exchange Flashcards
Fick’s law
rate of diffusion = (SA x conc. gradient) /diffusion pathway
4 adaptations of specialised exchange surfaces to increase the rate of exchange
- short diffusion pathway
- large surface area
- good blood supply
- selectively permeable membrane
main adaptation of fish gills in regard to diffusion
countercurrent blood flow - concentration gradient is maintained all the way along the gill
adaptations of insects when more oxygen is required then provided by diffusion (2)
- abdominal pumping - spiracles close, muscles pull skeletal plates of abdominal sections together, pumping air into air sacks deeper into the tracheoles
- at rest water leaks across cell membranes of muscle cells, when are respiring anaerobically, produce lactate which lowers water potential of muscle cells so water moves from tracheoles to muscle cells drawing air in tracheoles closer to muscle cells, reducing diffusion distance for oxygen
ATP
product of respiration used directly by cells for energy
when red blood cell enters capillary…
- slows slightly as is squashed, allowing more time for diffusion (pressure reduce)
tidal breathing
air goes in and out through the same route
pulmonary ventilation
air into the lungs per minute
eq. pulmonary ventilation
PV = TV (vital capacity) x BR (breathing rate)
mass transport system
a means by which materials are moved from exchange surfaces to other locations within the organism where the materials are required by cells, involves mass flow
structure of main fish gas exchange surface
gill filaments stacked in piles, with gill lamellae at 90 degrees to increase SA
adaptations for gas exchange in leaves (5)
- diffusion takes place in gas phase which is more effective than in water
- large air spaces - numerous interconnecting air spaces in mesophyll so gas readily comes into contact with mesophyll cells
- large SA of mesophyll cells = rapid diffusion
- many small pores - stomata - no cell is far from stomata = short diffusion pathway
- stomata surrounded by guard cells so can be opened/closed when needed - controlling rate of gas exchange
insect adaptations to reduce water loss (4)
- small SA:V to minimise area over which water is lost
- waterproof covering over body - chitin exoskeleton covered by waxy cuticle
- spiracles can be closed to reduce water loss (only at rest as conflicts with need for O2)
- tracheae carry oxygenated air directly to tissues
xerophytes
adapted to live in areas without much water
adaptations of xerophytes (5)
- thick waxy cuticle - waterproof barrier
- rolling up leaves - traps air around stomata on lower epidermis (underside of leaf) and increases water potential of trapped air, reducing water potential gradient and reducing water loss
- hairy leaves - (esp. lower epidermis) trap moist air next to leaf surface, reducing water potential gradient, reducing water loss
- stomata in pits/grooves - trap air, reducing WPG
- reduced SA:V of leaves - reducing area over which water loss can occur = slower rate of diffusion
mass transport system
a means by which materials are moved from exchange surfaces to other locations within the organism where the materials are required by cells - involved mass flow
open circulatory system
blood pumped by tubular, sac-like heart through short vessels into large spaces in the body cavity - blood bathes cells before reentering the heart through holes
closed circulatory system
blood pumped by heart through a series of arteries and veins - oxygen transported around body by blood and diffuses through capillary walls into cells
open circulatory systems useful for
the hydraulic movements of the body or its components
closed circulatory systems useful for
large, active animals where oxygen cannot easily be transported to the interior of the body - also allow more control over distribution of blood flow by contracting/dilating blood vessels
double circulatory system
where blood is pumped to the lungs separately to the body - pumped to lungs then returns to heart to be pumped around body
‘heart is myogenic’ meaning
its contractions are initiated from within the muscle itself rather then nervous impulses from outside
where is initial stimulus for contraction from
Sinoatrial node (SAN) in wall of right atrium
‘describe how a heartbeat is initiated and coordinated’ [5]
- the SAN sends out an impulse of electrical excitement which spreads out across atria causing them to contract
- non-conductive tissue layer (atrioventricular septum) stops the impulse being transmitted to the ventricles immediately
- the wave enters the AVN which, after a short delay (allowing time for the atria to empty and the ventricles to fill), conveys a wave of electrical excitement between the ventricles
- the Bundle of His conducts wave through atrioventricular septum to the branching fibres of purkyne tissue
- the wave is released from tissue, causing quick contraction of the ventricles, from the bottom of the heart upwards
features of an artery (9) [incl. pressure values]
- thick muscular wall
- much elastic tissue
- small lumen relative to diameter
- capable of constriction
- non-permeable
- valves in aorta + pulmonary artery only
- high pressure (10-16kPa)
- blood moves in pulses
- flows quickly
features of a vein (9) [incl. pressure values]
- thin muscular walls
- little elastic tissue
- large lumen relative to diameter
- not capable of constriction
- not permeable
- valves through all veins
- low pressure (1 kPa)
- no pulse
- flows slowly
features of a capillary (6) [incl. pressure values]
- only endothelium walls
- links arteries and veins
- blood Changes from oxygenated to deoxygenated
- blood pressure reducing (4-1 kPA)
- slow flow
- permeable
contents of tissue fluid
- glucose
- amino acids
- fatty acids
- ions in solution
- oxygen
role of tissue fluid
a means by which materials are exchanged between blood and cells - the immediate environment of cells
formation of tissue fluid
