Sunlight allows green algae to do more than just carry out photosynthesis. Some unicellular algae actually use light to switch the adhesion of their flagella to surfaces on and off – a phenomenon first discovered by physicists at the Göttingen Max Planck Institute for Dynamics and Self-Organization. These findings are particularly relevant to the development of bioreactors in which algae serve as a renewable raw material for producing biofuels.