Movement of Substance Across the Plasma Membrane ~

THE PLASMA MEMBRANE !

• The plasma membrane is a semi-permeable lipid bilayer found in all cells that controls water and certain substances in and out of the cell .

FUNCTION OF THE PLASMA MEMBRANE !

• Protects the cell.
• Separates the intracellular components from the extracellular environment.
• Controls what enters and exist the cell.

NECESSITIES FOR THE MOVEMENT OF SUBSTANCES ACROSS THE PLASMA MEMBRANE !

• To transport nutrients into the cell.
• For gases exchange.
• To excrete metabolic waste.
• To maintain the pH value and ionic concentration of the cell.

SUBSTANCES IN AND OUT THROUGH THE MEMBRANE !

• SUBSTANCES LEAVING A CELL ~
• Secretion
• Nitrogenous waste
• Oxygen
• Carbon dioxide
• Excess water
• SUBSTANCES ENTERING A CELL ~
• Nutrients
• Ionic salts
• Oxygen
• Carbon dioxide
• Water

• PERMEABILITY OF THE PHOSPHOLIPIDS BILAYER !
• The permeability of the phospholipids bilayer is determined by :
• The size.
• The charge.
• The polarity.
• Of substances pass through it.

• SUBSTANCE CAN MOVE THROUGH :
• Non-polar molecule : fatty acid, vitamin (A.D.E.K) steroid.
• Oxygen, carbon dioxide, water.
• SUBSTANCE CAN'T MOVE THROUGH :
• Ions : Na+, K+, Ca2+, H+
• Polar molecule : Polysacharides, amino acid, glucose, nucleic acids.

• WHAT IS PASSIVE TRANSPORT ??
• Passive transport is the movement of substances across the cell membrane without the use of energy by the cell.
• During passive transport, substances move down their concentration gradient, hence no energy is required.
• Passive transport can happen through three different channels, namely :
• Lipid bilayer.
• pore protein.
• carrie protein.

• WHAT IS DIFFUSION ??
• Diffusion is the movement of particles from high density region to a low density region. No energy is needed and no membrane involves in diffusion.
• THE DYNAMIC EQUILIBRIUM !
• Diffusion will continue until the concentration in all region is the same. When this happen, we say it has reached the dynamic equilibrium.
• FACTORS AFFECTING THE RATE OF DIFFUSION ( Hom fast diffusion happen ?? ) 
• Temperature
• Higher temperature - Diffuse faster
• Surface area
• Large surface - Diffuse faster
• Concentration gradient
• Higher gradient - Diffuse faster
• Size of particles
• Smaller particles - Diffuse faster
• Diffusion medium
• Solid - Slowest
• Liquid - Faster
• Gas - Fastest

• PARTICLES THAT MOVE THROUGH THE PLASMA MEMBRANE THROUGH DIFFUSION !
• Substances soluble in fat : fatty acid, glycerol, some vitamins (A.D.E.K).
• Neutral particles : water, oxygen, carbon dioxide.

• EXAMPLE OF DIFFUSION !
• Between alveoli and blood capillaries in the lung during gases exchange.

• WHAT IS OSMOSIS ??
• Osmosis is the diffusion of a water through a semi-permeable membrane, from a solution of high solute concentration to a solution with low solute concentration.
• It is a physical process in which a solvent moves, without input of energy, across a semi-permeable membrane separating two solutions of different concentration.

• IMPORTANT POINTS !
• It is a diffusion of water (normally) through a semi-permeable membrane.
• It is from a dilute solution to a more concentration solution.

• WHAT IS FACILITATED DIFFUSION ??
• Facilitated diffusion is the passive transport of substances across the plasma membrane with the help of transport proteins such as the channel protein and the carrier protein.