Active Transport
Jessica Harwood
Douglas Wilkin, Ph.D.
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AUTHORS
Jessica Harwood
Douglas Wilkin, Ph.D.
EDITOR
Douglas Wilkin, Ph.D.
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Printed: March 29, 2015
CONTRIBUTORS
Doris Kraus, Ph.D.
Niamh Gray-Wilson
Jean Brainard, Ph.D.
Sarah Johnson
Jane Willan
Corliss Karasov
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C HAPTER
Chapter 1. Active Transport
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Active Transport
• Define active transport.
• Describe the process of active transport.
• Summarize the role of the sodium-potassium pump.
What does it take to roll a stone uphill?
This round stone tends to roll downhill due to the force of gravity. It takes an input of energy to push it uphill. Due to
diffusion, molecules tend to move from an area of high concentration (large amount) to an area of low concentration
(small amount). So guess what it takes to move molecules the opposite way, from an area of low concentration to an
area of high concentration? Energy, of course!
Active Transport
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
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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.
FIGURE 1.1
The
sodium-potassium
pump
moves
sodium ions to the outside of the cell
and potassium ions to the inside of the
cell. ATP is required for the protein to
change shape.
ATP is converted into
ADP (adenosine diphosphate) during
active transport.
Summary
• During active transport, a protein pump uses energy, in the form of ATP, to move molecules from an area of
low concentration to an area of high concentration.
• An example of active transport is the sodium-potassium pump, which moves sodium ions to the outside of the
cell and potassium ions to the inside of the cell.
Explore More
Use the resource below to answer the questions that follow.
• Osmosis and Active Transport at http://www.youtube.com/watch?v=6tVc5gyOzO4 (8:40)
MEDIA
Click image to the left or use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/57363
1.
2.
3.
4.
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What is active transport?
Where does a cell obtain the energy for active transport?
How does the body prevent the loss of sugar in urine?
List three factors that affect the movement of materials across a membrane. Explain how these factors affect
the movement of matter.
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Chapter 1. Active Transport
Review
1. How is active transport different from passive transport?
2. What form of energy is usually used in active transport?
3. Give an example of active transport. Explain what occurs during this process.
References
1. Hana Zavadska, based on image by Mariana Ruiz Villarreal (LadyofHats) (http://commons.wikimedia.org/wiki/File:Schem
sodium-potassium_pump-en.svg). Diagram of the sodium-potassium pump . CC BY-NC 3.0
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