18044
Reactive oxygen species ( ROS ) have been long regarded as by - products of a cascade of reactions stemming from cellular oxygen metabolism , which , if they accumulate to toxic levels , can have detrimental effects on cellular biomolecules .
 Chemical: oxygen; Chemical: oxygen
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: oxygen; Chemical: oxygen