T3 exchange Flashcards
what happens to the SA:V as size of an organism increases
SA:V decreases as vol increases much more rapidly than SA. (therefore small organisms have large SA:V)
adaptions of single-celled organisms to facilitate exchange
-large SA:V - allows exchange by simple diffusion through cell-surface membrane as the have large SA and small vol so diffusion distance to all organelles is short
-cell walls are permeable (if they have one)
what is ficks law
rate of diffusion is proportional to
SA x conc diff / thickness of membrane
- for fast diffusion cells must have:
1. large SA
2. steep conc grad
3. thin membrane/short diffusion pathway
why do fish have gills
-internal gas exchange surface
-small SA:V so cant just use simple diffusion through membrane
-waterproof, gas-tight outer covering on skin doesnt allow exchange
structure of gills
- gill filaments - project from gill arches, have lamellae on, stacked in pile and held apart by water (to increase SA) - means in absence of water, filaments stick together
2.gill arch - supports 2 stacks of filaments each, tissue around arch contains blood vessels
3.lamellae - located on filaments, stacked perpendicular to filament, single layer of flattened cells that contain network of capillaries to maintain internal conc grad.
mechanism of gas exchange - fish
- water taken in through mouth and forced over the gills and then out through flap on either side of fish’s head.
2.flow of water over lamellae and flow of blood within lamellae are in opposite directions, creating a COUNTER-CURRENT system. - this avoids reaching equilibrium, where no net movement of substances occurs and maintains conc grad as there is always more oxygen in water than in blood.
why do insects need tracheal system
-system delivers oxygen directly to organs and tissues
-rigid exoskeleton is impermeable to gases
features of tracheal system in insects
- spiracles - openings in the exoskeleton which allow air to enter insect, have valves which can close to prevent water loss from tracheoles
2.trachea - tubes within insect which lead to smaller tracheoles, have rings of strengthened material to prevent them closing as air pressure fluctuates
- tracheoles - narrow, dead-end tubes that run between cells and into muscle fibres (sites of gas exchange), moist on the inside to allow gases to dissolve and be absorbed
what happens during activity - insect
-During activity, when an insect is respiring anaerobically, water located in the tracheoles diffuses by OSMOSIS into muscles due to lower Water Potential in muscle cells as lactic acid builds up.
-This causes air to be drawn into the tracheoles. As well as this, the final diffusion medium is in a gas, rather than a liquid, and the diffusion distance is reduced, meaning diffusion happens faster.
ventilation mechanism - insects
-very active insects need a more rapid intake of oxygen, so they create a mass flow of air into the tracheal system by using the abdominal muscles to create a pumping movement to draw air in
what happens during inspiration (brief)
-(inhalation)
-air pressure of atmosphere is HIGHER than air pressure in lungs, forcing air into the lungs.
-aided by pressure decrease in lungs as they expand
what happens during expiration (brief)
-(exhalation)
-air pressure in atmosphere is LOWER than air pressure in lungs, forcing air out of lungs
-aided by pressure increase in lungs as volume decreases
process of inspiration
- Diaphragm and EXTERNAL intercostal muscles CONTRACT, internal intercostal muscles relax
2.rib cage pulled upwards and outwards, increasing the volume of the thorax
3.increased volume causes lung pressure to decrease BELOW atmospheric pressure
4.air is drawn into the lungs down the pressure gradient
process of expiration
1.Diaphragm and EXTERNAL intercostal muscles RELAX, INTERNAL intercostal muscles CONTRACT
2.rib cage moves down and inwards, decreasing the volume of the thorax
3.decreased volume causes lung pressure to rise ABOVE atmospheric pressure
4.air moves out of lungs, down the pressure gradient
features of alveoli
- thin WALLS (not membrane) - epithelial cells are squamous (flattened), walls are one cell thick - short diffusion distance
-large no of alveoli - 500 million - large SA
-capillary network surrounding alveoli - capillary walls are one cell thick - short diffusion distance, brings deoxygenated blood to the alveoli - maintains conc grad
-located inside the body - keeps them moist so gases can dissolve for efficient diffusion and protection from damage and infection
structure of haemoglobin
-globular protein
-quaternary structure - 4 tertiary polypeptide chains (2 alpha, 2 beta) and an iron ION (prosthetic haem group)
-each polypeptide is associated w a haem group
-each haem group can bind to one mol of oxygen, meaning 8 oxygen mols can be transported by each haemoglobin molecule
what is association
loading/binding of oxygen from haemoglobin
occurs in lungs
what is dissociation and where does it occur
unloading/unbinding of oxygen from haemoglobin
occurs in respiring tissues to diffuse into respiring cells
what is affinity
how easily haemoglobin takes up/binds with oxygen
haemoglobin evolved to change behaviour (affinity) in different conditions:
1. high affinity - associates w oxygen easily, hard to dissociate - in lungs
2.low affinity - dissociates w oxygen easily, hard to associate - in respiring tissues
how does affinity change
-changed by pH
-in areas of high CO2 conc (dissolved as carbonic acid), pH is lowered (more acidic), meaning the bonds in the tertiary structure of haemoglobin are broken, and the chains change shape. this means the oxygen they were associated w is released
needs for different haemoglobin properties
1.different life stages - foetal haemoglobin has higher affinity than adult haemoglobin due to the lowered partial pressure and lowered saturation
2.different oxygen levels - organisms in low oxygen envs require haemoglobin that readily associates w oxygen eg mountain goats
3. different activity levels - organisms w high metabolic rates require oxygen that readily dissociates to release oxygen into tissues eg. lion/sloth
features of lugworm haemoglobin/oxygen dissociation curve
-sometimes underwater, sometimes not, so needs to extract as much o2 from leftover water when tide is out as possible.
-oxygen dissociation curve shifted LEFT
-HIGHER affinity - can have full saturation at lower partial pressure
features of llama haemoglobin/oxygen dissociation curve
-lives at high altitudes where air is thin so partial pressure is lower
-oxygen dissociation curve shifted LEFT
-HIGHER affinity
features of small mammal haemoglobin/oxygen dissocation curve
-small = high SA:V = lose heat easily
-high metabolic demand so oxygen dissociation curve shifted RIGHT.
-have LOWER affinity - oxygen dissociates more easily so cells can respire.
what happens to affinity in high CO2 - Bohr shift
-curve shifted right
-LOWER affinity - pH is lowered (due to dissolved co2 as carbonic acid)
-changed structure of polypeptides in haemoglobin (as bonds are broken) so dissociation occurs
what happens to affinity in low CO2 - Bohr shift
- curve shifted LEFT
-HIGHER affinity - pH is increased so haemoglobin has a tight structure which means association occurs.
need for double circulatory system
-2 separate pumps prevents oxygenated and deoxygenated blood from mixing
-means oxygenated blood can be pumped at high pressure
-if just one pump, blood would be too low pressure (and too slow) by the time it got back to the heart again
