3.1

Phagocytosis

  • Bulk transport

  • Phagocytosis: Cellular eating; the ability of some cells (such as white blood cells) to engulf large particles (such as bacteria) and digest these particles by merging the food vacuole in which they are contained with a lysosome containing digestive enzymes. 

Endocytosis

  • Another method of bulk transport

  • Process in which the plasma membrane furrows inward instead of extending out with pseudopods

  • Pinocytosis

    • A form of endocytosis 

    • A nonspecific process performed by many cells

    • Plasma membrane invaginates to produce a deep, narrow furrow

    • The membrane at the top of this furrow then fuses, and a small vesicle containing the extracellular fluid is pinched off and enter the cell

    • Pinocytosis allows a cell to engulf large molecules such as proteins, as well as any other molecules that may be present in the extracellular fluid

  • Another type of endocytosis involves a smaller area of the plasma membrane, and it occurs only in response to specific molecules in the extracellular environment

    • The extracellular molecules must bind to very specific receptor proteins in the plasma membrane, so the process is known as receptor-mediated endocytosis

Receptor-mediated endocytosis

  • The interaction of specific molecules in the extracellular fluid with specific membrane receptor proteins causes the membrane to invaginate, fuse, and pinch off to form a vesicle 

  • Vesicles formed in this way contain extracellular fluid and molecules that could not have passed by other means into the cell

Exocytosis

  • Process by which cellular products are secreted into the extracellular environment

  • Proteins and other molecules produced within the cell that are destined for secretion are packaged within vesicles by the Golgi complex 

  • During exocytosis, these secretory vesicles fuse with the plasma membrane and release their contents into the extracellular environment

  • When the vesicle containing the secretory products of the cell fuses with the plasma membrane during exocytosis, the total surface area of the plasma membrane is increased