Exchange surfaces

• what do cells take in

  • oxygen -> aerobic respiration by DIFFUSION
  • water -> by OSMOSIS
  • glucose -> respiration + mineral ions by DIFFUSION
• what do cells release

  • CO2 -> aerobic respiration by DIFFUSION
  • urea -> waste product from proteins by DIFFUSION
• what is urea

  waste product from proteins
• what does rate of diffusion depend on

  • surface area to volume ratio
  • larger the SA:V -> faster rate of diffusion-> faster rate of exchange
• how do you calculate the surface area to volume ratio

  surface area / volume
• how does gas exchange take place in single celled organisms

  • gases + dissolved substances diffuse into + out of cell across cell membrane
  • due to HIGH surface area to volume ratio
• in multi-cellular organisms what is the surface area: volume ratio like

  Low
• why is a low surface area: volume ratio a problem

  difficult to transport enough substances into body to supply the total volume if the outer surface alone was used
• what is needed if there is a low surface area: volume ratio

  exchange surfaces -> to transport substances INTO + OUT of body
• what does the human lungs provide an exchange surface for

  • absorbing oxygen -> needed for respiration -> into BLOOD from the AIR in the LUNGS
  • transferring CO2 -> produced by respiration-> from BLOOD into LUNGS
• how are lungs adapted for gas exchange

  contains millions of tiny air sacks = alveoli
• what are alveoli

  millions of tiny air sacks
• what does the bronchi, trachea and alveoli look like

  look carefully at where the bronchi is

  
• where has the blood arriving to the alveoli returned from

  from the rest of the body
• what does the blood returning from the rest of the body contain

  • lots of CO2
  • little oxygen
• what is created between the plentiful of CO2 and the little oxygen

  • a large concentration gradient between BLOOD
  • and AIR inside alveoli
• does oxygen dissolve IN or OUT of alveoli

  OUT
• where does oxygen dissolve into

  • out of alveoli
  • into blood
  • to be transported to heart
• does CO2 diffuse IN or OUT of blood

  OUT
• Where does CO2 diffuse into

  • out of blood
  • into alveoli
  • to be breathed out
• describe the gas exchange diagram 


  .

  
• how is the alveoli adapted to maximise gas exchange in lungs

  • very thin -> one cell thick -> means gases have a short diffusion pathway
  • good blood supply -> maintains concentration of gradient of O2 + CO2
  • moist lining for dissolving gases
  • large combined surface area -> allows large amount of gases to be changed with each breath
• list 3 factors which affect rate of diffusion

  • distance -> shorter the distance that substances have to diffuse = faster rate of diffusion
  • concentration difference -> greater the difference in concentration = faster rate of diffusion
  • surface area -> greater surface area = faster rate of diffusion
• what is Frick's law

  the relationship between rate of diffusion + factors that affect it
• how do you calculate Fricks law

  rate of diffusion is proportional to SURFACE AREA x CONC DIFFERENCE/ thickness of membrane
• if the rate of diffusion doubles what happens to the surface area or concentration difference

  it also doubles OR thickness of membrane HALVES