PASSIVE TRANSPORT

1. Passive transport is the movement of substances across the plasma membrane from a region of high concentration to a region of lower concentration, that is going down a concentration gradient until a dynamic equilibrium achieved.
2. Therefore, this process does not require energy.
3. Substances move across the plasma membrane down the concentration gradient through three different ways:
(a) lipid bilayer
(b) carrier protein
(c) pore protein
4. Substances move freely either through
(a) simple diffusion
(b) osmosis
(c) facilitated diffusion (with the help of carrier proteins or pore proteins)




A. Simple Diffusion (Resapan Ringkas)

1. Molecules diffuse across the plasma membrane down the concentration gradient through the phospholipid bilayer until dinamic equilibrium achieved.
2. Substances involved:
(i) small uncharged polar molecules : oxygen, carbon dioxide, water. Example: exchange of gases between the alveolus and blood capillaries.




Gases exchange between the alveolus and blood capillaries








The process of simple diffusion





A simulation of simple diffusion process (built by the blogger using the macromedia flash software)




B. Osmosis

1. Osmosis is the diffusion of water molecules through the plasma membrane or semi-permeable membrane.

2. The net movement of water molecules is from a region of low solute concentration (high water concentration/dilute solution) to a region of high solute concentration through a semi-permeable membrane.

3. Example: the absorption of water by root hairs of a plant where the soil has a higher water concentration than the cytoplasm in the root hairs.









The process of osmosis










A simulation of osmosis process (built by the blogger using macromedia flash software)




C. Facilitated Diffusion (Resapan Berbantu)

1. Refers to the movement of hydrophilic molecules or ions across the plasma membrane with the help of transport proteins:
(i) transported by binding at the binding sites of carrier proteins (examples: larger uncharged polar molecules like glucose and amino acids). Then carrier proteins change their shapes. After the process, the carrier proteins return back to their original shapes.
(ii) through the pores of pore proteins (examples: small charged molecules like mineral ions).

2. Examples : transportation of molecules which are not soluble in lipids such as glucose, amino acids and mineral ions through the villus at the ileum.









(i) Facilitated diffusion through a carrier protein












A simulation of facilitated diffusion process through a carrier protein (built by the blogger using the Macromedia Flash software)







(ii) Facilitated diffusion through a pore protein






A simulation of facilitated diffusion process through a pore protein (built by the blogger using the Macromedia Flash software)