transport in and out of cells

• how do substances move in and out of cells, across the cell membrane?

  via diffusion
• diffusion is the movement of ….?

  particles from a high to a low concentration
• gas exchange

  • oxygen moves from the lungs to the bloodstream
  • at the same time, carbon dioxide moves from the bloodstream to the lungs
• UREA


  urea diffuses from the cells into the blood plasma for excretion by the kidney
• why do humans need exchange surfaces?

  • to get oxygen into cells
  • to get nutrients
• what are factors that affect the rate of diffusion?

  • concentration gradient (difference in concentration)
  • the temperature
  • the surface area of the membrane
• a single-celled organism has a large surface area : volume ratio, so…?

  it allows enough molecules to diffuse in and out of the cell to meet the demands of the organism
• how are organ systems and surfaces specialised for exchanging materials?

  • large surface area
  • thin surface - diffuse a short distance
  • rich blood supply - maintains concentration gradient
  • ventilation - speeds up gas exchange
• what is osmosis?

  diffusion of water from a concentrated to a dilute solution through a semi-permeable membrane.
• (RP!!!) osmosis

  1. cut cylinders of potato
  2. measure their mass
  3. place the potatoes into different cylinders with different concentrations of sugar solution
  4. after a few minutes, remove the potatoes
  5. measure their mass
• what is active transport?

  • movement of substances that go against a concentration gradient
  • from a low to high concentration
• what does active transport require?

  energy from respiration
• active transport allows what to be absorbed into PLANT ROOT HAIRS

  • mineral ions
• active transport allows what to be absorbed into the BLOOD?

  • sugar molecules from lower concentrations in the gut to the blood