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The cell membrane

The cell membrane. Cell Membrane. Regulates what enters and leaves the cell Provides protection Provides support Fluid mosaic model Phospholipid bilayer Carbohydrates Proteins. Click to watch video . Transport through cell membranes.

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The cell membrane

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  1. The cell membrane

  2. Cell Membrane • Regulates what enters and leaves the cell • Provides protection • Provides support • Fluid mosaic model • Phospholipidbilayer • Carbohydrates • Proteins

  3. Click to watch video

  4. Transport through cell membranes • The phospholipidbilayer is a good barrier around cells, especially to water soluble molecules. However, for the cell to survive some materials need to be able to enter and leave the cell. • There are 4 basic mechanisms: • DIFFUSION • OSMOSIS • FACILITATED DIFFUSION • ACTIVE TRANSPORT

  5. Diffusion of liquids

  6. DIFFUSION Diffusion is the net movement of molecules (or ions) from a region of their high concentration to a region of their lower concentration, without energy (passive).The molecules move down a concentration gradient.As a result of diffusion molecules reach an equilibrium where they are evenly spread out.This is when there is no net movement of molecules from either side.

  7. Diffusion through a membrane Cell membrane Outside cell Inside cell

  8. Diffusion through a membrane Cell membrane diffusion Outside cell Inside cell

  9. Diffusion through a membrane Cell membrane Outside cell Inside cell EQUILIBRIUM

  10. What determines the rate of diffusion?There 4 factors: • The steepness of the concentration gradient. The bigger the difference between the two sides of the membrane the quicker the rate of diffusion. • Temperature. Higher temperatures give molecules or ions more kinetic energy. Molecules move around faster, so diffusion is faster. • The surface area. The greater the surface area the faster the diffusion can take place. This is because the more molecules or ions can cross the membrane at any one moment. • The type of molecule or ion diffusing. Large molecules need more energy to get them to move so they tend to diffuse more slowly. Non-polar molecules diffuse more easily than polar molecules because they are soluble in the non polar phospholipid tails.

  11. Molecules that diffuse through cell membranes • Oxygen – Non-polar so diffuses very quickly. • Carbon dioxide – Polar but very small so diffuses quickly. • Water – Polar but also very small so diffuses quickly.

  12. Osmosis ‘The diffusion of water from an area of high concentration of water molecules (high water potential) to an area of low concentration of water (low water potential) across a partially permeable membrane.’

  13. Osmosis CONCENTRATED SOLUTION DILUTE SOLUTION Cell membrane partially permeable. Sugar molecule VERY Low concentration of water molecules. VERY High concentration of water molecules. Outside cell Inside cell

  14. Osmosis Cell membrane partially permeable. Low concentration of water molecules. OSMOSIS High concentration of water molecules. Outside cell Inside cell AS Biology, Cell membranes and Transport

  15. Osmosis Cell membrane partially permeable. OSMOSIS Outside cell Inside cell EQUILIBRIUM. Equal water concentration on each side. Equal water potential has been reached. There is no net movement of water

  16. Osmosis • Two solutions with the same solute concentration are isotonic • No movement of solute or water • Solution with a greater solute concentration is hypertonic • Water will move into the solution • Solution with a lesser solute concentration is hypotonic • Water leaves the solution

  17. Click for video

  18. Facilitated diffusion • Large polar molecules such as glucose and amino acids, cannot diffuse across the phospholipidbilayer. Also ions such as Na+or Cl-cannot pass. • These molecules pass through protein channels instead. Diffusion through these channels is called FACILITATED DIFFUSION. • Movement of molecules is still PASSIVE, does not require energy • Molecules move from an area of high concentration to an area of low concentration

  19. Active Transport • Movement across the membrane that requires energy • Can be from low concentration to high concentration

  20. Active Transport • Endocytosis • Process of taking materials into the cell by means of infoldings, or pockets, of the cell membrane • When large particles are taken into the cell this is called phagocytosis. Clilck for video

  21. Exocytosis • Membrane of a vesicle surrounds material and fuses with the cell membrane, forcing the content out of the cell. Click for video

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