Derive all the leaf nodes from a GO MF level. The supported organism are "Homo sapiens / Human",
"Rattus norvegicus / Rat", "Mus musculus / Mouse", "Danio rerio / Zebrafish", "Caenorhabditis elegans / Worm",
"Arabidopsis thaliana / Cress", "Saccharomyces cerevisiae / Yeast", "Schizosaccharomyces pombe / Fission yeast",
"Drosophila melanogaster / Fruit fly", "Escherichia coli / E.coli".