Cell transport

• diffusion


  the movement of particles moving from a high concentration to a low concentration
• Is energy required for diffusion?

  No- passive process
• Osmosis


  the movement of water particles from a high concentration to a low concentration through a semi-permeable membrane
• Is energy required for osmosis?

  No- passive process
• Active transport

  the movement of particles from a low concentration to a high concentration
• Is energy required for active transport?

  Yes- energy released by respiration
• Example of 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
• example of diffusion in fish

  • 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
• example of 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
• example of osmosis in plants

  water moves by osmosis from a dilute solution in the soil to a concentrated solution in the root hair cell
• example of 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
• example of 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 that affect the rate of diffusion

  • difference of concentration
  • temperature
  • surface area of the membrane
• Villi

  • good blood supply
  • thin wall (one cell thick)
  • large surface area due to folding
  • network of capillaries
• Alveoli

  • network of capillaries
  • rate of diffusion is increased because the membrane of the alveoli have large SA, is moist, is only one cell thick
• fish gills

  • stacks of thin filaments
  • large SA to increase diffusion
  • network of capillaries
• Root hair cells

  • lots of mitochondria to take in mineral ions by active transport
  • large SA helps efficient absorption of water and mineral ions
• what does turgid mean?

  full of water
• what does plasmolysed mean?

  keeps it's same shape
• what is meant by hypotonic?

  dilute solution
• what is meant by hypertonic?

  concentrate solution