Transcript Gas Exchange in Plants

Gas Exchange in Plants
Reactions that involve gasses
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Photosynthesis
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Occurs in the chloroplast
Energy produced (glucose)
Greater volumes of gasses exchanged in
photosynthesis
Cellular respiration
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Occurs in the mitochondria
Energy produced (ATP)
Where does the diffusion of
gasses occur?
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Between the environment and the plant
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Diffusion through the stomata
Within the plant
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Gasses move in and out of the the
intercellular spaces (spongy tissue)
Passive transport
Stomata
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Where diffusion of
gasses occurs
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O2 net movement out
CO2 net movement in
Underside of leaves
Guard cells control
whether they are open or
not (to leave them open
would be inefficient.
Link to other pictures
Guard Cells (GC)
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Kidney bean shaped
Take in potassium by active transport –
stimulated by light on the leaf
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Increases the particles in the cell therefore
water enters by osmosis and GC swell
opening the stomata (because outer wall is
thinner making it bulge out)
Allow minerals out of GC and thus H2O leaves
via osmosis and the stomata closes
Close the gates the water is
getting out!
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Why not leave the stomata open?
For gasses to pass across the cell
membrane they must be dissolved in
water
 Thus a film of water must surround the
GC’s
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Why not leave the stomata
open?
So plants are constantly losing water
 This loss of water is called Transpiration
 Without closing GC the plants would
become very dehydrated
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Sensitivity of Stomata
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Number and appearance depend on
environment conditions
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Hot, dry climates with low humidity have fewer
stomata
High humidity = more stomata
Low CO2 levels = stomata open
Normal levels of CO2 = stomata relaxed
Beyond the Leaf
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In the roots and stem gas
exchange occurs in the
outer layer of cells
Lenticels break though
the bark (on woody
plants) and allow air to
diffuse though
Within the plant diffusion
is used in the spongy
tissue
Lenticels
Overall
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Gas exchange in plants is completed by
diffusion
No specific organ involved