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: Cardiac disturbances at the cellular and mitochondrial level , mitochondrial electron transport chain complexes I - IV and apoptosis - inducing factor , and oxidative stress markers have been analyzed .
### Output Text:
Cardiac disturbances at the cellular and mitochondrial level , mitochondrial electron transport chain complexes I - IV and apoptosis - inducing factor , and oxidative stress markers have been analyzed . 