Active Transport
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 a large amount to an area of a 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 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 below) 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.
The sodium-potassium pump moves sodium ions to the outside of the cell and
potassium ions to the inside of the cell, areas where these ions are already highly
concentrated. ATP is required for the protein to change shape. ATP is converted
into ADP (adenosine diphosphate) during active transport.
Summary
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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.
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.
Article Retrieved From: https://www.ck12.org/c/life-science/active-transport/lesson/Active-Transport-MSLS/?collectionCreatorID=3&conceptCollectionHandle=life-science-%3A%3A-activetransport&collectionHandle=life-science