Cell behaviour, from unicellular organisms to complex tissues, results from the interaction between evolutionary processes that shape the cells' structures, and physical laws that govern their environment. One of the best examples of direct interaction between a cell and its physical environment is given by the flagellum, a hair-like organelle 10 micrometres to 20 micrometres long. This is seen clearly in cells known as eukaryotic cells, found in certain kinds of algae. The flow of these cells, a phenomenon called cytoplasmic streaming, is not fully understood yet can reveal important scientific information, particularly from flagella behaviour. 'The biophysics of cytoplasmic streaming in Chara corallina' (Cyclosis) project, fully funded by the EU, studies this flow of cytoplasm and its intricacies. Project partners wanted to locate the reasons for the elusive behaviour of these cells so as to formulate better ways to combat diseased cells in the long run. The most evident characteristic of flagella is their incessant beating motion which they use for movement (e.g. in sperm cells or mucus clearance). The resulting flows are also involved in the establishment of embryonic left-right asymmetry, and may have even played a role in the development of multicellularity. Cells also use these organelles to probe chemical and mechanical properties of the surrounding environment. This perceptive ability is crucial for human conditions such as kidney disease. Hydrodynamics are involved in the direct interactions among individual microorganisms, giving a microswimmer clues about the presence of possible prey or predators and coordinating among flagella. Generally, however, little knowledge exists in this field. Project partners studied flagellar dynamics and swimming in a kind of green algae called Volvocales. Such algae are easy to grow and manipulate in the laboratory, with a short life cycle (one to two days), and easy-to-observe single cells. Flagellar motion is sporadically interrupted by 'slips' when one of the two flagella moves faster than the other, a phenomenon which has significant implications. Researchers found that these slips are induced by noise, an important discovery regarding the coordination of eukaryotic flagella. This also validated the role that physics plays in regulating hydrodynamic interaction. Such observations as well as differences in the behaviour of these cells have helped map how they navigate and why they move in the way that they do. The information can help unlock mechanisms behind different diseases, bringing researchers closer to finding cures. The project will contribute towards the development of a new area of biophysics, focused on problems that are more specifically biological. This presents an exciting opportunity for the European scientific community to build new and more integrated collaboration between physicists and biologists.