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high concentration to low energy, because they are going
concentration. from high to low concentration.
One special kind of passive
To understand how this works,
transport is osmosis, when water
imagine blowing up a balloon and
crosses into the cell.
then letting the air out. When you
do this, the air flows out quickly You probably can figure out the
and without any extra energy second way substances can get
because it is going from a place into a cell. Since the first way was
where there are a lot of air getting in without energy, the
molecules (inside the balloon) to a second way is getting in with
place where there are fewer air energy. Since “active” is the
molecules (outside the balloon.) In opposite of “passive,” this method
other words, it is going from an is called active transport. As you
area of high concentration to low might expect, active transport
concentration. happens when the substance wants
to go from an area of low
Look at the figure below if you’re
concentration to high
having trouble with this idea.
concentration. Think back to the
balloon with air shooting out of it.
If you want to get air to go into the
balloon, where the concentration is
high, that’s going to require some
energy. ATP, the molecule created
by the mitochondria in the cell,
provides the energy for active
transport. Just like with passive
transport, proteins are sometimes
The red dots are all in the top left corner. This is needed to help out with active
where the concentration is the biggest. The dots will transport.
move down and to the right, until they are spread
out evenly.
Sometimes substances undergo Photosynthesis
passive transport all by
In the last section, we talked about
themselves. They just slide right
active transport needing energy.
through the cell membrane. Other
When you hear the word energy,
times they need a protein to help
you might think about playing
them make it across the
sports or running in a race.
membrane. But they never need
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