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: Taken together , these events undoubtedly establish GSPE ' s abundant bioavailability , and the power to defend multiple target organs from toxic assaults induced by structurally diverse and functionally different entities in vivo .
### Output Text:
Taken together , these events undoubtedly establish <span class="chemical">GSPE</span> ' s abundant bioavailability , and the power to defend multiple target organs from toxic assaults induced by structurally diverse and functionally different entities in vivo . 