The students in 1st of ESO are studying the systematic classification of the living beings. As a representative of the fungi kingdom we have studies yeast and we have investigated which are the required conditions to activate yeast. We have tested if yeast is activated when placed in coke, and we observed that it does. We have compared its life activity with samples immersed in tap water, water with sugar and sparkling water. As a result we have concluded that the presence of sugar in water is the responsible of the activity of yeast. The measure of the life activity of yeast has been carried out by collecting in a balloon the carbon dioxide released by yeast's respiration.