Diffusion

• What substances do cells need to take in for respiration?


  Glucose and oxygen
• Why do cells need to get rid of waste products?


  To eliminate substances that are no longer needed in the body
• How do dissolved substances and gases move into and out of cells?

  Across the cell membrane
• What is one of the main ways substances move across the cell membrane?

  Diffusion
• What is diffusion?


  • The spreading out of particles of a gas or solute
  • Results in net movement from higher to lower concentration
  • Caused by random movement of particles
• What is the net movement of particles during diffusion?

  From an area of higher concentration to an area of lower concentration
• What causes the random movement of particles in diffusion?


  The motion of the particles causes them to bump into each other
• How does a room full of boys and girls illustrate diffusion?


  • Boys on one side, girls on the other
  • Random movement leads to mixing
  • Represents how particles spread out in diffusion
• What happens to the rate of diffusion when there is a big difference in concentration?


  Diffusion takes place quickly
• What is the effect of a small difference in concentration on diffusion?


  The net movement by diffusion will be quite slow
• What is the formula for net movement in diffusion?


  Net movement = particles moving in - particles moving out
• What is the concentration gradient?


  The difference in concentration between two areas
• How does temperature affect the rate of diffusion?


  An increase in temperature speeds up particle movement
• What substances move into and out of cells by diffusion?


  • Simple sugars (e.g., glucose)
  • Gases (e.g., oxygen and carbon dioxide)
  • Waste products (e.g., urea)
• How does oxygen enter red blood cells?


  By diffusion from the air in the lungs
• How does oxygen move from blood cells to body cells?


  By diffusion down a concentration gradient
• How does carbon dioxide move out of body cells?


  By diffusion into red blood cells and then into the air in the lungs
• What is gas exchange in the lungs?


  • Diffusion of oxygen into blood cells
  • Diffusion of carbon dioxide out of blood cells
  • Occurs down concentration gradients
• How can individual cells be adapted for diffusion?


  • Increased surface area of the cell membrane
  • Folding of the membrane or tissue
  • Greater area for diffusion increases the rate