Diffusion

• Particles are always moving

• Particles move from areas of high concentration to low concentration

• Particles move until equilibrium is reached

• Particles move passively– No energy (ATP)

required– PASSIVE TRANSPORT

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html

Proteins

Recall the structure of the cell membrane…

• Selectively permeable = semipermeable– Regulates what enters and exits the cell

• Lipid bilayer (two layers of lipids = fats)• “Mosaic Model”

– Contains many types of proteins, pumps, channels, and receptors

Inside of cell (cytoplasm)

Outside of cell

Proteinchannel Lipid bilayer

Carbohydratechains

Diffusion Across the Cell Membrane

Diffusion Across the Cell Membrane

• Cell membranes are selectively-permeable - they allow some materials to pass across, but not others

(also called semipermeable)• If the membrane is permeable to a substance,

movement of that substance (solute) will occur as shown in the diagram below:

Facilitated Diffusion

• Facilitated Diffusion– No energy required – PASSIVE TRANSPORT– Uses a protein channel in the membrane

• Molecules move from high to low concentration

HighConcentration

LowConcentration

CellMembrane

Glucosemolecules

Proteinchannel

Osmosis

• Diffusion of water through a selectively permeable membrane (Osmosis is a form of facilitated diffusion.)

• PASSIVE TRANSPORT

The Effects of Osmosis on CellsAs a result of osmosis, cells respond differently when the water concentration inside the cell is equal to, greater than, or less than the water concentration in the environment.

Isotonic HypertonicHypotonic

Molecule tobe carried

Moleculebeing carried

Energy

Active Transport

• Requires energy• Moves materials from

area of LOW to HIGH concentration (against a concentration difference)

Active Transport

Diffusion, Osmosis, Facilitated Diffusion, or Active Transport?

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Diffusion, Osmosis, Facilitated Diffusion, or Active Transport?

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