You can find the number of terms on each of the ontologies by going to AmiGO:
- Under the 'Advanced Search' section in the middle of the page, use the drop-down menu to choose "Ontology". You don't need to type anything on the 'Quick search' box.
- This action will send you to the 'Information about Ontology search' page. There, open the 'Ontology source' filter menu on the left. You will see that as of October-27-2015 the number of terms on per ontology were:
- 28,912 Biological process
- 10,900 Molecular Function
- 4,016 Celular component
If you need a reference for this information, you can cite the use of AmiGO according to information found at http://geneontology.org/page/go-citation-policy#GO_Data. You can find additional general information about these and other topics on the GOC's 2015 publication in Oxford's NAR at http://nar.oxfordjournals.org/content/43/D1/D1049