Bulk materials pass through membranes via endocytosis and exocytosis

[Bernard NebelKeymaster]

 

The following video shows an amoeba engulfing (eating) two parameciums. Note how the membrane of the amoeba surrounds the parameciums such that they end up as a vesicle inside the amoeba where they proceed to be digested.

The reverse of this process may also occur. For example, the digestive enzymes (proteins) of saliva are made within cells of the salivary glands. They are packaged in vesicles and secreted to the outside by the membrane of the vesicles fusing with the cell membrane. These processes, technically called endocytosis (brining into cells) and exocytosis (exiting from cells) are shown and explained further in the following video:

Have students note that for materials to move through membranes via diffusion, osmosis, or active transport they must be broken down to individual molecules or ions. Endo- and exocytosis enable the “bulk” transfer of materials across membranes. Note that endo- and exocytosis are active processes; like active transport, they require cellular energy (ATP).

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