Movement across membranes 1- Diffusion

How to molecules move across phospholipid bilayer membranes?

Starter: Explain how a fish in a sealed packet cannot be smelt, but open it and the room quickly smells like fish.

Success Criteria

• What is meant by passive transport ( diffusion and facilitated diffusion including the role of membrane proteins), active transport, endocytosis and exocytosis.

• What is meant by passive transport ( diffusion and facilitated diffusion including the role of membrane proteins)

What do you know about diffusion?

?

What do you know about diffusion?

Kinetic energy

Goes both ways across

a membrane.

Equilibrium reached

Down a concentration

gradient

It is passive

?Molecules never

stop moving.

http://www.youtube.com/watch?v=2Th0PuORsWY

Diffusion

• The passive movement of molecules down a concentration gradient.

Equilibrium

• A point reached where the concentration of a molecule is the same on both sides of a ppm.

Simple Diffusion

There are different types of carrier proteins in the membrane:

ATP

Channel proteinGated-channel proteinCarrier protein(passive)

Carrier protein(active)

Fat-soluble diffuse down a concentration gradient. SOME water molecules can passively move – they are very small.

Extracellular space

Cytosoplasm (aqueous)

Polar molecules

Fat-soluble molecules diffuse down a concentration

gradient.

SOME water molecules can passively move – they are

very small.

Other small, non-charged molecules can diffuse

through e.g. O2 and CO2

Facilitated diffusion – channel proteins

Extracellular space

Cytosoplasm (aqueous)

Fat-soluble molecules and small molecules/ions diffuse through e.g. O2 and CO2

Polar moleculesLarge or charged molecules have to move through

proteins.

Some move through carrier proteins.

These carrier proteins are channels that allow 1 shape

through. Some are gated so can be

closed/opened.This is still diffusion and

passive.

E.g. Na+ gates in nerve cells

What about charged or large molecules?

Facilitated Diffusion – a gated channel protein

There are different types of carrier proteins in the membrane:

ATP

Channel proteinGated-channel proteinCarrier protein(passive)

Carrier protein(active)

Carrier proteins have a specific shape that bind to a specific molecule . E.g. glucose/Aa

The protein changed shape to allow the molecule through to the other side.

. O2 and CO2

Task – complete this table

Substance moved by Examples Simple diffusion

Sodium and calcium ions

Facilitated diffusion using carrier proteins.

What can affect the rate of diffusion?

• Use the text book page 23 to find out what affects the rate of diffusion and why.

Success criteria

• active transport, endocytosis and exocytosis.

Active transport

• Watch the animation on the next slide and explain how active transport works.

Active Transport

Inside of cell Outside of cell

ATP

P

ADP

Describe the role of active transport in across a cell membrane.

Protein carrierComplementaryCharged/largeATPEnergyFasterConcentration gradient.

Where is active transport used?

• Active transport includes:• Ca2+ pumps in muscles• Active reabsorption in nephrons• Absorption of the products of digestion• Sugar loading into phloem

One way

• The protein involved in active transport has a specific shape.

• This shape changes as the protein moves through it, using ATP.

• This change in shape means the protein cannot travel the other way through the protein.

Endocytosis vs Exocytosis

• The clue is in the name!

• Other words parts –

Phago – solid Pino – liquid.

What would you call the movement of a liquid into a cell?What would you call the movement of a solid out of a cell?

Movement of bulk materials using ATP.

• E.g.• Hormones• WBC