Gas exchange

• 5 features of a good gas exchange system

  - large surface area to volume ratio to increase surface area for exchange

  - very thin to reduce diffusion distance so materials can cross rapidly

  - selectively permeable to allow selected materials to cross

  - movement of the environmental medium e.g air to maintain a diffusion gradient

  - movement of internal medium e.g. blood to maintain a diffusion gradient
• why do single celled organisms not need a specialised gas exchange system

  - have a lower demand for oxygen

  - less need to remove as much CO2

  - have a larger surface area to volume ratio

  - diffusion distance is short enough to use surface area

  - diffusion happens quickly over cell surface
• Why do multicellular organisms need exchange surfaces?

  - have a higher demand for O2

  - greater need to remove CO2

  - have a smaller surface area to volume ratio

  - diffusion distance too great to just use surface area

  -diffusion would take too long without exchange surface
• explain the gas exchange system in insects

  1. higher O2 concentration in environment

  2. O2 enters spiracles (hole in chitin exoskeleton)

  3. O2 moves through tracheal tube(lines with rings)

  4. O2 moves through trachioles and into muscle cells (use O2 for aerobic respiration to produce ATP for muscle contraction)

  5. Higher CO2 concentration in muscle cells

  6. CO2 moves through trachioles, through tracheal tube and out of spiracles to environment
• how does the concentration of gasses change when the spiracles open and close

  - when spiracles are open O2 concentration increases and CO2 concentration decreases

  - when spiracles are closed O2 concentration decreases and CO2 concentration increases
• How is a concentration gradient created in insects

  as O2 is used by respiring cells it creates a diffusion gradient, drawing in O2 from air
• how do insects enable this mass transport

  contraction of muscles as insects move squeezes the trachea enabling the movement of air
• why are the end of trachioles filled with water

  - as muscles respire they produce lacate, lowering the water potential of cells

  - causes water inside trachea to move into muscle cells by osmosis

  - the volume of water in the tracheoles decreases drawing air in

  - this measnthe final diffusion pathway is in a gas rather than a liquid so is more rapid
• explain gas exchange in a fish

  1. water containing O2 enters the fish through its mouth and passes out through its gills

  2. each gilll is covered in many filaments which are covered in many smaller lamallae

  3. gases are exchanges through the lamallae due to counter current flow
• explain counter current flow in fish


  water and blood flow in opposite directions

  - this maintains a concentration gradient so O2 concentration is always higher in water than blood

  - equilibrium is not reached so there is constant diffusion across the entire length of the gill

  
• What are adaptations of fish gills that maximise gas exchange


  - MANY filaments covered in MANY lamallae - very large surface area for diffusion

  - Only 2 cells thick - short diffusion path

  - lamallae have lots of blood capillaries - speeds up diffusion and maintains gradient
• How are leaves adapted for rapid gas exchange


  - many stomata so no cells is far from the stomata

  - numerous interconnecting air spaces throuought the mesophyll

  - large surface areas of mesophyll cells
• how do stomata/guard cells control gas exchange


  - guard cells open stomata to allow for exchange of gasses during day.

  - water enters making the cells turgid

  - this opens stomatal pore

  -guard cells loose water becoming placid if plant is dehydrated as this caused pore to close
• What is a xerophyte?


  A plant adapted to living in dry conditions
• how do xerophytes conserve water


  thick waxy cuticle - reduce evaporation

  sunken stomata - traps moist air reducing concentration gradient between plant and air

  reduced stomata - fewer places for water to escape

  hairs on epidermis - traps moise air

  curled leaves with the stomata inside - protect from wind
• what is the order for the transport of O2 in a human

  mouth

  trachea

  bronchi

  bronchioles

  alveoli
• What is inspiration?


  breathing in
• what happens during inspiration


  - external intercostal and diaphragm muscles contract

  - ribcage moves up and out, diaphragm flattens

  - volume of thoracic cavity increases

  - lung pressure decreases to below atmospheric pressure

  - air flows down trachea into lungs down a pressure gradient
• is inspiration an active process


  yes requires energy
• What is expiration?


  breathing out
• what happens during expiration


  - external intercostal and diaphragm muscles relax

  - ribcage moves downwards and inwards, diaphragm becomes a dome shape again

  - volume of thoracic cavity decreases

  - air pressure increases above atmospheric pressure

  - air forced down concentration gradient out of the lungs
• is expiration an active processs

  no - It doesn't require energy
• what happens during forces expiration (e.g. blowing out candles)


  - external intercostal muscles relax

  - internal intercostal muscles contract

  - ribcage is pulled further down and further in
• how do you describe the movement of the 2 intercostal muscles during forces expiration


  antagonistic
• how are the alveoli adapted for gas exchange


  - squamous epithelial cells -one cell thick, flattened - short diffusion path

  - capillary runs close to alveoli to maintain concentration gradient - transporting CO2 to from alveoli and O2 away from alveoli

  - capillaries ahem squamous epithelial cells- short diffusion path

  - alveoli contain elastic fibres so can stretch and recoil- stretch to prevent bursting and recoil to help expel stale air
• how do you calculate pulmonary ventilation rate


  ventilation rate * tidal volume
• what is pulmonary ventilation rate

  total volume of air moved into the lungs during 1 minute
• what are the units for pulmonary ventilation rate

  dm^3min^-1
• what is ventilation rate


  number of breaths per minute
• what is tidal volume

  amount of air inhaled and exhaled during a normal breathing cycle.