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Page history last edited by gerryc 13 years, 5 months ago

C5. Movement of substances across membranes may be passive or require the expenditure of energy.


Student Outcome: C5.1

Understand that the movement of substances by diffusion and osmosis is passive.


Membrane transport processes may be categorized on the basis of their energy requirement. Transport in which the net movement is from higher to lower concentration does not require metabolic energy. This is passive transport, which includes simple diffusion, osmosis, and facilitated diffusion. Transport that occurs against a concentration gradient through a membrane to the region of higher concentration is active transport. This process requires the expenditure of metabolic energy and involves special carrier proteins.


Source: science.csustan.edu


This is a video on passive transport.


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Whereas, this one is on osmosis.

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Here are some useful if simple animations illustrating what happens during osmosis.


Some very useful interactives from Concord.org on Osmosis and Diffusion of gases - whoops! Looks like you need Internet Explorer to see them working. Oh well, we'll forgive the Concord people.

Student Outcome: C5.2

Understand that the active transport of substances against the concentration gradient requires energy. This energy is supplied by ATP.


If uncharged solutes are small enough, they can move down their concentration gradients directly across the lipid bilayer itself by simple diffusion. Examples of such solutes are ethanol, carbon dioxide, and oxygen. Most solutes, however, can cross the membrane only if there is a membrane transport protein (a carrier protein or a channel protein) to transfer them. As indicated, passive transport, in the same direction as a concentration gradient, occurs spontaneously, whereas transport against a concentration gradient (active transport) requires an input of energy. Only carrier proteins can carry out active transport, but both carrier proteins and channel proteins can carry out passive transport.


This video summarises the three main ways substances can be passed through the cell membrane.

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Source: http://www.accessexcellence.org/RC/VL/GG/passActiveTrans.html


A video on active transport - although it is also a very good summary of the structure of the cell membrane.


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