I recently heard a non-native speaker have difficulty with words beginning <bio>. One thing one can safely say about such words is that the beginning is never pronounced biːəʊ. The <i> always represents the diphthong aɪ.
In a few words the second part of the prefix bears the main stress of the word and the pronunciation is baɪˈɒ. Here are some examples:
biography biology bionic
Notice the pronunciation of biographical = ˌbaɪəˈɡræfɪkl and biological = ˌbaɪəˈlɒdʒɪkl.
In some other words it is the first syllable of the prefix which bears the main stress. Here are some examples of this:
biome = ˈbaɪəʊm
biopic = ˈbaɪəʊpɪk
biopsy = ˈbaɪɒpsi
biorhythm = ˈbaɪəʊrɪðm
bioscope = ˈbaɪəʊskəʊp or ˈbaɪəskəʊp
biosphere = ˈbaɪəʊsfɪə or ˈbaɪəsfɪə
In longer words the first syllable of the prefix tends to bear a secondary stress. Examples:
ˌbioˈchemistry ˌbiodiˈversity ˌbioengiˈneering ˌbiotechˈnology
In some words of this sort the prefix can be pronounced ˌbaɪə, but you won’t go wrong if you stick to ˌbaɪəʊ for all of them.