Transport in cells

• Diffusion


  The movement of molecules from an area of higher concentration to an area of lower concentration
• Particles (molecules and ions) in a liquid and a gas move continuously
• Because of this movement, particles will spread themselves evenly throughout a liquid or a gas
• If there is a situation where particles of a substance are in a higher concentration, they will move from this region to where they are in a lower concentration
• Particles will move in both directions, but there will be a net movement from high to low concentration
• Particles will end up evenly spread throughout the liquid or gas, but will continue to move
• Examples of diffusion in biological systems


  • Substances moving into and out of living cells
  • In a leaf
  • In the lungs
  • Liver cells
• Diffusion

  1. Substances move

  2. From an area

  3. Of high to low concentration

  4. Down a concentration gradient
• Substances moved by diffusion

  • CO₂
  • O₂
  • H₂O
  • Food Substances
  • Waste e.g urea
• Diffusion requires no energy
• Osmosis

  1. Water moves

  2. From a high to low concentration

  3. Across a partially permeable membrane

  4. Down a concentration gradient
• Substances moved by osmosis

  • Water
• Osmosis requires no energy
• Active Transport

  1. Substances move

  2. Against a concentration gradient

  3. Mineral ions into plant roots

  4. Glucose from gut into intestinal cells

  5. From where it moves into the blood
• Active transport requires energy
• Transpiration is the loss of water vapour from leaves by evaporation
• Transportation stream is the constant movement of water throughout the plant
• Leaves lose water due to transpiration
• Water vapour is lost through the stomata during transpiration
• Water is gained by the plants through the roots and pulled up to the leaves through the xylem during transpiration stream