diffusion

• diffusion:

  • the movement of particles from a higher concentration to a lower concentration of particles through a partially permeable membrane
  • net movement
  • passive transport - no energy required
• examples of diffusion in the body:

  • oxygen diffuses in and carbon dioxide diffuses out of the body through the alveoli - gas exchange
  • urea moves from the liver cells into blood plasma to be transported into the kidney for excretion
• factors that affect the rate of diffusion:

  • concentration gradient
  • temperature
  • surface area of the membrane
• concentration gradient:

  • difference in concentration between two areas
  • the greater the concentration gradient, the faster the rate of diffusion
  • more particles are moving down the gradient than against
• temperature:

  • the greater the temperature, the faster the rate of diffusion
  • the movement of particles is greater at a higher temperature
• surface area of the membrane:

  • the greater the surface area, the faster the rate of diffusion
  • more space for particles to move through
• surface area to volume ratio:

  • if this is large, the organism is less likely to require specialized exchange surfaces and a transport system
  • rate of diffusion is sufficient
  • volume is usually written as 1
  • volume = length * width * height
  • single celled organisms can use diffusion to transport molecules into their body
• adaptation:

  • having a large surface area, a thin membrane, and an efficient blood supply
  • the greater the surface area, the more particles can move through - faster diffusion rate
  • in the lungs, alveoli are one cell thick and round - allows for faster gas exchange, also have rich blood supply
  • in the small intestine, villi are finger like and one celled - increases surface area, the digested food can be absorbed in the blood faster
  • the flattened shape of leaves increases the surface area