cell transport

• Diffusion


  • The spreading out of particles from an area of higher concentration to an area of lower concentration. Particles move down the concentration gradient.
• Diffusion


  • No energy required - passive process
• Diffusion in humans


  • Nutrients in the small intestine diffuse into the capillaries through the villi
  • Oxygen diffuses from the air in the alveoli into the blood in the capillaries
  • Carbon dioxide diffuses from the blood in the capillaries into the air in the alveoli
  • Urea diffuses from cells into the blood for excretion in the kidney
• Diffusion in fish


  • Oxygen from water passing over the gills diffuses into the blood in the gill filaments
  • Carbon dioxide diffuses from the blood in the gill filaments into the water
• Diffusion in plants


  • Carbon dioxide used for photosynthesis diffuses into leaves through the stomata
  • Oxygen produced during photosynthesis diffuses out of the leaves through the stomata
• Osmosis


  The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane. Water moves from an area of lower solute concentration to an area of higher solute concentration.
• Osmosis


  • No energy required - passive process
• Osmosis in plants


  • Water moves by osmosis from a dilute solution in the soil to a concentrated solution in the root hair cell
• Active transport


  The movement of particles from a more dilute solution to a more concentrated solution using energy from respiration. Particles move against the concentration gradient - from an area of low concentration to an area of high concentration.
• Active transport in humans


  • Active transport allows sugar molecules to be absorbed from the small intestine when the sugar concentration is higher in the blood than in the small intestine
• Active transport in plants


  • Active transport is used to absorb mineral ions into the root hair cells from more dilute solutions in the soil
• Factors affecting rate of diffusion


  • Difference in concentration (steeper gradient = faster rate)
  • Temperature (higher temperature = faster rate)
  • Surface area of membrane (larger area = faster rate)
• Adaptations for efficient exchange


  • Single-celled organisms have a large surface area to volume ratio
  • Multicellular organisms have specialised organ systems and cells with large surface areas, thin membranes, and good blood supply
• Adaptations in villi


  • Large surface area due to folding
  • Thin wall only one cell thick
  • Good blood supply
• Adaptations in alveoli


  • Large surface area
  • Moist membranes
  • One-cell-thick membranes
  • Good blood supply
• Adaptations in fish gills

  • Large surface area
  • Thin layer of cells
  • Good blood supply
• Adaptations in root hair cells

  • Large surface area
  • Lots of mitochondria for active transport