Surface area to volume ratio
Small organisms
● Have a very large SA compared to their volume so faster heat loss + this heat is
replaced by a high metabolic rate
● So faster rate of aerobic respiration
● respiration/ metabolism replaces/ releases heat
● This allows efficient gas exchange as there is a big surface for exchange of substances
but there is also a smaller distance from the outside of the organisms to the middle of it
Larger organisms
● The larger an organisms is, the smaller its SA compared to its volume so faster diffusion
● Have a higher metabolic rate, which demands efficient transport of waste out of cells +
reactants into cells
● If species has higher metabolic rate, it uses more O2
Adaptations to increase SA: VR
● Villi + microvilli- maximise absorption of digested food
● alveoli + bronchioles- gas exchange in mammals
● Spiracles + tracheoles - gas exchange in insects
● Gill filaments + lamellae- gas exchange in fish
● Thin leaves- gas exchange in plants
● Many capillaries- capillary network
Explain the higher metabolic rate of small organisms
● Have larger SA: VR
● So faster heat loss
● Increased respiration to RELEASE heat
, Structure of the human gas exchange system
Inspiration IRAX
● External intercostal muscles + diaphragm contract
● Internal intercostal muscles relax
● Air press. In lungs decreases
● Vol of thorax increases
● Air moves into lungs down pressure grad, as atmospheric press. Is higher than that of
the thorax
● (Causes volume increase and) pressure decrease
Expiration: EXDRELAX
● External intercostal muscles + diaphragm relax
● Internal intercostal muscles contract
● Air press. In lungs increases
● vol of thorax decreases
● Air moves out of lungs down press grad as the press. In thorax is higher than that of the
atmosphere
Pulmonary ventilation calculation
● Is the total vol of air that is moved into the lungs during 1 minute
Pulmonary ventilation (dm3min-1) = tidal vol (dm3) x ventilation rate (min-1)
Small organisms
● Have a very large SA compared to their volume so faster heat loss + this heat is
replaced by a high metabolic rate
● So faster rate of aerobic respiration
● respiration/ metabolism replaces/ releases heat
● This allows efficient gas exchange as there is a big surface for exchange of substances
but there is also a smaller distance from the outside of the organisms to the middle of it
Larger organisms
● The larger an organisms is, the smaller its SA compared to its volume so faster diffusion
● Have a higher metabolic rate, which demands efficient transport of waste out of cells +
reactants into cells
● If species has higher metabolic rate, it uses more O2
Adaptations to increase SA: VR
● Villi + microvilli- maximise absorption of digested food
● alveoli + bronchioles- gas exchange in mammals
● Spiracles + tracheoles - gas exchange in insects
● Gill filaments + lamellae- gas exchange in fish
● Thin leaves- gas exchange in plants
● Many capillaries- capillary network
Explain the higher metabolic rate of small organisms
● Have larger SA: VR
● So faster heat loss
● Increased respiration to RELEASE heat
, Structure of the human gas exchange system
Inspiration IRAX
● External intercostal muscles + diaphragm contract
● Internal intercostal muscles relax
● Air press. In lungs decreases
● Vol of thorax increases
● Air moves into lungs down pressure grad, as atmospheric press. Is higher than that of
the thorax
● (Causes volume increase and) pressure decrease
Expiration: EXDRELAX
● External intercostal muscles + diaphragm relax
● Internal intercostal muscles contract
● Air press. In lungs increases
● vol of thorax decreases
● Air moves out of lungs down press grad as the press. In thorax is higher than that of the
atmosphere
Pulmonary ventilation calculation
● Is the total vol of air that is moved into the lungs during 1 minute
Pulmonary ventilation (dm3min-1) = tidal vol (dm3) x ventilation rate (min-1)