- as blood pumped through arteries to capillaries, high pressure is created at the arterial end of capillaries
- high pressure causes tissue fluid to move out of blood plasma, out of capillaries, although opposed by 2 forces:
- hydrostatic pressure of tissue fluid outside capillaries
- lower water potential of the blood due to plasma proteins that cause water to move back into the blood within capillaries
however, combined effect of all forces creates overall pressure which pushes tissue fluid out of capillaries
ultrafiltration
type of filtration under pressure - pressure is only great enough to force small molecules out fo capillaries, leaving behind all cells/proteins in the blood as too large to cross membranes
2 ways tissue fluid moves back into blood
- directly via capillaries, as a result of wp gradient and osmosis
- lymphatic system
how does tissue fluid return to blood 1 - (directly)
- loss of tissue fluid from capillaries reduces hydrostatic pressure inside them
- by the time it has reached venous end of capillary network, hydrostatic pressure is lower then that of tissue fluid around it
∴ tissue fluid forced into capillaries by high hydrostatic pressure - ALSO - plasma has lost water but still contains proteins ∴ has a lower water potential then tissue fluid
∴ tissue fluid moves back by osmosis down WP gradient
how does tissue fluid return to blood 2 - (lymphatic system)
- remaining 5% of tissue fluid drains into lymphatic capillary
- carried by vessels which gradually get bigger (pumped by the contracts on skeletal muscles) + hydrostatic pressure of exiting lymph at other end
- drains back into bloodstream via 2 ducts close to heart
SAN
sino atrial node
AVN
atrio ventricular node
passage of blood through heart
vena cava - right atrium - right ventricle - pulmonary artery - [LUNGS] - pulmonary vein - left atrium - left ventricle - aorta - [BODY]
process (summarised) of control of heartbeat
SAN - atria - AVN - [DELAY] - nerves - bundle of His - nerve - purine tissue - ventricles
high affinity for oxygen
takes up easily but releases less easily
low affinity for oxygen
takes up less easily but releases more easily
explain shape of oxygen dissociation curve
- shape of molecule makes it different for first oxygen to bind to a site as they are closely united ∴ low oxygen partial pressure, little oxygen binds on ∴ gradient of curve = shallow
- binding of first molecule changed quaternary structure, causing shape to change, making easier for oxygen to bind ∴ requires smaller increase in partial pressure to get 2nd O2 to bind then 1st O2 ∴ gradient increases
- after binding of 3rd molecule, although theoretically should be easier due to changing of quaternary structure, ore difficult as probability of collisions reduced as most binding sites occupied ∴ gradient flattens again
the further left the oxygen dissociation curve…
the higher the oxygen affinity
the further right the oxygen dissociation curve…
the lower the oxygen affinity
effect of increasing CO2 conc on oxygen affinity
makes it lower as more CO2 increases acidity of blood, causing haemoglobin to change shape
higher pH = … affinity
higher affinity - oxygen more easily loaded
lower pH = … affinity
lower affinity - oxygen less easily loaded but more easily released ∴ oxygen more easily released at respiring tissues ∴ more active the tissue, the more oxygen unloaded
structure of xylem vessels
long, tube-like structures formed from dead cells (vessel elements ) joined end to end
transpiration stream
continuous column of water in the vessels due to cohesion-tension
(transpiration –> water loss from leaves, cohesion between water molecules due to polarity and H-bonds mean water is pulled upwards)
how is water transported up xylem
- water evaporated from mesophyll cells into air spaces, and out through stomata
- water potential In mesophyll is lowered so water enters from neighbouring cells (ultimately from xylem)
- more water molecules are drawn up as a result of cohesion-tension, creating a transpiration stream up the xylem
- mineral ions actively transported I -> lower WP -> water In by osmosis = high HS pressure
where is the phloem located on vascular bundle
on the outside
source of phloem-transported materials
leaves
sink of phloem-transported materials
tips of roots and shoots and roots where sugars converted to starch
how does transportation in the phloem occur
- solutes produces In leaf diffuse into companion cell and are then transported into the phloem by active transport
- creating a low water potential, ∴ water moves into phloem by osmosis from xylem, creating high hydrostatic pressure
- at the sink glucose is used in respiration/converted to starch ∴ solute diffuses out of phloem, creating a high water potential
∴ water moves back into xylem by osmosis, creating a low hydrostatic pressure - the solution ∴ moves down the phloem, down the hydrostatic pressure gradient, from source to sink
role of companion cells
carry out living functions for sieve tube elements - eg. provide energy for AT
translocation
movement of solutes in a plant from source to sink
how is conc. gradient at sink maintained?
enzymes change solutes to ensure conc is lower then at source
evidence supporting mass flow theory (4)
- if rig of bark cut (including phloem but not xylem) from woody stem, bulge forms above the ring - fluid in bulge has HIGHER conc of sugars hone fluid below ring ∴ downwards flow of sugars
- radioactive tracer used to track movement of organic substances - eg. CO2 containing radioactive 14C
- pressure investigated using aphids - mouthpieces left in so sap comes out - faster nearer leaves = pressure gradient
- metabolic inhibitor (stops ATP production) introduced, translocation stops - evidence active transport is involved.
why does the aortic pressure increase at start of relaxation period?
- importance?
- gradually pressure falls (not below 12KPa) because of elasticity of the aortic wall creating RECOIL ACTION
- especial for blood to be continually delivered to tissues
