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Cell Structure
and Function
Biomembranes
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DNA Structure
and Replication
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Biomembranes I:
Membrane Structure and Transport
Concept 4: Passive and Active
Transport
Most biologically important
solutes require protein carriers to cross cell membranes, by a
process of either passive or active transport.
![](images/FacilitR2.gif) ![](images/spacer.gif) ![](images/ActiveR2.gif)
Active transport uses energy to move
a solute "uphill" against its gradient, whereas in facilitated
diffusion, a solute moves down its concentration gradient and no
energy input is required.
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