the verbal tone?