Molecule Transport
Two main categories of molecule transport exist in cells, active transport and passive transport(shown below). For small molecules such as oxygen, ethanol, and carbon dioxide, the molecules could easily cross the membrane via passive transport, in the form of simple diffusion through a concentration gradient. However, the means that cells use to transfer small molecules are not sufficient for transporting macromolecules, which include proteins, polynucleotides, andpolysaccharides. To transport these macromolecules, cells rely on active transport. There are two basic means of active transport - by exocytosis and by endocytosis. Exocytosis involves sending macromolecules out of the cell, while the opposite
Exocytosis
Macromolecules that are released don't simply drift towards the cell's membrane and squeeze their way out. They are actually packaged in a vesicle that separates them out from the rest of the cell. he vesicle fuses with its specific membrane structure and its contents are released without the vesicle, which is incorporated back into the cell's membrane.
Proteins, for example, that are to be secreted from the cell are made on the rough endoplasmic reticulum (ER). They are then transported to the Golgi complex by ER induced vesicles. The Golgi complex sorts and packages the proteins into vesicles that separate themselves off the Golgi complex and eventually fuse with the cellular membrane.