Cell transport

• Diffusion


  The spreading out of particles, resulting in a net movement from an area of higher concentration to an area of lower concentration. Particles move down the concentration gradient-from an area of high concentration to an area of low concentration.
• Diffusion


  • No energy movement of particles required
  • Passive process
• Diffusion


  • Nutrients in the small intestine diffuse into the blood in 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
• 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
• 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
• 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


  • Urea diffuses from cells into the blood for excretion by the kidneys
  • 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
• Diffusion, osmosis, and active transport are different types of cell transport
• Factors affecting rate of diffusion

  • Difference in concentration (steeper gradient = faster rate)
  • Temperature (higher temperature = faster rate)
• Adaptations for exchanging substances

  • Single-celled organisms have a large surface area-to-volume ratio
  • Multicellular organisms have a small surface area-to-volume ratio and need specialised organ systems and cells
  • Exchange surfaces have a large surface area, thin membrane, and good blood supply
• Adaptations for exchanging substances

  • Villi in the small intestine
  • Alveoli in the lungs
  • Fish gills
  • Root hair cells
• Key terms


  • active transport
  • gill filament
  • alveoli
  • passive process
  • capillaries
  • gradient
  • osmosis
  • root hair cell
  • concentration
  • partially permeable membrane
  • diffusion