gas exchange in plants and animals 3.3.2 Flashcards
5 features of a specialised gas exchange surface
- high surface area to volume ratio to increase rate of exchange
- very thin, small diffusion pathway so faster rate of diffusion
- selectively permeable to allow selected materials to cross
- movement of the environment medium (eg air) to maintain a diffusion gradient
- a transport system to ensure the movement of the internal medium (eg blood) to maintain diffusion gradient
ficks law
surface area x concentration difference
——————————————————-
length of diffusion path
is diffusion more rapid in air or water
air
how is a leaf adapted for efficient gas exchange
large SA to volume ratio
very short diffusion pathway
air spaces in the spongy mesophyll layer
how do guard cells open and close stomata
when water enters guard cells swell and become turgid
thin elastic wall stretches with turgor pressure
thicker inelastic cell wall (against opening) does not
what is a xerophyte
plants that are adapted to living in areas where their water losses due to transpiration may exceed their water uptake.
cuticle
forms a waterproof barrier
the thicker the cuticle the less water can escape
hairy leaves
traps still moist air next to leaf surface
reduces water potential gradient
less water lost by evaporation
rolling leaves
protects lower epidermis from outside helps trap air within the leaf
region becomes saturated with water
water potential gradient disappears
stomata in pits/grooves
traps moist air next to the leaf,reducing water potential gradient
reduced SA:vol ratio
thin needles
reduce SA
reduce water loss
(but need to have enough SA for sufficient photosynthesis)
what is the internal system of tubes where gas exchange takes place in insects called
trachea
what are the smaller dead wand tubes of the trachea called
tracheoles
what are the open ends of the trachea called
spiracles
how is the diffusion gradient in the insect tracheal system maintained
O2 used up so concentration towards tracheole falls
creates a diffusion gradient
how does CO2 produce a gradient
creates a diffusion gradient in the opposite direction to oxygen
why is diffusion in insects efficient
diffusion in air is more rapid than in water
how are the trachea supported and kept open
rings of chitin
how can the spiracles be opened and closed
valves
what are present at the spiracles to help reduce evaporation
tiny hairs
how do tiny hairs at spiracles help reduce evaporation
keep humidity around opening to ensure there is a lower concentration gradient of water vapour - less is lost from insect by evaporation.
what are the ends of the tracheoles filled with
water
how does the volume of water in the tracheoles change when the insect is at rest
more water when at rest
less when active
during periods of intense activity lactate is produced from anaerobic respiration.
lactate is soluble, how does this affect the water in the tracheoles?
decreases water potential of muscle cells.
water therefore moves into the cells from the tracheoles by osmosis.
this decreases the volume of water in the tracheoles.
what affect does water moving out of the tracheoles have on diffusion pathway
oxygen is drawn into the tubes
creates a faster diffusion pathway
increases rate of gas exchange
(however results in loss of water which is a downside)
what is the main disadvantage of the tracheal system
their size is limited
how else does the insect reduce water loss (other than spiracle hairs)
2 ways
1 small surface area to volume ratio
2 rigid outer skeleton of chitin covered by a waterproof cuticle
how do fish ventilate
water maintains gas concentration gradient
water enters through mouth
exits through opercular valves
inspiration of fish
mouth opens
operculum closed
muscles on floor of buccal cavity contract
floor lowers
volume increases
pressure decreases below pressure of surrounding water
water enters
expiration of fish
operculum opens
mouth closed
volume of opercular cavity decreases
pressure in opercular cavity increases above surrounding water pressure
water moves out of opercular cavity down pressure gradient
structure of gills
thin filaments held by gill bar
each filament has thin lamellae containing blood capillaries
(where gas exchange takes place)
function relating to structure of gills (3)
filaments and lamellae provide large surface area
thin lamellae provide short diffusion pathway
blood capillaries transport O2 and CO2 and maintain diffusion gradient
what does counter current exchange mean
blood with high O2 conc meets water with maximum amount of O2
blood with little O2 meets water that has had most of it’s O2 removed
what is the importance of counter current exchange
blood is always in contact with water that has a higher O2 conc
diffusion gradient is maintained along whole length of lamellae
blood becomes 80-90% oxygenated
what is the drawback of a parallel flow mechanism (as opposed to counter current exchange)
blood only gets 50% oxygenated
