1.6

• Diffusion


  The spreading out of the particles of a gas, or of any substance in solution (a solute), resulting in the net movement (overall movement) of particles from an area of higher concentration to an area of lower concentration
• Diffusion


  Particles move randomly and bump into each other, causing them to spread out
• Particles move randomly, but the net movement is from a region of high concentration to a region of low concentration
• Diffusion


  • Takes place because of the random movement of the particles (molecules or ions)
  • The motion of the particles causes them to bump into each other, and this moves them all around
• Diffusion model


  • A room containing a group of boys on one side and a group of girls on the other, where everyone closes their eyes and moves around briskly but randomly, causing them to scatter until the room contains a mixture of boys and girls
• Difference in concentration between two areas

  The greater the difference, the faster the rate of diffusion
• Concentration gradient


  The difference in concentration between two areas
• Concentration gradient


  The bigger the difference, the steeper the concentration gradient and the faster the rate of diffusion
• Increase in temperature


  Increases the rate of diffusion
• Increase in temperature


  • Means the particles in a gas or a solution move around more quickly, causing diffusion to take place more rapidly
• Cells


  • Dissolved substances move into and out of cells by diffusion across the cell membrane
  • Cells may be adapted to make diffusion easier and more rapid by increasing the surface area of the cell membrane
• Adaptations to increase diffusion

  • Folding up the membrane of a cell, or the tissue lining an organ, to increase the area over which diffusion can take place
• The diffusion of oxygen and carbon dioxide in opposite directions in the lungs is known as gas exchange