Diffusion,osmosis,active transport

• Diffusion


  Particles move from a region of higher concentration to lower concentration
• Diffusion


  1. Particles move in both directions

  2. Net movement from high to low

  3. Particles end up evenly spread but continue to move
• Concentration gradient


  Difference in the concentration of a chemical across a membrane
• Factors affecting rate of diffusion

  • Concentration gradient
  • Temperature
  • Surface area of cell membrane
• Concentration gradient


  Greater concentration difference, quicker rate
• Temperature


  Higher temp, more kinetic energy, faster rate
• Surface area of cell membrane

  Greater surface area, faster rate
• Rate of diffusion is proportional to surface area and concentration difference, and inversely proportional to thickness of membrane
• Osmosis


  Movement of water molecules from a solution with high to lower concentration of water molecules through a partially permeable membrane
• Water molecules


  Move down their concentration gradient
• Active transport


  Movement of substances against their concentration gradient, requires energy from respiration
• Diffusion stops when the concentration is equal in both areas
• Concentration


  Dissolved molecules
• Concentrated


  Solute concentration
• Cells absorb


  Water
• Cells absorb water from the body
• Capillary tubing


  Allows diffusion
• Percentage change in mass

  Calculated as (final mass - initial mass) / initial mass x 100
• The change in mass may be written as +/- to indicate gain or loss
• The solute in the solutions must be that is too large to diffuse across the cell membrane
• Blotting removes surface water to increase the accuracy and reliability of measurements
• Repeating the test at each concentration and calculating the mean helps to reduce the effect of random errors