Within the TeefürPUK project we have today hosted a class from the Reithmanngymnasium in order to introduce the pupils into leaf gas exchange. Georg discussed with the pupils the basics of leaf CO2 and water vapour exchange and in particular strategies of plants involved in the regulation of stomatal conductance. Then pupils could get a hands-on experience with the Decagon porometers measuring stomatal conductance on a reference group of plants, drought-stressed plants and plants kept in the dark (simulating nighttime). Finally, results obtained by the pupils were discussed and related to the importance of stomatal conductance in regulating the water cycle and near-surface climate and the implications of changing environmental conditions.