Songs are made up of two things, melody and words. Words are made up of consonants and vowels. In singing, vowels trump consonants in terms of importance. So in that regard, vowels are one of the the most important elements of singing. Vowel shapes in the mouth make each sound different and unique. The cool thing is, we can change the shape of our mouths to make different sounds for each vowel. Each sound sound is unique. If every song was sung on one vowel, it would be boring boring boring.
What are the vowels most important to singers? We use I, E, A, O, and U as primary or mother vowels. Remember - vowels are all about the sounds. How a vowel sounds is more important than how a word is spelled. Spelling is secondary here. So in reality vowels are all about mouth SHAPES. Check out the chart below: