Diffusion

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Diffusion- tendency of molecules of any substance to spread out in the available space

• passive transport- requires no energy from the cell to make it happen (diffusion is a type of)

• concentration gradient- a substance will diffuse from where it is more concentrated to where it is less concentrated

Diffusion Notes

Reaching equilibrium:• Molecules move in order to reach equilibrium• Once equilibrium is reached, molecules continue to move a

little to maintain equal spacing

Diffusion

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Diffusion Animation

Oct 11­9:16 AM

Facilitated Diffusionfacilitated diffusion­ the passive movement of molecules down its concentration gradient via a transport protein

Transport proteins:• may have specific binding sites for the solute• can become saturated when they are translocating passengers as fast as they can

• can be inhibited by molecules that resemble the normal “substrate”

• Many simply provide corridors allowing a specific molecule or ion to cross the membrane

– channel proteins­ allow fast transport

Diffusion

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Facilitated Diffusion Animation

Oct 11­9:16 AM

Active Transport

active transport­ requires the cell to expend its own metabolic energy; move solutes against their concentration gradient

ATP supplies the energy for most active transport

Diffusion

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Fig. 8.16 Both diffusion and facilitated diffusion are forms of passive transport of molecules down their concentration gradient, while active transport requires an investment of energy to move molecules against their concentration gradient.

Oct 11­9:37 AM

Sodium­Potassium Pump

• The sodium­potassium pump uses the energy of one ATP to pump three Na+ ions out and two K+ ions in

• AGAINST THE CONCENTRATION GRADIENT

Sodium Potassium Pump Animation (Active Transport)

Diffusion

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Oct 11­9:37 AM

Why do materials move across membranes?

• Maintain Homeostasis• Cells and all living things work to maintain homeostasis

> maintain an internal equilibrium > Constant and stable environment> Balanced

• Cells continually make adjustments• One way cells maintain homeostasis is to regulate the

movement of materials into and out of the cell