Diffusion, Osmosis and Active Transport

• Diffusion

  The net movement of particles from an area of higher concentration to an area of lower concentration down a concentration gradient
• Diffusion


  1. Molecules move about randomly

  2. Molecules spread out over time

  3. Molecules become evenly distributed
• Diffusion can happen in both gases and liquids
• Cell membranes


  • Partially permeable
  • Only small molecules can diffuse through
  • Larger molecules cannot fit through
• Diffusion is a passive process that does not require energy from the cell
• Factors affecting rate of diffusion


  • Concentration gradient
  • Temperature
  • Surface area
• Larger concentration gradient


  Higher rate of diffusion
• Higher temperature


  Higher rate of diffusion
• Larger surface area


  Higher rate of diffusion
• Osmosis


  The net movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration
• Water concentration

  The amount of water as compared to the other molecules like sugars or salts that are dissolved in that water
• Solutes are the dissolving molecules in water
• Higher solute concentration


  Lower water concentration
• Lower solute concentration


  Higher water concentration
• Osmosis in cells


  Water particles diffuse from the outside of the cell (higher water concentration) down the concentration gradient into the cell (lower water concentration)
• Active transport


  The movement of molecules across a cell membrane from a region of lower concentration to a region of higher concentration, requiring energy from cellular respiration
• Active transport


  • Occurs across a membrane
  • Requires special proteins in the membrane to transfer molecules
• Energy for active transport


  Comes from cellular respiration, the process that happens mainly in the mitochondria when they break down glucose to release energy
• Root hair cells


  • Have a large surface area for absorption
  • Have lots of mitochondria to provide energy for active transport
• Active transport in root hair cells

  1. Absorb water and mineral ions like magnesium and nitrates from the soil

  2. Minerals are at a higher concentration inside the cell than outside, so they use active transport to move them against the concentration gradient