Gas Exchange in PlantsGas Exchange in Plants

Reactions that involve gassesReactions that involve gasses

PhotosynthesisPhotosynthesis Occurs in the chloroplastOccurs in the chloroplast Energy produced (glucose)Energy produced (glucose) Greater volumes of gasses exchanged in Greater volumes of gasses exchanged in

photosynthesisphotosynthesis Cellular respirationCellular respiration

Occurs in the mitochondriaOccurs in the mitochondria Energy produced (ATP)Energy produced (ATP)

Where does the diffusion of Where does the diffusion of gasses occur?gasses occur?

Between the environment and the plantBetween the environment and the plant Diffusion through the stomataDiffusion through the stomata

Within the plantWithin the plant Gasses move in and out of the the Gasses move in and out of the the

intercellular spaces (spongy tissue) intercellular spaces (spongy tissue) Passive transportPassive transport

StomataStomata Where diffusion of Where diffusion of

gasses occursgasses occurs OO22 net movement out net movement out COCO22 net movement in net movement in

Underside of leavesUnderside of leaves Guard cells control Guard cells control

whether they are open or whether they are open or not (to leave them open not (to leave them open would be inefficient.would be inefficient.

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Guard Cells (GC)Guard Cells (GC) Kidney bean shapedKidney bean shaped Take in potassium by active transport – Take in potassium by active transport –

stimulated by light on the leafstimulated by light on the leaf Increases the particles in the cell therefore Increases the particles in the cell therefore

water enters by osmosis and GC swell water enters by osmosis and GC swell opening the stomata (because outer wall is opening the stomata (because outer wall is thinner making it bulge out)thinner making it bulge out)

Allow minerals out of GC and thus HAllow minerals out of GC and thus H22O leaves O leaves

via osmosis and the stomata closesvia osmosis and the stomata closes

Close the gates the water is Close the gates the water is getting out!getting out! Why not leave the stomata open?Why not leave the stomata open?

For gasses to pass across the cell For gasses to pass across the cell membrane they must be dissolved in membrane they must be dissolved in water water

Thus a film of water must surround the Thus a film of water must surround the GC’s GC’s

Why not leave the stomata Why not leave the stomata open?open?

So plants are constantly losing waterSo plants are constantly losing water This loss of water is called TranspirationThis loss of water is called Transpiration Without closing GC the plants would Without closing GC the plants would

become very dehydratedbecome very dehydrated

Sensitivity of StomataSensitivity of Stomata Number and appearance depend on Number and appearance depend on

environment conditionsenvironment conditions Hot, dry climates with low humidity have fewer Hot, dry climates with low humidity have fewer

stomatastomata High humidity = more stomata High humidity = more stomata Low COLow CO2 2 levels = stomata openlevels = stomata open

Normal levels of CONormal levels of CO22 = stomata relaxed = stomata relaxed

Beyond the LeafBeyond the Leaf In the roots and stem gas In the roots and stem gas

exchange occurs in the exchange occurs in the outer layer of cellsouter layer of cells

Lenticels break though Lenticels break though the bark (on woody the bark (on woody plants) and allow air to plants) and allow air to diffuse thoughdiffuse though

Within the plant diffusion Within the plant diffusion is used in the spongy is used in the spongy tissuetissue

LenticelsLenticels

OverallOverall Gas exchange in plants is completed by Gas exchange in plants is completed by

diffusiondiffusion No specific organ involvedNo specific organ involved

REFRENCESREFRENCES

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