In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: In addition , mitochondrial respiratory dysfunction characterized by decreased respiratory control ratio and ADP / O was observed in isoproterenol - treated rats .
### Output Text:
In addition , mitochondrial respiratory dysfunction characterized by decreased respiratory control ratio and <span class="chemical">ADP</span> / O was observed in <span class="chemical">isoproterenol</span> - treated rats . 