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.
