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: The progressive nature of mitochondrial injury suggests that mitochondria , not other subcellular organelles , are the major site of intracellular injury .
### Output Text:
The progressive nature of mitochondrial injury suggests that mitochondria , not other subcellular organelles , are the major site of intracellular injury . 