Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:It is likely to be responsible for generating the proton gradient in these organelles detected with MitoLight and Rhodamine 123 staining (Zierdt et al. 1988; Nasirudeen and Tan 2004) and MitoTracker (Hamblin et al. 2008; Stechmann et al. 2008).
Category: