And the number of English language learners has increased by 65 percent between 1993 and 2004 compared to barely a 7 percent increase in the total K12 population, according to a 2006 study by the National Clearinghouse for English Language Acquisition.
Exocytosis. Photo by: Alila. Exocytosis is the cellular process in which intracellular vesicles in the cytoplasm fuse with the plasma membrane and release or secrete their contents into the extracellular space. Exocytosis can be constitutive (occurring all the time) or regulated. Constitutive exocytosis is important in transporting proteins like receptors that function in the plasma membrane. Regulated exocytosis is triggered when a cell receives a signal from the outside.
When vesicles fuse with the cell membrane in the constitutive pathway, their contents become part of the membrane and it increases in size. This is only temporary because the opposite process, endocytosis, is acting simultaneously to remove parts of the membrane.his is known as the regulatory secretory pathway. In the constitutive pathway, vesicles fuse with the plasma membrane on arrival, but secretory vesicles of the regulatory pathway only do so when the cell receives a signal.