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Biomembranes I: Membrane Structure and Transport
Concept 1: Membrane Structure
   Practice (1 page)
   Review (1 page)
Concept 2: Osmosis: Movement of Water Across Membranes
   Practice (1 page)
   Review (4 pages)
Concept 3: Selective Permeability of Membranes
   Practice (1 page)
   Review (4 pages)
Concept 4: Passive and Active Transport
   Practice (2 pages)
   Review (2 pages)
Concept 5: Mechanisms of Active Transport
   Practice (1 page)
   Review (4 pages)
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.


To rerun these animations go to the review page.

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.