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Summary Leaf gas exchange
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Year 1 Biology AQA A level notes. Achieved an A* in my final exam using these notes. They are based on the mark scheme requirements.
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Leaf gas exchange summary notes05 December 2022 11:33
- When photosynthesis is occurring most carbon
dioxide is obtained from external air, most
oxygen diffuses out of plant
- When photosynthesis is not occurring- ie in the
dark- oxygen diffuses into leaf as it is constantly
being used for respiration- carbon dioxide
produced in respiration diffuses out
Structure
- Large surface area- Diffusion takes place in gas
phase which makes it more rapid - palisade and
spongy mesophyll tissue are surrounded by air
spaces over which gases can exchange which
increases the surface area for gas exchange
- Short diffusion distance- each photosynthetic cell
is surrounded by air spaces, chloroplasts are
positioned next to cell wall, cross section of leaf is
thin- minimises diffusion distance between open
stomata and photosynthetic cell
- Steep concentration gradient- in day time the
rate of photosynthesis is high, CO2 is being used
to synthesise glucose- this ensures that the
palisade and spongy mesophyll tissue have a low
CO2 concentration relative to the outside air-
CO2 diffuses down the concentration gradient
through the open stomata
Leaves
- Stomata - short diffusion distance - most on the
underside of leaf. Have guard cells that surround
them which open and close the stomatal pore-
controls rate of gas exchange - balances
conflicting needs of gas exchange and control of
water loss- close stomata when water loss would
be excessive
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