Biology, Eighth Edition (Raven)

Chapter 38: Transport in Plants

How the Sodium Potassium Pump Works

How can more molecules be transported into areas with high concentrations of the molecule? Cells often need to create concentration gradients across membranes. The concentration of a molecule is much higher on one side of the membrane than the other when a concentration gradient exists. In order to create or maintain a concentration gradient, individual molecules must be moved from an area of low concentration to an area of high concentration. This cannot occur through passive diffusion, in fact diffusion will cause the gradient to break down. Only active transport, which requires both specialized transport molecules and the expenditure of energy can drive molecules up a concentration gradient. The sodium potassium pump is an important and well understood example of active transport.

View the animation below, then complete the quiz to test your knowledge of the concept.


1.	The sodium-potassium pump functions to pump

		A)	sodium ions out of the cell and potassium ions into the cell.
		B)	sodium ions into the cell and potassium ions out of the cell.
		C)	sodium and potassium ions into the cell.
		D)	sodium and potassium ions out of the cell.
		E)	sodium and potassium ions in both directions across the cell membrane.

2.	What is the source of energy used to power the sodium-potassium pump?

		A)	breakdown of ATP
		B)	formation of ATP
		C)	transport of ATP by the pump
		D)	breakdown of GTP
		E)	transport of GTP by the pump

3.	During one cycle, the sodium-potassium pump binds and moves.

		A)	1 Na⁺ and 2 K⁺.
		B)	2 Na⁺ and 2 K⁺.
		C)	2 Na⁺ and 3 K⁺.
		D)	3 Na⁺ and 2 K⁺.
		E)	3 Na⁺ and 3 K⁺.

4.	The sodium-potassium pump is a trans-membrane protein.

		A)	True
		B)	False

5.	The binding and release of sodium or potassium ions are due to conformational changes in the protein.

		A)	True
		B)	False