Though cells can transport some solutes across the plasma membrane by diffusion

Question

Though cells can transport some solutes across the plasma membrane by diffusion alone, many other substances must be transported across the plasma membrane against the existing concentration or electrochemical gradient. These transport processes require an investment of cellular energy, typically in the form of ATP hydrolysis, and are referred to as active transport.

Active transport processes move the cell away from chemical or electrical equilibrium. In contrast, passive diffusion moves the cell toward equilibrium. The expenditure of cellular energy to maintain disequilibrium is essential to life.

Before beginning this tutorial, watch the clip of the Membrane Transport animation on the sodium-potassium pump. Pay particular attention to how many sodium ions (yellow spheres) and potassium ions (red diamonds) are transported for each ATP (yellow starburst) that is hydrolyzed, and the direction that each ion is transported.

Part A - Active transport by the sodium-potassium pump

All cells contain ion pumps that use the energy of ATP hydrolysis to pump ions across the plasma membrane. These pumps create an electrochemical gradient across the plasma membrane that is used to power other processes at the plasma membrane, including some transport processes. In animal cells, the main ion pump is the sodium-potassium pump.





Complete the diagram below using the following steps.

Drag the correct white label to the white target, indicating how many ions move through the pump and in which directions.
Drag the pink labels to the pink targets, indicating the relative concentrations of Na+ and K+ inside and outside the cell.
Drag the blue labels to the blue targets, indicating the relative charges inside and outside the cell.
(HINT: The sodium/potassium pump pumps two positively charge ions in one direction and 3 positively charged ions in the other directions. The side that is receiving the 3 positively charged ions is going to have an excess of + charge!!!)

Explanation / Answer

a. 3 Na + ions going up 2 K + ions going down

b. Na + high K+ low [outside cell]

c. excess + charge [outside of cell]

d. Na + low K+ high [inside cell]

e. excess - charge [inside cell]

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