In contrast a more concentrated saline solution would cause water to flow out

In contrast a more concentrated saline solution would

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4.6 Transport of Material Within Membrane-Bound Compartments During endocytosis, molecules in the extracellular fluid enter the cell through the formation of vesicles, called endosomes, from the plasma membrane During exocytosis, molecules within cells are packaged into secretory vesicles, which then fuse with the plasma membrane and release their contents into the extracellular fluid Transport of Molecules into Cells by Endocytosis Three forms of endocytosis: phagocytosis, pinocytosis, and receptor-mediated endocytosis o In all cases, extracellular fluid and sometimes particulate matter are brought into the cell by the formation of an endosome In phagocytosis (which means “cell-eating”), a cell uses amoeboid-like movements of its plasma membrane to extend the membrane around particulate matter in the extracellular fluid o When the membrane completely surrounds the particle, the two sides of the plasma membrane pinch together to form a large endosome called a phagosome in the cytoplasm; the particle and some extracellular fluid are inside the vesicle o In this manner, the cell engulfs the particle
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o Once inside the cell, the membrane of the phagosome fuses with the membrane of a lysosome, forming a phagolysosome, which exposes the engulfed particle to the degradative enzymes of the lysosome o The enzymes break down the particle and usable components are recycled o Common in certain white blood cells, which are responsible for removing foreign particles and bacteria from our bodies In pinocytosis (which means “cell- drinking”), the plasma membrane develops an indentation, and its outer edges pinch together to form an endosome in the cytoplasm o Occurs continuously in most cells o A nonspecific process, and the contents of the resulting vesicle comprise extracellular fluid containing dissolved solutes Receptor-mediated endocytosis is similar to pinocytosis in that the plasma membrane develops an indentation to form the endosome o Is specific o Proteins in the plasma membrane function as receptors that recognize and bind specific particles in the extracellular fluid o
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