Cell membrane transport

Page
2

The type of molecule or ion diffusing. Large molecules need more energy to get them to move so they tend to diffuse more slowly. Non-polar molecules diffuse more easily than polar molecules because they are soluble in the non polar phospholipid tails.

Slide 14

Molecules that diffuse through cell membranes

Oxygen – Non-polar so diffuses very quickly.

Carbon dioxide – Polar but very small so diffuses quickly.

Water – Polar but also very small so diffuses quickly.

Slide 15

Facilitated diffusion

Large polar molecules such as glucose and amino acids, cannot diffuse across the phospholipid bilayer. Also ions such as Na+ or Cl- cannot pass.

These molecules pass through protein channels instead. Diffusion through these channels is called FACILITATED DIFFUSION.

Movement of molecules is still PASSIVE just like ordinary diffusion, the only difference is, the molecules go through a protein channel instead of passing between the phospholipids.

Slide 16

Slide 17

Facilitated Diffusion through a membrane

Cell membrane

Inside cell

Outside cell

Protein channel

Slide 18

Facilitated Diffusion through a membrane

Cell membrane

Inside cell

Outside cell

Protein channel

diffusion

Slide 19

Facilitated Diffusion through a membrane

Cell membrane

Inside cell

Outside cell

Protein channel

diffusion

EQUILIBRIUM

Slide 20

Facilitated Diffusion

Molecules will randomly move through the opening like pore, by diffusion. This requires no energy, it is a PASSIVE process. Molecules move from an area of high concentration to an area of low conc.

Slide 21

Facilitated diffusion

Slide 22

Osmosis

‘The diffusion of water from an area of high concentration of water molecules (high water potential) to an area of low concentration of water (low water potential) across a partially permeable membrane.’

Slide 23

Osmosis

Cell membrane partially permeable.

Inside cell

Outside cell

VERY High conc. of water molecules. High water potential.