To understand how water moves in our world, attention must be directed to the hydrologic cycle. The hydrologic cycle is essentially a water continuum, representing the different paths through which water circulates and is transformed in the natural environment (Fig. 1). Being a cycle, it has no specific beginning or ending. Rather, liquid water from the Earth s surface, particularly the oceans, is evaporated into a gaseous form and enters the atmosphere as water vapor (clouds). The atmospheric moisture is eventually returned to the Earth s surface in the form of rain or snow.
Cell differentiation. In developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type. Different tissues have different kinds of cells.
Cell-count distribution featuring cellular differentiation for three types of cells (progenitor z {\displaystyle z} , osteoblast y {\displaystyle y} , and chondrocyte x {\displaystyle x} ) exposed to pro-osteoblast stimulus. In developmental biology, cellular differentiation is the process where a cell changes from one cell type to another. Most commonly the cell changes to a more specialized type. Differentiation occurs numerous times during the development of a multicellular organism as it changes from a simple zygote to a complex system of tissues and cell types.