Germination can be divided into a number of distinct stages including imbibition, starch breakdown and energy mobilization, and cell differentiation and elongation. These stages involve very different biological mechanisms and are sensitive to different environmental stimuli. Normally, during imbibition, water and oxygen move slowly into the kernel through the tipcap region. Membranes rehydrate and hormones are activated. During starch breakdown and energy mobilization, hormones induce embryo and aleurone cells to release enzymes that break down starch and convert it to sugar. Energy contained in the sugar is moved into the embryo. Embryo cells use the sugars to fuel cellular process including cell division, elongation, and differentiation. As root cells elongate the radicle emerges from the kernel followed by the plumule. After the plumule emerges from the soil the seedling begins photosynthesis and the plant becomes independent of the food supply stored in the kernel.