If all life is related why are the relationships not always obvious in terms of resemblances, or how much organisms resemble each other

All life has a common ancestor which can be traced through different lineages. Due to the fact that any new generation comes from two parents who do not share the same features. As the number of generations increases the resemblance to previous ancestors begins to minimize. For example I have brown eyes just like my mother, however, my great great grandmother had hazel eyes. 

Nitrate poisoning for the first onebaby blue syndrome

The higher you go up the less oxygen there is