This is a Golgi apparatus or dictyosome. The elongate sacs of the Golgi are part of the endomembrane system in a cell. Inside these stacks of membranes, the materials arriving from other parts of the cell are sorted and prepared for packaging.
The proteins or other materials arriving from the endoplasmic reticulum may enter the Gogi through the forming-face of the stack. Here, tiny vesicles (observed at either end of the stacks of membranes) arrive, bringing the materials to be sorted and packaged.
Once inside the stacks, the materials are sorted. We know very little about how this is accomplished at present. However we do know that most proteins are tagged with sugars or lipids and that these added components serve as a kind of "destination label". Somehow processes in the Golgi accumulate materials with matching tags and pinch them off into a vesicle on the secreting-face of the Golgi. That is the packaging function.
Secretion vesicles, containing materials tagged for the same destination, depart from the secreting face of the Golgi and migrate to the destination.
In some cases, the destination is the cell membrane. Upon arrival, the vesicles merge with the cell membrane and the contents are dumped into the spaces between the microfibrils of cellulose in the cell wall. This process of exporting materials out of the cell is usually referred to as exocytosis or secretion. Examples of materials to be exported into the cell wall environment of plants cells include cell wall monomers and oligomers along with enzymes to assemble the cell wall polymers. Other examples include cell-wall degrading enzymes to allow for cell growth, and later, pectinase to degrade the middle-lamella during senescence, abscission, and fruit ripening.
If the cell membrane forms vesicles to bring fluids or particles from between the cell wall fibers into the cell, the process is called endocytosis. If the materials coming into the vesicles are dissolved in fluids, the endocytosis is usually called pinocytosis. Pinocytosis happens in plant cells when they are placed in a sucrose solution (as in sweetening your strawberry slices). If the incoming materials are particulates, the endocytosis is usually called phagocytosis. Phagocytosis is believed to be the pathway by which endosybiosis was initiated to give rise to mitochondria, chloroplasts, and even flagella. In these cases the particulates were whole prokaryotic cells.
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