Require cellular energy, usually as ATP Saturates when substance reaches high concentrations due to lack of available protein. Secondary Active Transport Uses proteins similar to those for facilitated diffusion. Couples the movement of several different molecules in each cycle. Saturates when substance reaches high concentrations due to lack of available protein. Cotransport moves 2 or more molecules in the same direction across the membrane.
Counter transport moves molecules in opposite directions.
The gradient for one molecule can cause the other to move against its own diffusion gradient. Copyright 1999, Joe Patlak, Department of Physiology, University of Vermont. For comments, problems or questions regarding this web contact Joe Patlak .