Diffusion & Diffusion & TransportTransport

1. A 1. A concentration concentration gradientgradient exists exists where there is a where there is a difference in the difference in the number of number of molecules from molecules from one area to one area to another. another.

High High ConcentrationConcentration

Low Low ConcentrationConcentration

ConcentratiConcentration gradienton gradient

Medium Medium ConcentratioConcentrationn

MEMBRANE DYNAMICSMEMBRANE DYNAMICS

2. Molecules tend 2. Molecules tend to move from an to move from an area of area of highhigh concentration to an concentration to an area of area of lowerlower concentration. This concentration. This movement is known movement is known as as diffusiondiffusion. .

High High ConcentrationConcentration

3. 3. NetNet diffusion diffusion will stop when will stop when each area has each area has the the samesame concentrationconcentration Low Low

ConcentrationConcentration

Same Same concentration concentration

throughoutthroughout

Concentration gradients can also be found across Concentration gradients can also be found across cell membranes. cell membranes.

High Concentration

Low Concentration

4. Small 4. Small molecules like molecules like HH22OO, , OO22 and and COCO22 can easily can easily diffuse across diffuse across cell membranes. cell membranes. 5. 5. NetNet diffusion diffusion will stop when the will stop when the concentration on concentration on each side of the each side of the membrane membrane reaches reaches equilibriumequilibrium. .

Equilibrium has been reached

6. Even though the 6. Even though the concentration concentration gradient is now gradient is now gone, molecules gone, molecules can still can still diffusediffuse back and forth at back and forth at the same the same raterate in in both directions.both directions.

7. Each molecule 7. Each molecule type will diffuse type will diffuse across its across its ownown concentration concentration gradient.gradient.8. 8. Net Net diffusion will diffusion will stopstop when each when each molecule type molecule type reaches reaches its own its own equilibriumequilibrium..

9. Some small substances like 9. Some small substances like ionsions cannot easily cannot easily diffuse through the diffuse through the hydrophobichydrophobic region of the region of the membrane.membrane.10. This is because ions like 10. This is because ions like sodiumsodium and and potassiumpotassium have an electrical charge.have an electrical charge.

11. These ions 11. These ions are are repelledrepelled by by the membrane’s the membrane’s hydrophobic hydrophobic region.region.

12. Other molecules like 12. Other molecules like sugarssugars and and proteinsproteins cannot cannot diffuse through the membrane because of their diffuse through the membrane because of their large large sizessizes..

These molecules These molecules cannot diffuse cannot diffuse across the across the membrane on membrane on their own.their own.13. Molecules like 13. Molecules like these need a these need a facilitatorfacilitator or helper or helper to get across the to get across the membrane.membrane.

14. Special 14. Special transmembranetransmembrane proteins with internal proteins with internal channels are the helpers that will channels are the helpers that will facilitate facilitate the the diffusiondiffusion of these substances.of these substances.

Each Each substance substance requires its requires its own special own special protein.protein.15. This type of 15. This type of transport is transport is called called facilitativefacilitative diffusiondiffusion. .

16. Sometimes substances must be moved 16. Sometimes substances must be moved againstagainst their concentration gradient.their concentration gradient.

17. Special 17. Special transport transport proteins act as pumps to proteins act as pumps to accomplish this.accomplish this.

19. This type of 19. This type of movement is movement is called called active active transporttransport..

18. Energy supplied 18. Energy supplied from a molecule from a molecule called called ATPATP changes changes the shape of the the shape of the transport protein.transport protein.

ATP

ADP

Transport protein

P

Here is a sped-up model of active Here is a sped-up model of active transport.transport.

What is the molecule that provides the What is the molecule that provides the energy needed to operate the pump?energy needed to operate the pump?

It isIt is ATP. ATP.

20. In review, there are three basic ways substances 20. In review, there are three basic ways substances can be transported across a membrane.can be transported across a membrane.

A. A. DiffusionDiffusion (Passive; no (Passive; no energy required)energy required)B. B. FacilitativeFacilitative diffusion (protein diffusion (protein assisted; no energy assisted; no energy required)required)C. C. ActiveActive transport (energy transport (energy required)required)

ATP

ADPP