The growing Drosophila egg chamber is a cluster of 15 nurse cells and 1 oocyte. During oogenesis, the volumes of these cells increase by almost three orders of magnitude. This experimental system provides a platform for answering many important questions in cell regulation. For instance, how do the sizes and the numbers of cell organelles adjust to cell size? We are trying to answer this question for mitochondria, which are thought to be active in the nurse cells and inactive in the oocyte.