  We measure different contributions to entropy production in a living
functional epithelial tissue. We do this by extracting the functional dynamics
of development while at the same time quantifying fluctuations. Using the
translucent Drosophila melanogaster pupal epithelium as an ideal tissue for
high resolution live imaging [1], we measure the entropy associated with the
stochastic geometry of cells in the epithelium. This is done using a detailed
analysis of the dynamics of the shape and orientation of individual cells which
enables separation of local and global aspects of the tissue behaviour. We find
intriguingly that we can observe irreversible dynamics in the cell geometries
but without a change in the entropy associated with those degrees of freedom,
showing that there is a flow of energy into those degrees of freedom. Hence the
living system is controlling how the entropy is being produced and partitioned
into its different parts.
