Chp - 3 , Diffusion....

• Diffusion


  Movement of particles from high to low concentration, stops at equilibrium
• Diffusion

  1. Movement of molecules or ions from a region of high concentration to a region of lower concentration / down a concentration gradient

  2. Result of their random movement
• Factors affecting diffusion


  • Distance molecules have to travel
  • Concentration gradient
  • Surface area (larger surface area, faster diffusion)
  • Temperature
  • Particle size (smaller particle size, faster diffusion)
• Osmosis


  Diffusion of water molecules through a partially permeable membrane from a region of high water concentration (dilute solution) to a region of low water concentration (concentrated solution)
• High concentration of water (dilute solution)

  High water potential
• Low concentration of water (concentrated solution)

  Low water potential
• Osmosis in animal cells

  1. Concentrated solution outside the cell, water moves out of the cell, cell shrinks

  2. Dilute solution outside the cell, water moves into the cell, cell bursts
• Plant cells in pure water

  • Do not burst due to strong cell wall
  • Vacuole pushes from inside by turgor pressure, keeps the leaves firm/upright
  • After water enters, the cell becomes turgid
• Osmosis in plant cells

  1. Concentrated solution outside the cell, water potential is lower, cytoplasm and vacuole shrink, cell membrane pulls away from cell wall (plasmolysed cell)

  2. Cell becomes flaccid (soft and floppy due to water loss)
• Active transport


  Movement of molecules against their concentration gradient, from low to high, requires energy from cellular respiration
• Active transport


  Carrier protein changes shape with energy provided by respiration, pushes ions into the cell