difusion

• Substances may move into and out of cells by diffusion across cell membranes
• Diffusion is the spreading out of:

  • the particles of a gas
  • or the particles of any substance in solution
• Diffusion results in an overall movement of particles down a concentration gradient : from high to low concentration
• The rate of diffusion increases when:

  • difference in concentration increases , so the concentration gradient increase
  • temperature increases , so particles move quicker
  • the surface area of the membrane increases
  • the thickness of the membrane decreases
• Diffusion explains why you can smell cooking from the next room and why ink spreads through a glass of water without stirring
• Diffusion also happens across membranes and through the bloodstream.
• Molecules pass through the membrane in both directions (from both sides)

  
  

  the rate of movement from left to right is greater than the rate of movement from right to left.

  
  

  There is a net movement of particles from left to right until their concentration is the same on both side
• • Diffusion is an important process for living things - it is how substances move in and out of cells.
• If someone sprays deodorant from the other side of the room, how does the smell reach your nose?

  Through a process called diffusion. The deodorant particles bump into air particles and are spread throughout the room. We smell the deodorant particles that reach our noses.
• Why does diffusion happen faster in gases than in liquids?

  The particles in gases have more energy and are more widely spaced out than the particles in a liquid. This means that gas particles will bump into each other harder and more often. Which makes gas particles spread out more quickly than liquid particles can.
• Why doesn’t diffusion happen in solids?

  Diffusion doesn’t happen in solids because the particles in a solid cannot move around, instead they vibrate about a fixed position.
• Particles remain in random and continuous motion before during and after diffusion
• Describe 3 examples of movement of substances into or out of animal cells b diffusion

  during gas exchange - oxygen moves into cells by diffusion and carbon dioxide moves out by diffusions

  Urea is a waste product - it moves out of cells into the blood plasma by diffusion
• In diffusion the substances moved are:

  • carbon dioxide
  • oxygeon
  • water
  • food substances
  • waste products eg urea