Diffusion

• Substances may move into and out of cells across the cell membranes via diffusion.
• What is Diffusion?


  the spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration
• What are some of the substances transported in diffusion?


  oxygen and carbon dioxide in gas exchange, and of the waste product urea from cells into the blood plasma for excretion in the kidney
• The greater the difference in concentration, the faster the rate of diffusion
• What factors effect diffusion?

  the difference in concentrations (concentration gradient) • the temperature • the surface area of the membrane
• A single-celled organism has a relatively large surface area to volume ratio. This allows sufficient transport of molecules into and out of the cell to meet the needs of the organism
• Diffusion


  The spreading out of particles resulting in a net movement from an area of higher concentration to an area of lower concentration
• Molecules that move in and out of cells by diffusion


  • Oxygen
  • Carbon dioxide
  • Urea
• Cells need oxygen for respiration


  Oxygen moves into the cell by diffusion
• Respiration produces carbon dioxide


  Carbon dioxide moves out of the cell by diffusion
• Urea is a waste product produced inside cells


  Urea diffuses out of the cells into the blood plasma
• Factors affecting the rate of diffusion


  • Difference in concentrations (concentration gradient)
  • Temperature
  • Surface area of the membrane
• Greater concentration gradient


  Faster diffusion
• Higher temperature


  Greater rate of diffusion
• Larger surface area of the cell membrane

  Greater rate of diffusion
• In multicellular organisms, surfaces and organ systems are specialised for exchanging materials. This is to allow sufficient molecules to be transported into and out of cells for the organism’s needs. The effectiveness of an exchange surface is increased by: • having a large surface area • a membrane that is thin, to provide a short diffusion path • (in animals) having an efficient blood supply • (in animals, for gaseous exchange) being ventilated.
• Diffusion

  The net movement of particles from an area of higher concentration to an area of lower concentration
• 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
• Partially permeable membrane

  Only some molecules can diffuse through, like water, glucose, and amino acids. Larger molecules like proteins and starch 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