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a. adaptations for increase in body size & metabolic rate
Fick’s law
Rate of diffusion ∝ Surface area X Concentration difference
Thickness of gas exchange surface
- large SA:V ratio – to meet organism’s needs
diffusion pathway: distance molecules travel to reach all parts of organism
- thin – short diffusion distance
- permeable – to allow respiratory gases through
- moist – to allow gases to dissolve
- maintain concentration gradient
small animals – respiratory surface = general body surface – don’t need gas exchange organs
b. Unicellular: Amoeba – aquatic
- cell membrane: thin + partially permeable
- large SA:V (short diffusion path across whole cell) – diffusion through cell membrane sufficient to meet needs
- concentration gradient with water – O2 used in respiration
- moist: aquatic habitat
c. Simple multicellular
- limit to cell size & point where diffusion path too long for diffusion to be efficient
- smaller cell SA:V – slows diffusion
- low metabolic rate (O2 requirement)
Flatworms – aquatic
- permeable surface
- flattened – large SA:V = shortens diffusion path
- concentration gradient with water – O2 used in respiration
- moist: aquatic habitat
Earthworms (Annelids) – terrestrial
- permeable surface
- cylindrical – smaller SA:V ratio = larger diffusion path
- concentration gradient: closed circulatory system (Hb): O 2 removed from surface
capillary network: close to body surface – shortens diffusion path
- moist: secretes mucus + moist environment (soil)
d. large animals – specialised respiratory surfaces (larger = more specialised)
small SA:V & high metabolic rate (energy use / O2 needs): diffusion across body surface insufficient to meet needs
ventilation: actively maintain steep concentration gradient on specialised respiratory surface
fish (aquatic) – gills: held apart by flowing water – large SA for diffusion & moist
- gill filaments stick together – reduce SA for diffusion
- gills dry out: need moisture for diffusion
mammals (terrestrial) – internal lungs: maintain moist surface & reduce water & heat loss
- warm-blooded = high metabolic rate to generate heat – optimum for enzymes / high reaction rate
amphibians frog: skin (moist & permeable) + capillary network + lungs when active
reptiles: internal lungs – more complex & larger SA than amphibians
birds: high metabolic rate (for flight) – efficient ventilation mechanism
, e. ventilation: movement of fresh air in & stale air out
- supply respiratory surfaces with fresh supply of oxygen + remove high CO 2 concentration air
- maintains concentration gradient of O2 & CO2
+ circulatory system moves gases away from surface & between respiring cells
f. ventilation in bony fish
- 4 gill arches on each side of pharynx (throat)
- have 2 stacks of gill filaments along them (held apart by flowing water – large SA)
- covered in gill lamellae = gas exchange surface – increase SA
o thin epithelium + permeable
o dense capillary network
good blood supply (Hb binds to O2) – maintains concentration gradient
- operculum: bony plate – protects gills
o coordinated opening/closing with mouth
o pressure changes between buccal/gill cavity – ensures 1 way flow of water
mouth opens – buccal cavity floor lowers = volume increases & pressure decreases
water forced into mouth – down pressure gradient
mouth closes – buccal floor rises = volume decreases & pressure increases
water forced across gills – down pressure gradient
gill cavity pressure increases: operculum forced open – water leaves down pressure gradient
countercurrent flow – efficient: blood & water flow in opposite direction over gills
- always water > blood O2 conc = concentration gradient (exchange) along entire length of lamellae
- equilibrium never reached: reaches higher % saturation of O 2 (80% of available O2)
- constant rate of diffusion
parallel flow – cartilaginous fish: water & blood flow in same direction over gills
equilibrium reached along lamellae – can only absorb 50% of O 2 in water = less efficient
cartilaginous fish: no operculum to pump – must keep swimming to ensure oxygenated water flow over gills
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