Essential Knowledge 2.B.2

Growth and dynamic homeostasis are maintained by the constant movement of molecules across membranes.

Passive transport does not require the input of metabolic energy; the net movement of molecules is from high concentration to low concentration. Passive transport plays a primary role in the import of resources and the export of wastes. Membrane proteins play a role in facilitated diffusion of charged and polar molecules through a membrane. External environments can be hypotonic, hypertonic or isotonic to internal environments of cells. (examples - glucose transport, Na+/K+ transport)

Activity transport requires free energy to move molecules from regions of low concentration to regions of high concentration. Active transport is a process where free energy (often provided by ATP) is used by proteins embedded in the membrane to "move" molecules and/or ions across the membrane and to establish and maintain concentration gradients. Membrane proteins are necessary for active transport.

The processes of endocytosis and exocytosis move large molecules from the external environment to the internal environment and vice versa, respectively. In exocytosis, internal vesicles fuse with the plasma membrane to secrete large macromolecules out of the cell. In endocytosis, the cell takes in macromolecules and particulate matter by forming new vesicles derived from the plasma membrane.

Students should be able to:

Lo 2.12 Use representations and models to analyze situations or solve problems qualitatively and quantitatively to investigate whether dynamic homeostasis is maintained by the active movement of molecules across membranes.