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: Maleate induced cell damage and reactive oxygen species ( ROS ) production in LLC - PK1 cells in culture .
### Output Text:
<span class="chemical">Maleate</span> induced cell damage and reactive <span class="chemical">oxygen</span> species ( ROS ) production in LLC - PK1 cells in culture . 