1.4 Membrane transport

A membrane is a barrier.

Almost all membranes are semi-permeable.

Why?

Particles are moved across a membrane in four ways:

1.Simple diffusion2.Facilitated diffusion3.Osmosis4.Active transport

1. Simple diffusion

Particles moving from high to low concentrations, particles moving down a concentration gradient.

Passive process. Particles move between phospholipids

Oxygen can move easily (non-polar molecule).

Small polar molecules can pass relatively easily (at a low rate) but larger polar molecules e.g. urea, pass much more slowly.

See fig. 6. pg. 36

2. Facilitated diffusion

Particles moving through specific channels in the membrane.

These channels are typically very narrow, the diameter of the protein channel determines what type of molecule is able to pass through.

Passive process.

High to low concentration, movement down a concentration gradient.

Cells are able to control which types of channels are synthesised, which in turn controls diffusion in/out of the cell.

http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.html

3. Osmosis

Movement of water, water moves freely. The net movement of water is known as osmosis.

Intermolecular forces (e.g. hydrogen bonds) between substances dissolved in water can restrict its movement.

If something has a high concentration of solutes, it will have a low concentration of water.

Passive process. High to low centration, down the concentration gradient.

http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

4. Active transport

Substances absorbed against the concentration gradient.

Low to high concentration.

Active process – REQUIRES energy (uses ATP).

Globular proteins inside the membrane (pump proteins)

Fig. 10, pg. 38

http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html

Read text book pages, find examples of passive/active transport

McGraw hill animation, endo/exocytosis? Passive/active transport

Design lab???

PASSIVE TRANSPORT

What does passive transport mean?

Examples?

Task

How would you design an experiment to test osmosis?

Facilitated diffusionCarrier proteins inside the membrane , carrier proteins combine with a substance/molecule and transport it across the membrane.

Does not require energy

Very specific

Write a short paragraph to explain the difference

between Diffusion (simple), Facilitated diffusion &

Osmosis

Active transportRequires energy

Moves molecules against the concentration gradient

Uses pumps

Read pg. 35/36. Summarise the process into a short paragraph

EndocytosisPart of the membrane

‘pinches’ off forming a vesicle to transport incoming

molecules within the cell.

EXOCYTOSISVesicle joining the membrane,

releasing contents into extracellular region