cell transport

• what is diffusion?

  net movement of particles from an area of HC to LC along a concentration gradient - it is a passive process
• name 3 factors that affect the rate of diffusion:

  -the difference in concentrations

  -the temperature

  -the surface area of the membrane
• where in the body can diffusion be used?

  -villi in the small intestine; for absorbing nutrients

  -alveoli in the lungs for exchange

  -fish gills!

  -root hair cells
• how are villi adapted for exchanging substances?

  -long and thin; increases SA

  -one-cell thick; short diffusion pathway

  -rich blood supply; maintains a steep concentration gradient
• how are the lungs adapted for efficient gas exchange?

  -alveoli; provide a large SA

  -moist membranes; increases rate of diffusion

  -one-cell thick membranes; short diffusion pathway

  -rich blood supply; maintains a steep concentration gradient
• how are fish gills adapted for efficient gas exchange?

  -large SA for gases to diffuse across

  -thin layer of cells; short diffusion pathway

  -rich blood supply; maintains a steep concentration gradient
• what is osmosis?


  diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane
• what is active transport?

  movement of particles against a concentration gradient - from a DS to a CS- using energy from respiration
• why is active transport needed in plant roots?

  concentration of mineral ions in the soil is lower than inside root hair cells - ions must move against the concentration gradient to enter the root hair cells
• what is the purpose of active transport in the small intestine?

  sugars are absorbed when the concentration of sugar in the small intestine is lower than in the concentration in the blood