Secondary Active Transport

Intracellular transport of ions is critical in ensuring neurons work properly (Ahmed, 2013). Primary active transport is involved in the generation of an action potential within a neurone. An action potential is caused by ions, in the extra and intracellular fluid (Na +, and Cl-) having their concentration temporarily changed (Berndt et al., 2011) Sodium ions are actively transported out of the axon, of the neuron, and potassium ions are actively transported in. This is performed by the sodium-potassium pump. This establishes a potential difference of charge between the inside and the outside of the axon (both molecules are positively charged but the movement of sodium ions is greater to that of potassium 3:2). The required resting potential

Endodermal cells surrounding the xylem actively transport salts into the lumen using a H(+)-ATPase carrier protein (Lee et al., 2004). This lowers the lumens water potential and water now moves in down this gradient by the process of osmosis. This creates a force that helps to move water up the plant which is known as root pressure (Toole, G. and Toole, S., 2008) [3]. However the inward movement of water, as stated above, is an example of secondary active transport as the water is moving down a gradient that was set up by the original active transport of the salt that moved up

The second (the driven substrates) moves against its electrochemical gradient. (MICHAEL G. WOLFERSBERGER, 1994). Symporters result in both substrates moving, in the same direction e.g. in the loop on Henle with salt ions and water moving in through the urinary concentrating mechanism (Mount, 2014). Antiporters though result in both substrates moving in opposite directions e.g. sodium and potassium ions moving out and in of the axon of a neuron