MOVEMENT OF SUBSTANCES DIFFUSION

Learning Outcomes After completing this chapter, you will able to : Define diffusion as the movement of molecules from a region of their higher concentration to a region of their lower concentration down a concentration gradient

Surface area : volume ratio Volume = _______ Surface area = ______ Volume : Surface area ratio = ___________ Volume = _______ Surface area = ______ Volume : Surface area ratio = ___________

Passive Transport Cell uses no energy Molecules move randomly Molecules spread out from an area of high concentration to an area of low concentration.

3 Types of Passive Transport 1.Diffusion 2.Facilitative Diffusion – diffusion with the help of transport proteins 3.Osmosis – diffusion of water

Diffusion Before After Region of high concentration

Diffusion of Liquids

Diffusion in Life

Diffusion of Bromine

Diffusion in Living Organisms 2nd Law of Thermodynamics governs biological systems – universe tends towards disorder (entropy)  Diffusion  movement from high  low concentration  Diffusion  movement from high  low concentration

Diffusion in Living Organisms PASSIVE Diffusion is a PASSIVE process which means no energy is used to make the molecules move, they have a natural KINETIC ENERGY

Structure of cell membrane Lipid Bilayer -2 layers of phospholipids a.Phosphate head is polar (water loving) b.Fatty acid tails non-polar (water fearing) c.Proteins embedded in membrane Cell Membrane Phospholipid Lipid Bilayer

Proteins Polar heads love water & dissolve. Non-polar tails hide from water. Carbohydrate cell markers Fluid Mosaic Model of the cell membrane

Outside of cell Inside of cell (cytoplasm) Lipid Bilayer Proteins Transport Protein Phospholipids Carbohydrate chains Structure of the Cell Membrane Go to Section:

Cell Membrane is Selectively Permeable

Diffusion Through Phospholipid Bilayer What molecules can get through directly? – fats & other lipids inside cell outside cell lipid salt aa H2OH2O sugar NH 3  What molecules can NOT get through directly?  polar molecules H2OH2O  ions  salts, ammonia  large molecules  starches, proteins

High Concentration Low Concentration Cell Membrane Glucose molecules Protein channel Passive Transport: Facilitated Diffusion Transport Protein Through a  Cellular Transport From a- High Low

Facilitated diffusion: diffusion of specific particles through transport proteins found in the membrane a.Transport Proteins are specific – they “select” only certain molecules to cross the membrane b.Transports larger or charged molecules Facilitated diffusion (Channel Protein) Diffusion (Lipid Bilayer) Passive Transport: Facilitated Diffusion Carrier Protein AB

Diffusion in Living Organisms Diffusion of digested food through the cell lining the small intestine and into the blood Diffusion of oxygen into a root hair cell

Summary Passive transport No energy needed Molecules move from area of high to low concentration Diffusion is a passive transport Diffusion in living organism Across cell membrane