During active transport, molecules move from an area of low concentration to an area of high concentration. This is the opposite of diffusion, and these molecules are said to flow against their concentration gradient. Active transport is called "active" because this type of transport requires energy to move molecules. ATP is the most common source of energy for active transport. As molecules are moving against their concentration gradients, active transport cannot occur without assistance. A carrier protein is always required in this process. Like facilitated diffusion, a protein in the membrane carries the molecules across the membrane, except this protein moves the molecules from a low concentration to a high concentration. These proteins are often called "pumps" because they use energy to pump the molecules across the membrane. There are many cells in your body that use pumps to move molecules. For example, your nerve cells (neurons) would not send messages to your brain unless you had protein pumps moving molecules by active transport. The sodium-potassium pump ( Figure 1.1) is an example of an active transport pump. The sodium-potassium pump uses ATP to move three sodium (Na+ ) ions and two potassium (K+ ) ions to where they are already highly concentrated. Sodium ions move out of the cell, and potassium ions move into the cell. How do these ions then return to their original positions? As the ions now can flow down their concentration gradients, facilitated diffusion returns the ions to their original positions either inside or outside the cell.
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active transport requires atp.
--> a. true b. false
active transport can be considered the opposite of diffusion.
--> a. true b. false
which statement is true concerning the sodium-potassium pump?
--> a) the pump moves sodium ions out of the cell and potassium ions into the cell. b) the pump moves sodium ions into the cell and potassium ions out of the cell. c) the pump moves both sodium and potassium ions out of the cell. d) the pump moves both sodium and potassium ions into the cell.
which statement is true concerning active transport?
a) during active transport, molecules move from an area of high concentration to an area of low concentration. --> b) during active transport, molecules move from an area of low concentration to c) active transport is called "active" because it involves a protein pump. d) active transport is called "active" because it involves an active channel protein.
your nerve cells pump sodium ions from the extracellular space into the cell. how do the sodium ions get back out of the cell?
a) by active transport b) by simple diffusion --> c) by facilitated diffusion d) all of the above
complete the following sentence. as molecules are moving against their concentration gradients, active transport cannot occur without ____.
a) a channel protein --> b) a carrier protein c) the sodium-potassium pump d) facilitated diffusion
why are active transport proteins referred to as pumps?
a) because they release energy into the cell. b) because they move molecules across the membrane. --> c) because they use energy to pump the molecules against their concentration d) all of the above
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