<P> In secondary active transport , also known as coupled transport or cotransport , energy is used to transport molecules across a membrane ; however , in contrast to primary active transport , there is no direct coupling of ATP ; instead it relies upon the electrochemical potential difference created by pumping ions in / out of the cell . Permitting one ion or molecule to move down an electrochemical gradient , but possibly against the concentration gradient where it is more concentrated to that where it is less concentrated increases entropy and can serve as a source of energy for metabolism ( e.g. in ATP synthase ) . The energy derived from the pumping of protons across a cell membrane is frequently used as the energy source in secondary active transport . In humans , sodium ( Na ) is a commonly co-transported ion across the plasma membrane , whose electrochemical gradient is then used to power the active transport of a second ion or molecule against its gradient . In bacteria and small yeast cells , a commonly cotransported ion is hydrogen . Hydrogen pumps are also used to create an electrochemical gradient to carry out processes within cells such as in the electron transport chain , an important function of cellular respiration that happens in the mitochondrion of the cell . </P>
cotransport is an active process in which the energy is supplied by
the electrochemical potential difference created by pumping ions in / out of the cell