What are some examples of passive transport?

What is active transport? And what are two examples of it?

• What are two examples of active transport?

• Answer:

  The movement of molecules by diffusion always proceeds spontaneously, down a gradient of free energy or chemical potential, until equilibrium is reached. The spontaneous "downhill" movement of molecules is called PASSIVE TRANSPORT. At equilibrium, no further movements of solute can occur without the application of a driving force. The movement of substances against or up a gradient of chemical potential is termed ACTIVE TRANSPORT. It is not spontaneous and it requires that work be done on the system by the application of cellular energy..... Plant Physiology, 2nd Ed. by Lincoln Taiz & Eduardo Zeiger. Example #1 -- Electrogenic Transport: There is a net movement of charge. The plasma membrane H+ - ATPase (proton pump) generates the gradient of electrochemical potential of H+ across the plasma membranes. Vacuolar H+ - ATPas electrogenically pumps protons into the lumen of the vacuole. H+ - pyrophosphatase (H+ - PPase) electrogenically pumps protons into the Golgi cisternae. Example #2 -- ABC Transporters. Members of the ABC (ATP-binding cassette) superfamily of proteins are found on both the plasma membrane and in internal membranes and are energized directly by ATP hydrolysis. An ABC transporter has been found to secrete anti-fungal terpenes across the plasma membrane of tobacco cells. More commonly, ABC transporters are found at the tonoplast, where they are sometimes referred to as glutathione conjugate pumps, or GS-X pumps, since they often transport molecules that have been covalently attached to glutathione. Glutathione (GS) is a tripeptide (Glu-Cys-Gly) that functions as an important cellular antioxidant molecule (see textbook p. 274 for molecular structure). The vacuolar GS-X pumps of plant cells function in herbicide detoxification, protection against oxidative damage, pigment accumulation, and the storage of antimicrobial compounds (see textbook Chapter 13).