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: Studies were also conducted in renal epithelial LLC - PK1 cells and in mitochondria isolated from kidneys of all the experimental groups .
### Output Text:
Studies were also conducted in renal epithelial LLC - PK1 cells and in mitochondria isolated from kidneys of all the experimental groups . 