Chapter 5 Active Transport You Must Know • The role of active transport, including the sodium potassium pump and cotransport, in cells. CONCEPT 5.4: Active Transport • Active transport moves substances against their concentration gradients. • Active transport requires energy, usually in the form of ATP. • Active transport allows cells to maintain concentration gradients that differ from their surroundings © 2014 Pearson Education, Inc. • Sodium-potassium pump transports 3 sodium ions out of the cell and two potassium ions into the cell. EXTRACELLULAR FLUID 1 © 2014 Pearson Education, Inc. CYTOPLASM [Na] high [K] low [Na] low [K] high 2 6 3 5 4 ADP How Ion Pumps Maintain Membrane Potential • Membrane potential is the voltage across a membrane. • Voltage is created by differences in the distribution of positive and negative ions across a membrane. © 2014 Pearson Education, Inc. • Two combined forces, collectively called the electrochemical gradient, drive the diffusion of ions across a membrane. 1. A chemical force (the ion’s concentration gradient). 2. An electrical force (the effect of the membrane potential on the ion’s movement). • An electrogenic pump is a transport protein that generates voltage across a membrane. • The sodium-potassium pump is the major electrogenic pump of animal cells. © 2014 Pearson Education, Inc. Figure 5.16 The main electrogenic pump of plants, fungi, and bacteria is a proton pump. Electrogenic pumps help store energy that can be used for cellular work. EXTRACELLULAR FLUID Proton pump CYTOPLASM © 2014 Pearson Education, Inc. Cotransport: Coupled Transport by a Membrane Protein Proton pump Sucrose-H cotransporter Diffusion of H Sucrose Sucrose © 2014 Pearson Education, Inc.