Complex sentence: When "Saccharomyces cerevisiae" is grown below the sugar threshold and undergoes a respiration metabolism, the fermentation pathway is still fully expressed, while the respiration pathway is only expressed relative to the sugar availability.
Split into simpler sentences: When "Saccharomyces cerevisiae" is grown below the sugar threshold and undergoes a respiration metabolism, the fermentation pathway is still fully expressed. However, the respiration pathway is only expressed relative to the sugar availability.