Potassium transport proteins, so called potassium-channels, represent essential elements in the control of stomatal aperture. The performance of these microvalves and the related influence on the gas exchange in plants is illustrated by 3D-animations. A major part of the video focusses on the patch-clamp technique, a method, developed to record the activity of a single ion-channel molecule in vivo and in real time. The set up for high-resolution current recordings is introduced, an experiment is carried out and analysed. Stomatal movement and for the first time the formation of guard cell protoplasts are monitored using time-lapse cinemicrography.